Userland interfaces¶
The DRM core exports several interfaces to applications, generally intended to be used through corresponding libdrm wrapper functions. In addition, drivers export device-specific interfaces for use by userspace drivers & device-aware applications through ioctls and sysfs files.
External interfaces include: memory mapping, context management, DMA operations, AGP management, vblank control, fence management, memory management, and output management.
Cover generic ioctls and sysfs layout here. We only need high-level info, since man pages should cover the rest.
libdrm Device Lookup¶
BEWARE THE DRAGONS! MIND THE TRAPDOORS!
In an attempt to warn anyone else who’s trying to figure out what’s going on here, I’ll try to summarize the story. First things first, let’s clear up the names, because the kernel internals, libdrm and the ioctls are all named differently:
GET_UNIQUE ioctl, implemented by drm_getunique is wrapped up in libdrm through the drmGetBusid function.
The libdrm drmSetBusid function is backed by the SET_UNIQUE ioctl. All that code is nerved in the kernel with
drm_invalid_op()
.The internal set_busid kernel functions and driver callbacks are exclusively use by the SET_VERSION ioctl, because only drm 1.0 (which is nerved) allowed userspace to set the busid through the above ioctl.
Other ioctls and functions involved are named consistently.
For anyone wondering what’s the difference between drm 1.1 and 1.4: Correctly handling pci domains in the busid on ppc. Doing this correctly was only implemented in libdrm in 2010, hence can’t be nerved yet. No one knows what’s special with drm 1.2 and 1.3.
Now the actual horror story of how device lookup in drm works. At large, there’s 2 different ways, either by busid, or by device driver name.
Opening by busid is fairly simple:
First call SET_VERSION to make sure pci domains are handled properly. As a side-effect this fills out the unique name in the master structure.
Call GET_UNIQUE to read out the unique name from the master structure, which matches the busid thanks to step 1. If it doesn’t, proceed to try the next device node.
Opening by name is slightly different:
Directly call VERSION to get the version and to match against the driver name returned by that ioctl. Note that SET_VERSION is not called, which means the unique name for the master node just opening is _not_ filled out. This despite that with current drm device nodes are always bound to one device, and can’t be runtime assigned like with drm 1.0.
Match driver name. If it mismatches, proceed to the next device node.
Call GET_UNIQUE, and check whether the unique name has length zero (by checking that the first byte in the string is 0). If that’s not the case libdrm skips and proceeds to the next device node. Probably this is just copypasta from drm 1.0 times where a set unique name meant that the driver was in use already, but that’s just conjecture.
Long story short: To keep the open by name logic working, GET_UNIQUE must _not_ return a unique string when SET_VERSION hasn’t been called yet, otherwise libdrm breaks. Even when that unique string can’t ever change, and is totally irrelevant for actually opening the device because runtime assignable device instances were only support in drm 1.0, which is long dead. But the libdrm code in drmOpenByName somehow survived, hence this can’t be broken.
Primary Nodes, DRM Master and Authentication¶
struct drm_master
is used to track groups of clients with open
primary device nodes. For every struct drm_file
which has had at
least once successfully became the device master (either through the
SET_MASTER IOCTL, or implicitly through opening the primary device node when
no one else is the current master that time) there exists one drm_master
.
This is noted in drm_file.is_master
. All other clients have just a pointer
to the drm_master
they are associated with.
In addition only one drm_master
can be the current master for a drm_device
.
It can be switched through the DROP_MASTER and SET_MASTER IOCTL, or
implicitly through closing/opening the primary device node. See also
drm_is_current_master()
.
Clients can authenticate against the current master (if it matches their own) using the GETMAGIC and AUTHMAGIC IOCTLs. Together with exchanging masters, this allows controlled access to the device for an entire group of mutually trusted clients.
Parameters
struct drm_file *fpriv
DRM file private
Description
Checks whether fpriv is current master on its device. This decides whether a client is allowed to run DRM_MASTER IOCTLs.
Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting - the current master is assumed to own the non-shareable display hardware.
-
struct drm_master *drm_master_get(struct drm_master *master)¶
reference a master pointer
Parameters
struct drm_master *master
Description
Increments the reference count of master and returns a pointer to master.
-
struct drm_master *drm_file_get_master(struct drm_file *file_priv)¶
reference
drm_file.master
of file_priv
Parameters
struct drm_file *file_priv
DRM file private
Description
Increments the reference count of file_priv’s drm_file.master
and returns
the drm_file.master
. If file_priv has no drm_file.master
, returns NULL.
Master pointers returned from this function should be unreferenced using
drm_master_put()
.
-
void drm_master_put(struct drm_master **master)¶
unreference and clear a master pointer
Parameters
struct drm_master **master
pointer to a pointer of
struct drm_master
Description
This decrements the drm_master
behind master and sets it to NULL.
-
struct drm_master¶
drm master structure
Definition:
struct drm_master {
struct kref refcount;
struct drm_device *dev;
char *unique;
int unique_len;
struct idr magic_map;
void *driver_priv;
struct drm_master *lessor;
int lessee_id;
struct list_head lessee_list;
struct list_head lessees;
struct idr leases;
struct idr lessee_idr;
};
Members
refcount
Refcount for this master object.
dev
Link back to the DRM device
unique
Unique identifier: e.g. busid. Protected by
drm_device.master_mutex
.unique_len
Length of unique field. Protected by
drm_device.master_mutex
.magic_map
Map of used authentication tokens. Protected by
drm_device.master_mutex
.driver_priv
Pointer to driver-private information.
lessor
Lease grantor, only set if this
struct drm_master
represents a lessee holding a lease of objects from lessor. Full owners of the device have this set to NULL.The lessor does not change once it’s set in drm_lease_create(), and each lessee holds a reference to its lessor that it releases upon being destroyed in drm_lease_destroy().
See also the section on display resource leasing.
lessee_id
ID for lessees. Owners (i.e. lessor is NULL) always have ID 0. Protected by
drm_device.mode_config
’sdrm_mode_config.idr_mutex
.lessee_list
List entry of lessees of lessor, where they are linked to lessees. Not used for owners. Protected by
drm_device.mode_config
’sdrm_mode_config.idr_mutex
.lessees
List of drm_masters leasing from this one. Protected by
drm_device.mode_config
’sdrm_mode_config.idr_mutex
.This list is empty if no leases have been granted, or if all lessees have been destroyed. Since lessors are referenced by all their lessees, this master cannot be destroyed unless the list is empty.
leases
Objects leased to this drm_master. Protected by
drm_device.mode_config
’sdrm_mode_config.idr_mutex
.Objects are leased all together in drm_lease_create(), and are removed all together when the lease is revoked.
lessee_idr
All lessees under this owner (only used where lessor is NULL). Protected by
drm_device.mode_config
’sdrm_mode_config.idr_mutex
.
Description
Note that master structures are only relevant for the legacy/primary device nodes, hence there can only be one per device, not one per drm_minor.
DRM Display Resource Leasing¶
DRM leases provide information about whether a DRM master may control a DRM mode setting object. This enables the creation of multiple DRM masters that manage subsets of display resources.
The original DRM master of a device ‘owns’ the available drm resources. It may create additional DRM masters and ‘lease’ resources which it controls to the new DRM master. This gives the new DRM master control over the leased resources until the owner revokes the lease, or the new DRM master is closed. Some helpful terminology:
An ‘owner’ is a
struct drm_master
that is not leasing objects from anotherstruct drm_master
, and hence ‘owns’ the objects. The owner can be identified as thestruct drm_master
for whichdrm_master.lessor
is NULL.A ‘lessor’ is a
struct drm_master
which is leasing objects to one or more otherstruct drm_master
. Currently, lessees are not allowed to create sub-leases, hence the lessor is the same as the owner.A ‘lessee’ is a
struct drm_master
which is leasing objects from some otherstruct drm_master
. Each lessee only leases resources from a single lessor recorded indrm_master.lessor
, and holds the set of objects that it is leasing indrm_master.leases
.A ‘lease’ is a contract between the lessor and lessee that identifies which resources may be controlled by the lessee. All of the resources that are leased must be owned by or leased to the lessor, and lessors are not permitted to lease the same object to multiple lessees.
The set of objects any struct drm_master
‘controls’ is limited to the set
of objects it leases (for lessees) or all objects (for owners).
Objects not controlled by a struct drm_master
cannot be modified through
the various state manipulating ioctls, and any state reported back to user
space will be edited to make them appear idle and/or unusable. For
instance, connectors always report ‘disconnected’, while encoders
report no possible crtcs or clones.
Since each lessee may lease objects from a single lessor, display resource
leases form a tree of struct drm_master
. As lessees are currently not
allowed to create sub-leases, the tree depth is limited to 1. All of
these get activated simultaneously when the top level device owner changes
through the SETMASTER or DROPMASTER IOCTL, so drm_device.master
points to
the owner at the top of the lease tree (i.e. the struct drm_master
for which
drm_master.lessor
is NULL). The full list of lessees that are leasing
objects from the owner can be searched via the owner’s
drm_master.lessee_idr
.
Open-Source Userspace Requirements¶
The DRM subsystem has stricter requirements than most other kernel subsystems on what the userspace side for new uAPI needs to look like. This section here explains what exactly those requirements are, and why they exist.
The short summary is that any addition of DRM uAPI requires corresponding open-sourced userspace patches, and those patches must be reviewed and ready for merging into a suitable and canonical upstream project.
GFX devices (both display and render/GPU side) are really complex bits of hardware, with userspace and kernel by necessity having to work together really closely. The interfaces, for rendering and modesetting, must be extremely wide and flexible, and therefore it is almost always impossible to precisely define them for every possible corner case. This in turn makes it really practically infeasible to differentiate between behaviour that’s required by userspace, and which must not be changed to avoid regressions, and behaviour which is only an accidental artifact of the current implementation.
Without access to the full source code of all userspace users that means it becomes impossible to change the implementation details, since userspace could depend upon the accidental behaviour of the current implementation in minute details. And debugging such regressions without access to source code is pretty much impossible. As a consequence this means:
The Linux kernel’s “no regression” policy holds in practice only for open-source userspace of the DRM subsystem. DRM developers are perfectly fine if closed-source blob drivers in userspace use the same uAPI as the open drivers, but they must do so in the exact same way as the open drivers. Creative (ab)use of the interfaces will, and in the past routinely has, lead to breakage.
Any new userspace interface must have an open-source implementation as demonstration vehicle.
The other reason for requiring open-source userspace is uAPI review. Since the kernel and userspace parts of a GFX stack must work together so closely, code review can only assess whether a new interface achieves its goals by looking at both sides. Making sure that the interface indeed covers the use-case fully leads to a few additional requirements:
The open-source userspace must not be a toy/test application, but the real thing. Specifically it needs to handle all the usual error and corner cases. These are often the places where new uAPI falls apart and hence essential to assess the fitness of a proposed interface.
The userspace side must be fully reviewed and tested to the standards of that userspace project. For e.g. mesa this means piglit testcases and review on the mailing list. This is again to ensure that the new interface actually gets the job done. The userspace-side reviewer should also provide an Acked-by on the kernel uAPI patch indicating that they believe the proposed uAPI is sound and sufficiently documented and validated for userspace’s consumption.
The userspace patches must be against the canonical upstream, not some vendor fork. This is to make sure that no one cheats on the review and testing requirements by doing a quick fork.
The kernel patch can only be merged after all the above requirements are met, but it must be merged to either drm-next or drm-misc-next before the userspace patches land. uAPI always flows from the kernel, doing things the other way round risks divergence of the uAPI definitions and header files.
These are fairly steep requirements, but have grown out from years of shared pain and experience with uAPI added hastily, and almost always regretted about just as fast. GFX devices change really fast, requiring a paradigm shift and entire new set of uAPI interfaces every few years at least. Together with the Linux kernel’s guarantee to keep existing userspace running for 10+ years this is already rather painful for the DRM subsystem, with multiple different uAPIs for the same thing co-existing. If we add a few more complete mistakes into the mix every year it would be entirely unmanageable.
Render nodes¶
DRM core provides multiple character-devices for user-space to use. Depending on which device is opened, user-space can perform a different set of operations (mainly ioctls). The primary node is always created and called card<num>. Additionally, a currently unused control node, called controlD<num> is also created. The primary node provides all legacy operations and historically was the only interface used by userspace. With KMS, the control node was introduced. However, the planned KMS control interface has never been written and so the control node stays unused to date.
With the increased use of offscreen renderers and GPGPU applications, clients no longer require running compositors or graphics servers to make use of a GPU. But the DRM API required unprivileged clients to authenticate to a DRM-Master prior to getting GPU access. To avoid this step and to grant clients GPU access without authenticating, render nodes were introduced. Render nodes solely serve render clients, that is, no modesetting or privileged ioctls can be issued on render nodes. Only non-global rendering commands are allowed. If a driver supports render nodes, it must advertise it via the DRIVER_RENDER DRM driver capability. If not supported, the primary node must be used for render clients together with the legacy drmAuth authentication procedure.
If a driver advertises render node support, DRM core will create a separate render node called renderD<num>. There will be one render node per device. No ioctls except PRIME-related ioctls will be allowed on this node. Especially GEM_OPEN will be explicitly prohibited. For a complete list of driver-independent ioctls that can be used on render nodes, see the ioctls marked DRM_RENDER_ALLOW in drm_ioctl.c Render nodes are designed to avoid the buffer-leaks, which occur if clients guess the flink names or mmap offsets on the legacy interface. Additionally to this basic interface, drivers must mark their driver-dependent render-only ioctls as DRM_RENDER_ALLOW so render clients can use them. Driver authors must be careful not to allow any privileged ioctls on render nodes.
With render nodes, user-space can now control access to the render node via basic file-system access-modes. A running graphics server which authenticates clients on the privileged primary/legacy node is no longer required. Instead, a client can open the render node and is immediately granted GPU access. Communication between clients (or servers) is done via PRIME. FLINK from render node to legacy node is not supported. New clients must not use the insecure FLINK interface.
Besides dropping all modeset/global ioctls, render nodes also drop the DRM-Master concept. There is no reason to associate render clients with a DRM-Master as they are independent of any graphics server. Besides, they must work without any running master, anyway. Drivers must be able to run without a master object if they support render nodes. If, on the other hand, a driver requires shared state between clients which is visible to user-space and accessible beyond open-file boundaries, they cannot support render nodes.
Device Hot-Unplug¶
Note
The following is the plan. Implementation is not there yet (2020 May).
Graphics devices (display and/or render) may be connected via USB (e.g. display adapters or docking stations) or Thunderbolt (e.g. eGPU). An end user is able to hot-unplug this kind of devices while they are being used, and expects that the very least the machine does not crash. Any damage from hot-unplugging a DRM device needs to be limited as much as possible and userspace must be given the chance to handle it if it wants to. Ideally, unplugging a DRM device still lets a desktop continue to run, but that is going to need explicit support throughout the whole graphics stack: from kernel and userspace drivers, through display servers, via window system protocols, and in applications and libraries.
Other scenarios that should lead to the same are: unrecoverable GPU crash, PCI device disappearing off the bus, or forced unbind of a driver from the physical device.
In other words, from userspace perspective everything needs to keep on working more or less, until userspace stops using the disappeared DRM device and closes it completely. Userspace will learn of the device disappearance from the device removed uevent, ioctls returning ENODEV (or driver-specific ioctls returning driver-specific things), or open() returning ENXIO.
Only after userspace has closed all relevant DRM device and dmabuf file descriptors and removed all mmaps, the DRM driver can tear down its instance for the device that no longer exists. If the same physical device somehow comes back in the mean time, it shall be a new DRM device.
Similar to PIDs, chardev minor numbers are not recycled immediately. A new DRM device always picks the next free minor number compared to the previous one allocated, and wraps around when minor numbers are exhausted.
The goal raises at least the following requirements for the kernel and drivers.
Requirements for KMS UAPI¶
KMS connectors must change their status to disconnected.
Legacy modesets and pageflips, and atomic commits, both real and TEST_ONLY, and any other ioctls either fail with ENODEV or fake success.
Pending non-blocking KMS operations deliver the DRM events userspace is expecting. This applies also to ioctls that faked success.
open() on a device node whose underlying device has disappeared will fail with ENXIO.
Attempting to create a DRM lease on a disappeared DRM device will fail with ENODEV. Existing DRM leases remain and work as listed above.
Requirements for Render and Cross-Device UAPI¶
All GPU jobs that can no longer run must have their fences force-signalled to avoid inflicting hangs on userspace. The associated error code is ENODEV.
Some userspace APIs already define what should happen when the device disappears (OpenGL, GL ES: GL_KHR_robustness; Vulkan: VK_ERROR_DEVICE_LOST; etc.). DRM drivers are free to implement this behaviour the way they see best, e.g. returning failures in driver-specific ioctls and handling those in userspace drivers, or rely on uevents, and so on.
dmabuf which point to memory that has disappeared will either fail to import with ENODEV or continue to be successfully imported if it would have succeeded before the disappearance. See also about memory maps below for already imported dmabufs.
Attempting to import a dmabuf to a disappeared device will either fail with ENODEV or succeed if it would have succeeded without the disappearance.
open() on a device node whose underlying device has disappeared will fail with ENXIO.
Requirements for Memory Maps¶
Memory maps have further requirements that apply to both existing maps and maps created after the device has disappeared. If the underlying memory disappears, the map is created or modified such that reads and writes will still complete successfully but the result is undefined. This applies to both userspace mmap()’d memory and memory pointed to by dmabuf which might be mapped to other devices (cross-device dmabuf imports).
Raising SIGBUS is not an option, because userspace cannot realistically handle it. Signal handlers are global, which makes them extremely difficult to use correctly from libraries like those that Mesa produces. Signal handlers are not composable, you can’t have different handlers for GPU1 and GPU2 from different vendors, and a third handler for mmapped regular files. Threads cause additional pain with signal handling as well.
Device reset¶
The GPU stack is really complex and is prone to errors, from hardware bugs, faulty applications and everything in between the many layers. Some errors require resetting the device in order to make the device usable again. This section describes the expectations for DRM and usermode drivers when a device resets and how to propagate the reset status.
Device resets can not be disabled without tainting the kernel, which can lead to hanging the entire kernel through shrinkers/mmu_notifiers. Userspace role in device resets is to propagate the message to the application and apply any special policy for blocking guilty applications, if any. Corollary is that debugging a hung GPU context require hardware support to be able to preempt such a GPU context while it’s stopped.
Kernel Mode Driver¶
The KMD is responsible for checking if the device needs a reset, and to perform it as needed. Usually a hang is detected when a job gets stuck executing.
Propagation of errors to userspace has proven to be tricky since it goes in
the opposite direction of the usual flow of commands. Because of this vendor
independent error handling was added to the &dma_fence object, this way drivers
can add an error code to their fences before signaling them. See function
dma_fence_set_error()
on how to do this and for examples of error codes to use.
The DRM scheduler also allows setting error codes on all pending fences when hardware submissions are restarted after an reset. Error codes are also forwarded from the hardware fence to the scheduler fence to bubble up errors to the higher levels of the stack and eventually userspace.
Fence errors can be queried by userspace through the generic SYNC_IOC_FILE_INFO IOCTL as well as through driver specific interfaces.
Additional to setting fence errors drivers should also keep track of resets per
context, the DRM scheduler provides the drm_sched_entity_error()
function as
helper for this use case. After a reset, KMD should reject new command
submissions for affected contexts.
User Mode Driver¶
After command submission, UMD should check if the submission was accepted or rejected. After a reset, KMD should reject submissions, and UMD can issue an ioctl to the KMD to check the reset status, and this can be checked more often if the UMD requires it. After detecting a reset, UMD will then proceed to report it to the application using the appropriate API error code, as explained in the section below about robustness.
Robustness¶
The only way to try to keep a graphical API context working after a reset is if it complies with the robustness aspects of the graphical API that it is using.
Graphical APIs provide ways to applications to deal with device resets. However, there is no guarantee that the app will use such features correctly, and a userspace that doesn’t support robust interfaces (like a non-robust OpenGL context or API without any robustness support like libva) leave the robustness handling entirely to the userspace driver. There is no strong community consensus on what the userspace driver should do in that case, since all reasonable approaches have some clear downsides.
OpenGL¶
Apps using OpenGL should use the available robust interfaces, like the
extension GL_ARB_robustness
(or GL_EXT_robustness
for OpenGL ES). This
interface tells if a reset has happened, and if so, all the context state is
considered lost and the app proceeds by creating new ones. There’s no consensus
on what to do to if robustness is not in use.
Vulkan¶
Apps using Vulkan should check for VK_ERROR_DEVICE_LOST
for submissions.
This error code means, among other things, that a device reset has happened and
it needs to recreate the contexts to keep going.
Reporting causes of resets¶
Apart from propagating the reset through the stack so apps can recover, it’s really useful for driver developers to learn more about what caused the reset in the first place. DRM devices should make use of devcoredump to store relevant information about the reset, so this information can be added to user bug reports.
IOCTL Support on Device Nodes¶
First things first, driver private IOCTLs should only be needed for drivers supporting rendering. Kernel modesetting is all standardized, and extended through properties. There are a few exceptions in some existing drivers, which define IOCTL for use by the display DRM master, but they all predate properties.
Now if you do have a render driver you always have to support it through driver private properties. There’s a few steps needed to wire all the things up.
First you need to define the structure for your IOCTL in your driver private
UAPI header in include/uapi/drm/my_driver_drm.h
:
struct my_driver_operation {
u32 some_thing;
u32 another_thing;
};
Please make sure that you follow all the best practices from
Documentation/process/botching-up-ioctls.rst
. Note that drm_ioctl()
automatically zero-extends structures, hence make sure you can add more stuff
at the end, i.e. don’t put a variable sized array there.
Then you need to define your IOCTL number, using one of DRM_IO(), DRM_IOR(), DRM_IOW() or DRM_IOWR(). It must start with the DRM_IOCTL_ prefix:
##define DRM_IOCTL_MY_DRIVER_OPERATION \
DRM_IOW(DRM_COMMAND_BASE, struct my_driver_operation)
DRM driver private IOCTL must be in the range from DRM_COMMAND_BASE to
DRM_COMMAND_END. Finally you need an array of struct drm_ioctl_desc
to wire
up the handlers and set the access rights:
static const struct drm_ioctl_desc my_driver_ioctls[] = {
DRM_IOCTL_DEF_DRV(MY_DRIVER_OPERATION, my_driver_operation,
DRM_AUTH|DRM_RENDER_ALLOW),
};
And then assign this to the drm_driver.ioctls
field in your driver
structure.
See the separate chapter on file operations for how the driver-specific IOCTLs are wired up.
Recommended IOCTL Return Values¶
In theory a driver’s IOCTL callback is only allowed to return very few error codes. In practice it’s good to abuse a few more. This section documents common practice within the DRM subsystem:
- ENOENT:
Strictly this should only be used when a file doesn’t exist e.g. when calling the open() syscall. We reuse that to signal any kind of object lookup failure, e.g. for unknown GEM buffer object handles, unknown KMS object handles and similar cases.
- ENOSPC:
Some drivers use this to differentiate “out of kernel memory” from “out of VRAM”. Sometimes also applies to other limited gpu resources used for rendering (e.g. when you have a special limited compression buffer). Sometimes resource allocation/reservation issues in command submission IOCTLs are also signalled through EDEADLK.
Simply running out of kernel/system memory is signalled through ENOMEM.
- EPERM/EACCES:
Returned for an operation that is valid, but needs more privileges. E.g. root-only or much more common, DRM master-only operations return this when called by unpriviledged clients. There’s no clear difference between EACCES and EPERM.
- ENODEV:
The device is not present anymore or is not yet fully initialized.
- EOPNOTSUPP:
Feature (like PRIME, modesetting, GEM) is not supported by the driver.
- ENXIO:
Remote failure, either a hardware transaction (like i2c), but also used when the exporting driver of a shared dma-buf or fence doesn’t support a feature needed.
- EINTR:
DRM drivers assume that userspace restarts all IOCTLs. Any DRM IOCTL can return EINTR and in such a case should be restarted with the IOCTL parameters left unchanged.
- EIO:
The GPU died and couldn’t be resurrected through a reset. Modesetting hardware failures are signalled through the “link status” connector property.
- EINVAL:
Catch-all for anything that is an invalid argument combination which cannot work.
IOCTL also use other error codes like ETIME, EFAULT, EBUSY, ENOTTY but their usage is in line with the common meanings. The above list tries to just document DRM specific patterns. Note that ENOTTY has the slightly unintuitive meaning of “this IOCTL does not exist”, and is used exactly as such in DRM.
-
drm_ioctl_t¶
Typedef: DRM ioctl function type.
Syntax
typedef int drm_ioctl_t (struct drm_device *dev, void *data, struct drm_file *file_priv)
Parameters
struct drm_device *dev
DRM device inode
void *data
private pointer of the ioctl call
struct drm_file *file_priv
DRM file this ioctl was made on
Description
This is the DRM ioctl typedef. Note that drm_ioctl()
has alrady copied data
into kernel-space, and will also copy it back, depending upon the read/write
settings in the ioctl command code.
-
drm_ioctl_compat_t¶
Typedef: compatibility DRM ioctl function type.
Syntax
typedef int drm_ioctl_compat_t (struct file *filp, unsigned int cmd, unsigned long arg)
Parameters
struct file *filp
file pointer
unsigned int cmd
ioctl command code
unsigned long arg
DRM file this ioctl was made on
Description
Just a typedef to make declaring an array of compatibility handlers easier. New drivers shouldn’t screw up the structure layout for their ioctl structures and hence never need this.
-
enum drm_ioctl_flags¶
DRM ioctl flags
Constants
DRM_AUTH
This is for ioctl which are used for rendering, and require that the file descriptor is either for a render node, or if it’s a legacy/primary node, then it must be authenticated.
DRM_MASTER
This must be set for any ioctl which can change the modeset or display state. Userspace must call the ioctl through a primary node, while it is the active master.
Note that read-only modeset ioctl can also be called by unauthenticated clients, or when a master is not the currently active one.
DRM_ROOT_ONLY
Anything that could potentially wreak a master file descriptor needs to have this flag set. Current that’s only for the SETMASTER and DROPMASTER ioctl, which e.g. logind can call to force a non-behaving master (display compositor) into compliance.
This is equivalent to callers with the SYSADMIN capability.
DRM_RENDER_ALLOW
This is used for all ioctl needed for rendering only, for drivers which support render nodes. This should be all new render drivers, and hence it should be always set for any ioctl with DRM_AUTH set. Note though that read-only query ioctl might have this set, but have not set DRM_AUTH because they do not require authentication.
Description
Various flags that can be set in drm_ioctl_desc.flags
to control how
userspace can use a given ioctl.
-
struct drm_ioctl_desc¶
DRM driver ioctl entry
Definition:
struct drm_ioctl_desc {
unsigned int cmd;
enum drm_ioctl_flags flags;
drm_ioctl_t *func;
const char *name;
};
Members
cmd
ioctl command number, without flags
flags
a bitmask of
enum drm_ioctl_flags
func
handler for this ioctl
name
user-readable name for debug output
Description
For convenience it’s easier to create these using the DRM_IOCTL_DEF_DRV()
macro.
-
DRM_IOCTL_DEF_DRV¶
DRM_IOCTL_DEF_DRV (ioctl, _func, _flags)
helper macro to fill out a
struct drm_ioctl_desc
Parameters
ioctl
ioctl command suffix
_func
handler for the ioctl
_flags
a bitmask of
enum drm_ioctl_flags
Description
Small helper macro to create a struct drm_ioctl_desc
entry. The ioctl
command number is constructed by prepending DRM_IOCTL\_
and passing that
to DRM_IOCTL_NR().
-
int drm_noop(struct drm_device *dev, void *data, struct drm_file *file_priv)¶
DRM no-op ioctl implementation
Parameters
struct drm_device *dev
DRM device for the ioctl
void *data
data pointer for the ioctl
struct drm_file *file_priv
DRM file for the ioctl call
Description
This no-op implementation for drm ioctls is useful for deprecated functionality where we can’t return a failure code because existing userspace checks the result of the ioctl, but doesn’t care about the action.
Always returns successfully with 0.
-
int drm_invalid_op(struct drm_device *dev, void *data, struct drm_file *file_priv)¶
DRM invalid ioctl implementation
Parameters
struct drm_device *dev
DRM device for the ioctl
void *data
data pointer for the ioctl
struct drm_file *file_priv
DRM file for the ioctl call
Description
This no-op implementation for drm ioctls is useful for deprecated functionality where we really don’t want to allow userspace to call the ioctl any more. This is the case for old ums interfaces for drivers that transitioned to kms gradually and so kept the old legacy tables around. This only applies to radeon and i915 kms drivers, other drivers shouldn’t need to use this function.
Always fails with a return value of -EINVAL.
-
long drm_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)¶
ioctl callback implementation for DRM drivers
Parameters
struct file *filp
file this ioctl is called on
unsigned int cmd
ioctl cmd number
unsigned long arg
user argument
Description
Looks up the ioctl function in the DRM core and the driver dispatch table,
stored in drm_driver.ioctls
. It checks for necessary permission by calling
drm_ioctl_permit(), and dispatches to the respective function.
Return
Zero on success, negative error code on failure.
-
bool drm_ioctl_flags(unsigned int nr, unsigned int *flags)
Check for core ioctl and return ioctl permission flags
Parameters
unsigned int nr
ioctl number
unsigned int *flags
where to return the ioctl permission flags
Description
This ioctl is only used by the vmwgfx driver to augment the access checks done by the drm core and insofar a pretty decent layering violation. This shouldn’t be used by any drivers.
Return
True if the nr corresponds to a DRM core ioctl number, false otherwise.
-
long drm_compat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)¶
32bit IOCTL compatibility handler for DRM drivers
Parameters
struct file *filp
file this ioctl is called on
unsigned int cmd
ioctl cmd number
unsigned long arg
user argument
Description
Compatibility handler for 32 bit userspace running on 64 kernels. All actual
IOCTL handling is forwarded to drm_ioctl()
, while marshalling structures as
appropriate. Note that this only handles DRM core IOCTLs, if the driver has
botched IOCTL itself, it must handle those by wrapping this function.
Return
Zero on success, negative error code on failure.
Testing and validation¶
Testing Requirements for userspace API¶
New cross-driver userspace interface extensions, like new IOCTL, new KMS properties, new files in sysfs or anything else that constitutes an API change should have driver-agnostic testcases in IGT for that feature, if such a test can be reasonably made using IGT for the target hardware.
Validating changes with IGT¶
There’s a collection of tests that aims to cover the whole functionality of DRM drivers and that can be used to check that changes to DRM drivers or the core don’t regress existing functionality. This test suite is called IGT and its code and instructions to build and run can be found in https://gitlab.freedesktop.org/drm/igt-gpu-tools/.
Using VKMS to test DRM API¶
VKMS is a software-only model of a KMS driver that is useful for testing and for running compositors. VKMS aims to enable a virtual display without the need for a hardware display capability. These characteristics made VKMS a perfect tool for validating the DRM core behavior and also support the compositor developer. VKMS makes it possible to test DRM functions in a virtual machine without display, simplifying the validation of some of the core changes.
To Validate changes in DRM API with VKMS, start setting the kernel: make sure to enable VKMS module; compile the kernel with the VKMS enabled and install it in the target machine. VKMS can be run in a Virtual Machine (QEMU, virtme or similar). It’s recommended the use of KVM with the minimum of 1GB of RAM and four cores.
It’s possible to run the IGT-tests in a VM in two ways:
Use IGT inside a VM
Use IGT from the host machine and write the results in a shared directory.
Following is an example of using a VM with a shared directory with the host machine to run igt-tests. This example uses virtme:
$ virtme-run --rwdir /path/for/shared_dir --kdir=path/for/kernel/directory --mods=auto
Run the igt-tests in the guest machine. This example runs the ‘kms_flip’ tests:
$ /path/for/igt-gpu-tools/scripts/run-tests.sh -p -s -t "kms_flip.*" -v
In this example, instead of building the igt_runner, Piglit is used (-p option). It creates an HTML summary of the test results and saves them in the folder “igt-gpu-tools/results”. It executes only the igt-tests matching the -t option.
Display CRC Support¶
DRM device drivers can provide to userspace CRC information of each frame as it reached a given hardware component (a CRC sampling “source”).
Userspace can control generation of CRCs in a given CRTC by writing to the file dri/0/crtc-N/crc/control in debugfs, with N being the index of the CRTC. Accepted values are source names (which are driver-specific) and the “auto” keyword, which will let the driver select a default source of frame CRCs for this CRTC.
Once frame CRC generation is enabled, userspace can capture them by reading the dri/0/crtc-N/crc/data file. Each line in that file contains the frame number in the first field and then a number of unsigned integer fields containing the CRC data. Fields are separated by a single space and the number of CRC fields is source-specific.
Note that though in some cases the CRC is computed in a specified way and on the frame contents as supplied by userspace (eDP 1.3), in general the CRC computation is performed in an unspecified way and on frame contents that have been already processed in also an unspecified way and thus userspace cannot rely on being able to generate matching CRC values for the frame contents that it submits. In this general case, the maximum userspace can do is to compare the reported CRCs of frames that should have the same contents.
On the driver side the implementation effort is minimal, drivers only need to
implement drm_crtc_funcs.set_crc_source
and drm_crtc_funcs.verify_crc_source
.
The debugfs files are automatically set up if those vfuncs are set. CRC samples
need to be captured in the driver by calling drm_crtc_add_crc_entry()
.
Depending on the driver and HW requirements, drm_crtc_funcs.set_crc_source
may result in a commit (even a full modeset).
CRC results must be reliable across non-full-modeset atomic commits, so if a
commit via DRM_IOCTL_MODE_ATOMIC would disable or otherwise interfere with
CRC generation, then the driver must mark that commit as a full modeset
(drm_atomic_crtc_needs_modeset()
should return true). As a result, to ensure
consistent results, generic userspace must re-setup CRC generation after a
legacy SETCRTC or an atomic commit with DRM_MODE_ATOMIC_ALLOW_MODESET.
-
int drm_crtc_add_crc_entry(struct drm_crtc *crtc, bool has_frame, uint32_t frame, uint32_t *crcs)¶
Add entry with CRC information for a frame
Parameters
struct drm_crtc *crtc
CRTC to which the frame belongs
bool has_frame
whether this entry has a frame number to go with
uint32_t frame
number of the frame these CRCs are about
uint32_t *crcs
array of CRC values, with length matching #drm_crtc_crc.values_cnt
Description
For each frame, the driver polls the source of CRCs for new data and calls this function to add them to the buffer from where userspace reads.
Debugfs Support¶
-
DRM_DEBUGFS_GPUVA_INFO¶
DRM_DEBUGFS_GPUVA_INFO (show, data)
drm_info_list
entry to dump a GPU VA space
Parameters
show
the
drm_info_list
’s show callbackdata
driver private data
Description
Drivers should use this macro to define a drm_info_list
entry to provide a
debugfs file for dumping the GPU VA space regions and mappings.
For each DRM GPU VA space drivers should call drm_debugfs_gpuva_info()
from
their show callback.
-
struct drm_info_list¶
debugfs info list entry
Definition:
struct drm_info_list {
const char *name;
int (*show)(struct seq_file*, void*);
u32 driver_features;
void *data;
};
Members
name
file name
show
Show callback.
seq_file->private
will be set to thestruct drm_info_node
corresponding to the instance of this info on a givenstruct drm_minor
.driver_features
Required driver features for this entry
data
Driver-private data, should not be device-specific.
Description
This structure represents a debugfs file to be created by the drm core.
-
struct drm_info_node¶
Per-minor debugfs node structure
Definition:
struct drm_info_node {
struct drm_minor *minor;
const struct drm_info_list *info_ent;
};
Members
minor
struct drm_minor
for this node.info_ent
template for this node.
Description
This structure represents a debugfs file, as an instantiation of a struct
drm_info_list
on a struct drm_minor
.
FIXME:
No it doesn’t make a hole lot of sense that we duplicate debugfs entries for both the render and the primary nodes, but that’s how this has organically grown. It should probably be fixed, with a compatibility link, if needed.
-
struct drm_debugfs_info¶
debugfs info list entry
Definition:
struct drm_debugfs_info {
const char *name;
int (*show)(struct seq_file*, void*);
u32 driver_features;
void *data;
};
Members
name
File name
show
Show callback.
seq_file->private
will be set to thestruct drm_debugfs_entry
corresponding to the instance of this info on a givenstruct drm_device
.driver_features
Required driver features for this entry.
data
Driver-private data, should not be device-specific.
Description
This structure represents a debugfs file to be created by the drm core.
-
struct drm_debugfs_entry¶
Per-device debugfs node structure
Definition:
struct drm_debugfs_entry {
struct drm_device *dev;
struct drm_debugfs_info file;
struct list_head list;
};
Members
dev
struct drm_device
for this node.file
Template for this node.
list
Linked list of all device nodes.
Description
This structure represents a debugfs file, as an instantiation of a struct
drm_debugfs_info
on a struct drm_device
.
-
int drm_debugfs_gpuva_info(struct seq_file *m, struct drm_gpuvm *gpuvm)¶
dump the given DRM GPU VA space
Parameters
struct seq_file *m
pointer to the
seq_file
to writestruct drm_gpuvm *gpuvm
the
drm_gpuvm
representing the GPU VA space
Description
Dumps the GPU VA mappings of a given DRM GPU VA manager.
For each DRM GPU VA space drivers should call this function from their
drm_info_list
’s show callback.
Return
0 on success, -ENODEV if the gpuvm
is not initialized
-
void drm_debugfs_create_files(const struct drm_info_list *files, int count, struct dentry *root, struct drm_minor *minor)¶
Initialize a given set of debugfs files for DRM minor
Parameters
const struct drm_info_list *files
The array of files to create
int count
The number of files given
struct dentry *root
DRI debugfs dir entry.
struct drm_minor *minor
device minor number
Description
Create a given set of debugfs files represented by an array of
struct drm_info_list
in the given root directory. These files will be removed
automatically on drm_debugfs_dev_fini().
-
void drm_debugfs_add_file(struct drm_device *dev, const char *name, int (*show)(struct seq_file*, void*), void *data)¶
Add a given file to the DRM device debugfs file list
Parameters
struct drm_device *dev
drm device for the ioctl
const char *name
debugfs file name
int (*show)(struct seq_file*, void*)
show callback
void *data
driver-private data, should not be device-specific
Description
Add a given file entry to the DRM device debugfs file list to be created on drm_debugfs_init.
-
void drm_debugfs_add_files(struct drm_device *dev, const struct drm_debugfs_info *files, int count)¶
Add an array of files to the DRM device debugfs file list
Parameters
struct drm_device *dev
drm device for the ioctl
const struct drm_debugfs_info *files
The array of files to create
int count
The number of files given
Description
Add a given set of debugfs files represented by an array of
struct drm_debugfs_info
in the DRM device debugfs file list.
Sysfs Support¶
DRM provides very little additional support to drivers for sysfs
interactions, beyond just all the standard stuff. Drivers who want to expose
additional sysfs properties and property groups can attach them at either
drm_device.dev
or drm_connector.kdev
.
Registration is automatically handled when calling drm_dev_register()
, or
drm_connector_register()
in case of hot-plugged connectors. Unregistration is
also automatically handled by drm_dev_unregister()
and
drm_connector_unregister()
.
-
void drm_sysfs_hotplug_event(struct drm_device *dev)¶
generate a DRM uevent
Parameters
struct drm_device *dev
DRM device
Description
Send a uevent for the DRM device specified by dev. Currently we only set HOTPLUG=1 in the uevent environment, but this could be expanded to deal with other types of events.
Any new uapi should be using the drm_sysfs_connector_status_event() for uevents on connector status change.
-
void drm_sysfs_connector_hotplug_event(struct drm_connector *connector)¶
generate a DRM uevent for any connector change
Parameters
struct drm_connector *connector
connector which has changed
Description
Send a uevent for the DRM connector specified by connector. This will send a uevent with the properties HOTPLUG=1 and CONNECTOR.
-
void drm_sysfs_connector_property_event(struct drm_connector *connector, struct drm_property *property)¶
generate a DRM uevent for connector property change
Parameters
struct drm_connector *connector
connector on which property changed
struct drm_property *property
connector property which has changed.
Description
Send a uevent for the specified DRM connector and property. Currently we set HOTPLUG=1 and connector id along with the attached property id related to the change.
Parameters
struct device *dev
device to register
Description
Registers a new struct device
within the DRM sysfs class. Essentially only
used by ttm to have a place for its global settings. Drivers should never use
this.
Parameters
struct device *dev
device to unregister
Description
Unregisters a struct device
from the DRM sysfs class. Essentially only used
by ttm to have a place for its global settings. Drivers should never use
this.
VBlank event handling¶
The DRM core exposes two vertical blank related ioctls:
DRM_IOCTL_WAIT_VBLANK
This takes a struct drm_wait_vblank structure as its argument, and it is used to block or request a signal when a specified vblank event occurs.
DRM_IOCTL_MODESET_CTL
This was only used for user-mode-settind drivers around modesetting changes to allow the kernel to update the vblank interrupt after mode setting, since on many devices the vertical blank counter is reset to 0 at some point during modeset. Modern drivers should not call this any more since with kernel mode setting it is a no-op.
Userspace API Structures¶
DRM exposes many UAPI and structure definitions to have a consistent and standardized interface with users. Userspace can refer to these structure definitions and UAPI formats to communicate to drivers.
CRTC index¶
CRTC’s have both an object ID and an index, and they are not the same thing.
The index is used in cases where a densely packed identifier for a CRTC is
needed, for instance a bitmask of CRTC’s. The member possible_crtcs of struct
drm_mode_get_plane
is an example.
DRM_IOCTL_MODE_GETRESOURCES
populates a structure with an array of
CRTC ID’s, and the CRTC index is its position in this array.
-
DRM_CAP_DUMB_BUFFER¶
DRM_CAP_DUMB_BUFFER
Description
If set to 1, the driver supports creating dumb buffers via the
DRM_IOCTL_MODE_CREATE_DUMB
ioctl.
-
DRM_CAP_VBLANK_HIGH_CRTC¶
DRM_CAP_VBLANK_HIGH_CRTC
Description
If set to 1, the kernel supports specifying a CRTC index in the high bits of
drm_wait_vblank_request.type
.Starting kernel version 2.6.39, this capability is always set to 1.
-
DRM_CAP_DUMB_PREFERRED_DEPTH¶
DRM_CAP_DUMB_PREFERRED_DEPTH
Description
The preferred bit depth for dumb buffers.
The bit depth is the number of bits used to indicate the color of a single pixel excluding any padding. This is different from the number of bits per pixel. For instance, XRGB8888 has a bit depth of 24 but has 32 bits per pixel.
Note that this preference only applies to dumb buffers, it’s irrelevant for other types of buffers.
-
DRM_CAP_DUMB_PREFER_SHADOW¶
DRM_CAP_DUMB_PREFER_SHADOW
Description
If set to 1, the driver prefers userspace to render to a shadow buffer instead of directly rendering to a dumb buffer. For best speed, userspace should do streaming ordered memory copies into the dumb buffer and never read from it.
Note that this preference only applies to dumb buffers, it’s irrelevant for other types of buffers.
-
DRM_CAP_PRIME¶
DRM_CAP_PRIME
Description
Bitfield of supported PRIME sharing capabilities. See
DRM_PRIME_CAP_IMPORT
andDRM_PRIME_CAP_EXPORT
.Starting from kernel version 6.6, both
DRM_PRIME_CAP_IMPORT
andDRM_PRIME_CAP_EXPORT
are always advertised.PRIME buffers are exposed as dma-buf file descriptors. See PRIME Buffer Sharing.
-
DRM_PRIME_CAP_IMPORT¶
DRM_PRIME_CAP_IMPORT
Description
If this bit is set in
DRM_CAP_PRIME
, the driver supports importing PRIME buffers via theDRM_IOCTL_PRIME_FD_TO_HANDLE
ioctl.Starting from kernel version 6.6, this bit is always set in
DRM_CAP_PRIME
.
-
DRM_PRIME_CAP_EXPORT¶
DRM_PRIME_CAP_EXPORT
Description
If this bit is set in
DRM_CAP_PRIME
, the driver supports exporting PRIME buffers via theDRM_IOCTL_PRIME_HANDLE_TO_FD
ioctl.Starting from kernel version 6.6, this bit is always set in
DRM_CAP_PRIME
.
-
DRM_CAP_TIMESTAMP_MONOTONIC¶
DRM_CAP_TIMESTAMP_MONOTONIC
Description
If set to 0, the kernel will report timestamps with
CLOCK_REALTIME
in struct drm_event_vblank. If set to 1, the kernel will report timestamps withCLOCK_MONOTONIC
. Seeclock_gettime(2)
for the definition of these clocks.Starting from kernel version 2.6.39, the default value for this capability is 1. Starting kernel version 4.15, this capability is always set to 1.
-
DRM_CAP_ASYNC_PAGE_FLIP¶
DRM_CAP_ASYNC_PAGE_FLIP
Description
If set to 1, the driver supports
DRM_MODE_PAGE_FLIP_ASYNC
for legacy page-flips.
-
DRM_CAP_CURSOR_WIDTH¶
DRM_CAP_CURSOR_WIDTH
Description
The
CURSOR_WIDTH
andCURSOR_HEIGHT
capabilities return a valid width x height combination for the hardware cursor. The intention is that a hardware agnostic userspace can query a cursor plane size to use.Note that the cross-driver contract is to merely return a valid size; drivers are free to attach another meaning on top, eg. i915 returns the maximum plane size.
-
DRM_CAP_CURSOR_HEIGHT¶
DRM_CAP_CURSOR_HEIGHT
Description
See
DRM_CAP_CURSOR_WIDTH
.
-
DRM_CAP_ADDFB2_MODIFIERS¶
DRM_CAP_ADDFB2_MODIFIERS
Description
If set to 1, the driver supports supplying modifiers in the
DRM_IOCTL_MODE_ADDFB2
ioctl.
-
DRM_CAP_PAGE_FLIP_TARGET¶
DRM_CAP_PAGE_FLIP_TARGET
Description
If set to 1, the driver supports the
DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE
andDRM_MODE_PAGE_FLIP_TARGET_RELATIVE
flags indrm_mode_crtc_page_flip_target.flags
for theDRM_IOCTL_MODE_PAGE_FLIP
ioctl.
-
DRM_CAP_CRTC_IN_VBLANK_EVENT¶
DRM_CAP_CRTC_IN_VBLANK_EVENT
Description
If set to 1, the kernel supports reporting the CRTC ID in
drm_event_vblank.crtc_id
for theDRM_EVENT_VBLANK
andDRM_EVENT_FLIP_COMPLETE
events.Starting kernel version 4.12, this capability is always set to 1.
-
DRM_CAP_SYNCOBJ¶
DRM_CAP_SYNCOBJ
Description
If set to 1, the driver supports sync objects. See DRM Sync Objects.
-
DRM_CAP_SYNCOBJ_TIMELINE¶
DRM_CAP_SYNCOBJ_TIMELINE
Description
If set to 1, the driver supports timeline operations on sync objects. See DRM Sync Objects.
-
DRM_CAP_ATOMIC_ASYNC_PAGE_FLIP¶
DRM_CAP_ATOMIC_ASYNC_PAGE_FLIP
Description
If set to 1, the driver supports
DRM_MODE_PAGE_FLIP_ASYNC
for atomic commits.
-
DRM_CLIENT_CAP_STEREO_3D¶
DRM_CLIENT_CAP_STEREO_3D
Description
If set to 1, the DRM core will expose the stereo 3D capabilities of the monitor by advertising the supported 3D layouts in the flags of
struct drm_mode_modeinfo
. SeeDRM_MODE_FLAG_3D_*
.This capability is always supported for all drivers starting from kernel version 3.13.
-
DRM_CLIENT_CAP_UNIVERSAL_PLANES¶
DRM_CLIENT_CAP_UNIVERSAL_PLANES
Description
If set to 1, the DRM core will expose all planes (overlay, primary, and cursor) to userspace.
This capability has been introduced in kernel version 3.15. Starting from kernel version 3.17, this capability is always supported for all drivers.
-
DRM_CLIENT_CAP_ATOMIC¶
DRM_CLIENT_CAP_ATOMIC
Description
If set to 1, the DRM core will expose atomic properties to userspace. This implicitly enables
DRM_CLIENT_CAP_UNIVERSAL_PLANES
andDRM_CLIENT_CAP_ASPECT_RATIO
.If the driver doesn’t support atomic mode-setting, enabling this capability will fail with -EOPNOTSUPP.
This capability has been introduced in kernel version 4.0. Starting from kernel version 4.2, this capability is always supported for atomic-capable drivers.
-
DRM_CLIENT_CAP_ASPECT_RATIO¶
DRM_CLIENT_CAP_ASPECT_RATIO
Description
If set to 1, the DRM core will provide aspect ratio information in modes. See
DRM_MODE_FLAG_PIC_AR_*
.This capability is always supported for all drivers starting from kernel version 4.18.
-
DRM_CLIENT_CAP_WRITEBACK_CONNECTORS¶
DRM_CLIENT_CAP_WRITEBACK_CONNECTORS
Description
If set to 1, the DRM core will expose special connectors to be used for writing back to memory the scene setup in the commit. The client must enable
DRM_CLIENT_CAP_ATOMIC
first.This capability is always supported for atomic-capable drivers starting from kernel version 4.19.
-
DRM_CLIENT_CAP_CURSOR_PLANE_HOTSPOT¶
DRM_CLIENT_CAP_CURSOR_PLANE_HOTSPOT
Description
Drivers for para-virtualized hardware (e.g. vmwgfx, qxl, virtio and virtualbox) have additional restrictions for cursor planes (thus making cursor planes on those drivers not truly universal,) e.g. they need cursor planes to act like one would expect from a mouse cursor and have correctly set hotspot properties. If this client cap is not set the DRM core will hide cursor plane on those virtualized drivers because not setting it implies that the client is not capable of dealing with those extra restictions. Clients which do set cursor hotspot and treat the cursor plane like a mouse cursor should set this property. The client must enable
DRM_CLIENT_CAP_ATOMIC
first.Setting this property on drivers which do not special case cursor planes (i.e. non-virtualized drivers) will return EOPNOTSUPP, which can be used by userspace to gauge requirements of the hardware/drivers they’re running on.
This capability is always supported for atomic-capable virtualized drivers starting from kernel version 6.6.
-
struct drm_syncobj_eventfd¶
Definition:
struct drm_syncobj_eventfd {
__u32 handle;
__u32 flags;
__u64 point;
__s32 fd;
__u32 pad;
};
Members
handle
syncobj handle.
flags
Zero to wait for the point to be signalled, or
DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE
to wait for a fence to be available for the point.point
syncobj timeline point (set to zero for binary syncobjs).
fd
Existing eventfd to sent events to.
pad
Must be zero.
Description
Register an eventfd to be signalled by a syncobj. The eventfd counter will be incremented by one.
-
DRM_IOCTL_GEM_CLOSE¶
DRM_IOCTL_GEM_CLOSE
Close a GEM handle.
Description
GEM handles are not reference-counted by the kernel. User-space is responsible for managing their lifetime. For example, if user-space imports the same memory object twice on the same DRM file description, the same GEM handle is returned by both imports, and user-space needs to ensure
DRM_IOCTL_GEM_CLOSE
is performed once only. The same situation can happen when a memory object is allocated, then exported and imported again on the same DRM file description. TheDRM_IOCTL_MODE_GETFB2
IOCTL is an exception and always returns fresh new GEM handles even if an existing GEM handle already refers to the same memory object before the IOCTL is performed.
-
DRM_IOCTL_PRIME_HANDLE_TO_FD¶
DRM_IOCTL_PRIME_HANDLE_TO_FD
Convert a GEM handle to a DMA-BUF FD.
Description
User-space sets
drm_prime_handle.handle
with the GEM handle to export anddrm_prime_handle.flags
, and gets back a DMA-BUF file descriptor indrm_prime_handle.fd
.The export can fail for any driver-specific reason, e.g. because export is not supported for this specific GEM handle (but might be for others).
Support for exporting DMA-BUFs is advertised via
DRM_PRIME_CAP_EXPORT
.
-
DRM_IOCTL_PRIME_FD_TO_HANDLE¶
DRM_IOCTL_PRIME_FD_TO_HANDLE
Convert a DMA-BUF FD to a GEM handle.
Description
User-space sets
drm_prime_handle.fd
with a DMA-BUF file descriptor to import, and gets back a GEM handle indrm_prime_handle.handle
.drm_prime_handle.flags
is unused.If an existing GEM handle refers to the memory object backing the DMA-BUF, that GEM handle is returned. Therefore user-space which needs to handle arbitrary DMA-BUFs must have a user-space lookup data structure to manually reference-count duplicated GEM handles. For more information see
DRM_IOCTL_GEM_CLOSE
.The import can fail for any driver-specific reason, e.g. because import is only supported for DMA-BUFs allocated on this DRM device.
Support for importing DMA-BUFs is advertised via
DRM_PRIME_CAP_IMPORT
.
-
DRM_IOCTL_MODE_RMFB¶
DRM_IOCTL_MODE_RMFB
Remove a framebuffer.
Description
This removes a framebuffer previously added via ADDFB/ADDFB2. The IOCTL argument is a framebuffer object ID.
Warning: removing a framebuffer currently in-use on an enabled plane will disable that plane. The CRTC the plane is linked to may also be disabled (depending on driver capabilities).
-
DRM_IOCTL_MODE_CREATE_DUMB¶
DRM_IOCTL_MODE_CREATE_DUMB
Create a new dumb buffer object.
Description
KMS dumb buffers provide a very primitive way to allocate a buffer object suitable for scanout and map it for software rendering. KMS dumb buffers are not suitable for hardware-accelerated rendering nor video decoding. KMS dumb buffers are not suitable to be displayed on any other device than the KMS device where they were allocated from. Also see Dumb Buffer Objects.
The IOCTL argument is a
struct drm_mode_create_dumb
.User-space is expected to create a KMS dumb buffer via this IOCTL, then add it as a KMS framebuffer via
DRM_IOCTL_MODE_ADDFB
and map it viaDRM_IOCTL_MODE_MAP_DUMB
.
DRM_CAP_DUMB_BUFFER
indicates whether this IOCTL is supported.DRM_CAP_DUMB_PREFERRED_DEPTH
andDRM_CAP_DUMB_PREFER_SHADOW
indicate driver preferences for dumb buffers.
-
DRM_IOCTL_MODE_GETFB2¶
DRM_IOCTL_MODE_GETFB2
Get framebuffer metadata.
Description
This queries metadata about a framebuffer. User-space fills
drm_mode_fb_cmd2.fb_id
as the input, and the kernels fills the rest of the struct as the output.If the client is DRM master or has
CAP_SYS_ADMIN
,drm_mode_fb_cmd2.handles
will be filled with GEM buffer handles. Fresh new GEM handles are always returned, even if another GEM handle referring to the same memory object already exists on the DRM file description. The caller is responsible for removing the new handles, e.g. via theDRM_IOCTL_GEM_CLOSE
IOCTL. The same new handle will be returned for multiple planes in case they use the same memory object. Planes are valid until one has a zero handle -- this can be used to compute the number of planes.Otherwise,
drm_mode_fb_cmd2.handles
will be zeroed and planes are valid until one has a zerodrm_mode_fb_cmd2.pitches
.If the framebuffer has a format modifier,
DRM_MODE_FB_MODIFIERS
will be set indrm_mode_fb_cmd2.flags
anddrm_mode_fb_cmd2.modifier
will contain the modifier. Otherwise, user-space must ignoredrm_mode_fb_cmd2.modifier
.To obtain DMA-BUF FDs for each plane without leaking GEM handles, user-space can export each handle via
DRM_IOCTL_PRIME_HANDLE_TO_FD
, then immediately close each unique handle viaDRM_IOCTL_GEM_CLOSE
, making sure to not double-close handles which are specified multiple times in the array.
-
DRM_IOCTL_MODE_CLOSEFB¶
DRM_IOCTL_MODE_CLOSEFB
Close a framebuffer.
Description
This closes a framebuffer previously added via ADDFB/ADDFB2. The IOCTL argument is a framebuffer object ID.
This IOCTL is similar to
DRM_IOCTL_MODE_RMFB
, except it doesn’t disable planes and CRTCs. As long as the framebuffer is used by a plane, it’s kept alive. When the plane no longer uses the framebuffer (because the framebuffer is replaced with another one, or the plane is disabled), the framebuffer is cleaned up.This is useful to implement flicker-free transitions between two processes.
Depending on the threat model, user-space may want to ensure that the framebuffer doesn’t expose any sensitive user information: closed framebuffers attached to a plane can be read back by the next DRM master.
-
DRM_IOCTL_SET_CLIENT_NAME¶
DRM_IOCTL_SET_CLIENT_NAME
Attach a name to a drm_file
Description
Having a name allows for easier tracking and debugging. The length of the name (without null ending char) must be <= DRM_CLIENT_NAME_MAX_LEN. The call will fail if the name contains whitespaces or non-printable chars.
-
struct drm_event¶
Header for DRM events
Definition:
struct drm_event {
__u32 type;
__u32 length;
};
Members
type
event type.
length
total number of payload bytes (including header).
Description
This struct is a header for events written back to user-space on the DRM FD. A read on the DRM FD will always only return complete events: e.g. if the read buffer is 100 bytes large and there are two 64 byte events pending, only one will be returned.
Event types 0 - 0x7fffffff are generic DRM events, 0x80000000 and
up are chipset specific. Generic DRM events include DRM_EVENT_VBLANK
,
DRM_EVENT_FLIP_COMPLETE
and DRM_EVENT_CRTC_SEQUENCE
.
-
DRM_EVENT_VBLANK¶
DRM_EVENT_VBLANK
vertical blanking event
Description
This event is sent in response to
DRM_IOCTL_WAIT_VBLANK
with the_DRM_VBLANK_EVENT
flag set.The event payload is a struct drm_event_vblank.
-
DRM_EVENT_FLIP_COMPLETE¶
DRM_EVENT_FLIP_COMPLETE
page-flip completion event
Description
This event is sent in response to an atomic commit or legacy page-flip with the
DRM_MODE_PAGE_FLIP_EVENT
flag set.The event payload is a struct drm_event_vblank.
-
DRM_EVENT_CRTC_SEQUENCE¶
DRM_EVENT_CRTC_SEQUENCE
CRTC sequence event
Description
This event is sent in response to
DRM_IOCTL_CRTC_QUEUE_SEQUENCE
.The event payload is a struct drm_event_crtc_sequence.
-
struct drm_mode_modeinfo¶
Display mode information.
Definition:
struct drm_mode_modeinfo {
__u32 clock;
__u16 hdisplay;
__u16 hsync_start;
__u16 hsync_end;
__u16 htotal;
__u16 hskew;
__u16 vdisplay;
__u16 vsync_start;
__u16 vsync_end;
__u16 vtotal;
__u16 vscan;
__u32 vrefresh;
__u32 flags;
__u32 type;
char name[DRM_DISPLAY_MODE_LEN];
};
Members
clock
pixel clock in kHz
hdisplay
horizontal display size
hsync_start
horizontal sync start
hsync_end
horizontal sync end
htotal
horizontal total size
hskew
horizontal skew
vdisplay
vertical display size
vsync_start
vertical sync start
vsync_end
vertical sync end
vtotal
vertical total size
vscan
vertical scan
vrefresh
approximate vertical refresh rate in Hz
flags
bitmask of misc. flags, see DRM_MODE_FLAG_* defines
type
bitmask of type flags, see DRM_MODE_TYPE_* defines
name
string describing the mode resolution
Description
This is the user-space API display mode information structure. For the
kernel version see struct drm_display_mode
.
-
struct drm_mode_get_plane¶
Get plane metadata.
Definition:
struct drm_mode_get_plane {
__u32 plane_id;
__u32 crtc_id;
__u32 fb_id;
__u32 possible_crtcs;
__u32 gamma_size;
__u32 count_format_types;
__u64 format_type_ptr;
};
Members
plane_id
Object ID of the plane whose information should be retrieved. Set by caller.
crtc_id
Object ID of the current CRTC.
fb_id
Object ID of the current fb.
possible_crtcs
Bitmask of CRTC’s compatible with the plane. CRTC’s are created and they receive an index, which corresponds to their position in the bitmask. Bit N corresponds to CRTC index N.
gamma_size
Never used.
count_format_types
Number of formats.
format_type_ptr
Pointer to
__u32
array of formats that are supported by the plane. These formats do not require modifiers.
Description
Userspace can perform a GETPLANE ioctl to retrieve information about a plane.
To retrieve the number of formats supported, set count_format_types to zero and call the ioctl. count_format_types will be updated with the value.
To retrieve these formats, allocate an array with the memory needed to store count_format_types formats. Point format_type_ptr to this array and call the ioctl again (with count_format_types still set to the value returned in the first ioctl call).
-
struct drm_mode_get_connector¶
Get connector metadata.
Definition:
struct drm_mode_get_connector {
__u64 encoders_ptr;
__u64 modes_ptr;
__u64 props_ptr;
__u64 prop_values_ptr;
__u32 count_modes;
__u32 count_props;
__u32 count_encoders;
__u32 encoder_id;
__u32 connector_id;
__u32 connector_type;
__u32 connector_type_id;
__u32 connection;
__u32 mm_width;
__u32 mm_height;
__u32 subpixel;
__u32 pad;
};
Members
encoders_ptr
Pointer to
__u32
array of object IDs.modes_ptr
Pointer to
struct drm_mode_modeinfo
array.props_ptr
Pointer to
__u32
array of property IDs.prop_values_ptr
Pointer to
__u64
array of property values.count_modes
Number of modes.
count_props
Number of properties.
count_encoders
Number of encoders.
encoder_id
Object ID of the current encoder.
connector_id
Object ID of the connector.
connector_type
Type of the connector.
See DRM_MODE_CONNECTOR_* defines.
connector_type_id
Type-specific connector number.
This is not an object ID. This is a per-type connector number. Each (type, type_id) combination is unique across all connectors of a DRM device.
The (type, type_id) combination is not a stable identifier: the type_id can change depending on the driver probe order.
connection
Status of the connector.
mm_width
Width of the connected sink in millimeters.
mm_height
Height of the connected sink in millimeters.
subpixel
Subpixel order of the connected sink.
See enum subpixel_order.
pad
Padding, must be zero.
Description
User-space can perform a GETCONNECTOR ioctl to retrieve information about a connector. User-space is expected to retrieve encoders, modes and properties by performing this ioctl at least twice: the first time to retrieve the number of elements, the second time to retrieve the elements themselves.
To retrieve the number of elements, set count_props and count_encoders to
zero, set count_modes to 1, and set modes_ptr to a temporary struct
drm_mode_modeinfo
element.
To retrieve the elements, allocate arrays for encoders_ptr, modes_ptr, props_ptr and prop_values_ptr, then set count_modes, count_props and count_encoders to their capacity.
Performing the ioctl only twice may be racy: the number of elements may have changed with a hotplug event in-between the two ioctls. User-space is expected to retry the last ioctl until the number of elements stabilizes. The kernel won’t fill any array which doesn’t have the expected length.
Force-probing a connector
If the count_modes field is set to zero and the DRM client is the current DRM master, the kernel will perform a forced probe on the connector to refresh the connector status, modes and EDID. A forced-probe can be slow, might cause flickering and the ioctl will block.
User-space needs to force-probe connectors to ensure their metadata is up-to-date at startup and after receiving a hot-plug event. User-space may perform a forced-probe when the user explicitly requests it. User-space shouldn’t perform a forced-probe in other situations.
-
struct drm_mode_property_enum¶
Description for an enum/bitfield entry.
Definition:
struct drm_mode_property_enum {
__u64 value;
char name[DRM_PROP_NAME_LEN];
};
Members
value
numeric value for this enum entry.
name
symbolic name for this enum entry.
Description
See struct drm_property_enum
for details.
-
struct drm_mode_get_property¶
Get property metadata.
Definition:
struct drm_mode_get_property {
__u64 values_ptr;
__u64 enum_blob_ptr;
__u32 prop_id;
__u32 flags;
char name[DRM_PROP_NAME_LEN];
__u32 count_values;
__u32 count_enum_blobs;
};
Members
values_ptr
Pointer to a
__u64
array.enum_blob_ptr
Pointer to a
struct drm_mode_property_enum
array.prop_id
Object ID of the property which should be retrieved. Set by the caller.
flags
DRM_MODE_PROP_*
bitfield. Seedrm_property.flags
for a definition of the flags.name
Symbolic property name. User-space should use this field to recognize properties.
count_values
Number of elements in values_ptr.
count_enum_blobs
Number of elements in enum_blob_ptr.
Description
User-space can perform a GETPROPERTY ioctl to retrieve information about a property. The same property may be attached to multiple objects, see “Modeset Base Object Abstraction”.
The meaning of the values_ptr field changes depending on the property type.
See drm_property.flags
for more details.
The enum_blob_ptr and count_enum_blobs fields are only meaningful when the
property has the type DRM_MODE_PROP_ENUM
or DRM_MODE_PROP_BITMASK
. For
backwards compatibility, the kernel will always set count_enum_blobs to
zero when the property has the type DRM_MODE_PROP_BLOB
. User-space must
ignore these two fields if the property has a different type.
User-space is expected to retrieve values and enums by performing this ioctl at least twice: the first time to retrieve the number of elements, the second time to retrieve the elements themselves.
To retrieve the number of elements, set count_values and count_enum_blobs
to zero, then call the ioctl. count_values will be updated with the number
of elements. If the property has the type DRM_MODE_PROP_ENUM
or
DRM_MODE_PROP_BITMASK
, count_enum_blobs will be updated as well.
To retrieve the elements themselves, allocate an array for values_ptr and
set count_values to its capacity. If the property has the type
DRM_MODE_PROP_ENUM
or DRM_MODE_PROP_BITMASK
, allocate an array for
enum_blob_ptr and set count_enum_blobs to its capacity. Calling the ioctl
again will fill the arrays.
-
struct drm_mode_fb_cmd2¶
Frame-buffer metadata.
Definition:
struct drm_mode_fb_cmd2 {
__u32 fb_id;
__u32 width;
__u32 height;
__u32 pixel_format;
__u32 flags;
__u32 handles[4];
__u32 pitches[4];
__u32 offsets[4];
__u64 modifier[4];
};
Members
fb_id
Object ID of the frame-buffer.
width
Width of the frame-buffer.
height
Height of the frame-buffer.
pixel_format
FourCC format code, see
DRM_FORMAT_*
constants indrm_fourcc.h
.flags
Frame-buffer flags (see
DRM_MODE_FB_INTERLACED
andDRM_MODE_FB_MODIFIERS
).handles
GEM buffer handle, one per plane. Set to 0 if the plane is unused. The same handle can be used for multiple planes.
pitches
Pitch (aka. stride) in bytes, one per plane.
offsets
Offset into the buffer in bytes, one per plane.
modifier
Format modifier, one per plane. See
DRM_FORMAT_MOD_*
constants indrm_fourcc.h
. All planes must use the same modifier. Ignored unlessDRM_MODE_FB_MODIFIERS
is set in flags.
Description
This struct holds frame-buffer metadata. There are two ways to use it:
User-space can fill this struct and perform a
DRM_IOCTL_MODE_ADDFB2
ioctl to register a new frame-buffer. The new frame-buffer object ID will be set by the kernel in fb_id.User-space can set fb_id and perform a
DRM_IOCTL_MODE_GETFB2
ioctl to fetch metadata about an existing frame-buffer.
In case of planar formats, this struct allows up to 4 buffer objects with
offsets and pitches per plane. The pitch and offset order are dictated by
the format FourCC as defined by drm_fourcc.h
, e.g. NV12 is described as:
YUV 4:2:0 image with a plane of 8-bit Y samples followed by an interleaved U/V plane containing 8-bit 2x2 subsampled colour difference samples.
So it would consist of a Y plane at offsets[0]
and a UV plane at
offsets[1]
.
To accommodate tiled, compressed, etc formats, a modifier can be specified. For more information see the “Format Modifiers” section. Note that even though it looks like we have a modifier per-plane, we in fact do not. The modifier for each plane must be identical. Thus all combinations of different data layouts for multi-plane formats must be enumerated as separate modifiers.
All of the entries in handles, pitches, offsets and modifier must be
zero when unused. Warning, for offsets and modifier zero can’t be used to
figure out whether the entry is used or not since it’s a valid value (a zero
offset is common, and a zero modifier is DRM_FORMAT_MOD_LINEAR
).
-
struct drm_plane_size_hint¶
Plane size hints
Definition:
struct drm_plane_size_hint {
__u16 width;
__u16 height;
};
Members
width
The width of the plane in pixel
height
The height of the plane in pixel
Description
The plane SIZE_HINTS property blob contains an
array of struct drm_plane_size_hint
.
-
struct hdr_metadata_infoframe¶
HDR Metadata Infoframe Data.
Definition:
struct hdr_metadata_infoframe {
__u8 eotf;
__u8 metadata_type;
struct {
__u16 x, y;
} display_primaries[3];
struct {
__u16 x, y;
} white_point;
__u16 max_display_mastering_luminance;
__u16 min_display_mastering_luminance;
__u16 max_cll;
__u16 max_fall;
};
Members
eotf
Electro-Optical Transfer Function (EOTF) used in the stream.
metadata_type
Static_Metadata_Descriptor_ID.
display_primaries
Color Primaries of the Data. These are coded as unsigned 16-bit values in units of 0.00002, where 0x0000 represents zero and 0xC350 represents 1.0000. display_primaries.x: X coordinate of color primary. display_primaries.y: Y coordinate of color primary.
white_point
White Point of Colorspace Data. These are coded as unsigned 16-bit values in units of 0.00002, where 0x0000 represents zero and 0xC350 represents 1.0000. white_point.x: X coordinate of whitepoint of color primary. white_point.y: Y coordinate of whitepoint of color primary.
max_display_mastering_luminance
Max Mastering Display Luminance. This value is coded as an unsigned 16-bit value in units of 1 cd/m2, where 0x0001 represents 1 cd/m2 and 0xFFFF represents 65535 cd/m2.
min_display_mastering_luminance
Min Mastering Display Luminance. This value is coded as an unsigned 16-bit value in units of 0.0001 cd/m2, where 0x0001 represents 0.0001 cd/m2 and 0xFFFF represents 6.5535 cd/m2.
max_cll
Max Content Light Level. This value is coded as an unsigned 16-bit value in units of 1 cd/m2, where 0x0001 represents 1 cd/m2 and 0xFFFF represents 65535 cd/m2.
max_fall
Max Frame Average Light Level. This value is coded as an unsigned 16-bit value in units of 1 cd/m2, where 0x0001 represents 1 cd/m2 and 0xFFFF represents 65535 cd/m2.
Description
HDR Metadata Infoframe as per CTA 861.G spec. This is expected to match exactly with the spec.
Userspace is expected to pass the metadata information as per the format described in this structure.
-
struct hdr_output_metadata¶
HDR output metadata
Definition:
struct hdr_output_metadata {
__u32 metadata_type;
union {
struct hdr_metadata_infoframe hdmi_metadata_type1;
};
};
Members
metadata_type
Static_Metadata_Descriptor_ID.
{unnamed_union}
anonymous
hdmi_metadata_type1
HDR Metadata Infoframe.
Description
Metadata Information to be passed from userspace
-
DRM_MODE_PAGE_FLIP_EVENT¶
DRM_MODE_PAGE_FLIP_EVENT
Description
Request that the kernel sends back a vblank event (see struct drm_event_vblank) with the
DRM_EVENT_FLIP_COMPLETE
type when the page-flip is done.
-
DRM_MODE_PAGE_FLIP_ASYNC¶
DRM_MODE_PAGE_FLIP_ASYNC
Description
Request that the page-flip is performed as soon as possible, ie. with no delay due to waiting for vblank. This may cause tearing to be visible on the screen.
When used with atomic uAPI, the driver will return an error if the hardware doesn’t support performing an asynchronous page-flip for this update. User-space should handle this, e.g. by falling back to a regular page-flip.
Note, some hardware might need to perform one last synchronous page-flip before being able to switch to asynchronous page-flips. As an exception, the driver will return success even though that first page-flip is not asynchronous.
-
DRM_MODE_PAGE_FLIP_FLAGS¶
DRM_MODE_PAGE_FLIP_FLAGS
Description
Bitmask of flags suitable for
drm_mode_crtc_page_flip_target.flags
.
-
struct drm_mode_create_dumb¶
Create a KMS dumb buffer for scanout.
Definition:
struct drm_mode_create_dumb {
__u32 height;
__u32 width;
__u32 bpp;
__u32 flags;
__u32 handle;
__u32 pitch;
__u64 size;
};
Members
height
buffer height in pixels
width
buffer width in pixels
bpp
bits per pixel
flags
must be zero
handle
buffer object handle
pitch
number of bytes between two consecutive lines
size
size of the whole buffer in bytes
Description
User-space fills height, width, bpp and flags. If the IOCTL succeeds, the kernel fills handle, pitch and size.
-
DRM_MODE_ATOMIC_TEST_ONLY¶
DRM_MODE_ATOMIC_TEST_ONLY
Description
Do not apply the atomic commit, instead check whether the hardware supports this configuration.
See
drm_mode_config_funcs.atomic_check
for more details on test-only commits.
-
DRM_MODE_ATOMIC_NONBLOCK¶
DRM_MODE_ATOMIC_NONBLOCK
Description
Do not block while applying the atomic commit. The
DRM_IOCTL_MODE_ATOMIC
IOCTL returns immediately instead of waiting for the changes to be applied in hardware. Note, the driver will still check that the update can be applied before retuning.
-
DRM_MODE_ATOMIC_ALLOW_MODESET¶
DRM_MODE_ATOMIC_ALLOW_MODESET
Description
Allow the update to result in temporary or transient visible artifacts while the update is being applied. Applying the update may also take significantly more time than a page flip. All visual artifacts will disappear by the time the update is completed, as signalled through the vblank event’s timestamp (see struct drm_event_vblank).
This flag must be set when the KMS update might cause visible artifacts. Without this flag such KMS update will return a EINVAL error. What kind of update may cause visible artifacts depends on the driver and the hardware. User-space that needs to know beforehand if an update might cause visible artifacts can use
DRM_MODE_ATOMIC_TEST_ONLY
withoutDRM_MODE_ATOMIC_ALLOW_MODESET
to see if it fails.To the best of the driver’s knowledge, visual artifacts are guaranteed to not appear when this flag is not set. Some sinks might display visual artifacts outside of the driver’s control.
-
DRM_MODE_ATOMIC_FLAGS¶
DRM_MODE_ATOMIC_FLAGS
Description
Bitfield of flags accepted by the
DRM_IOCTL_MODE_ATOMIC
IOCTL indrm_mode_atomic.flags
.
-
struct drm_mode_create_blob¶
Create New blob property
Definition:
struct drm_mode_create_blob {
__u64 data;
__u32 length;
__u32 blob_id;
};
Members
data
Pointer to data to copy.
length
Length of data to copy.
blob_id
Return: new property ID.
Description
Create a new ‘blob’ data property, copying length bytes from data pointer, and returning new blob ID.
-
struct drm_mode_destroy_blob¶
Destroy user blob
Definition:
struct drm_mode_destroy_blob {
__u32 blob_id;
};
Members
blob_id
blob_id to destroy
Description
Destroy a user-created blob property.
User-space can release blobs as soon as they do not need to refer to them by their blob object ID. For instance, if you are using a MODE_ID blob in an atomic commit and you will not make another commit re-using the same ID, you can destroy the blob as soon as the commit has been issued, without waiting for it to complete.
-
struct drm_mode_create_lease¶
Create lease
Definition:
struct drm_mode_create_lease {
__u64 object_ids;
__u32 object_count;
__u32 flags;
__u32 lessee_id;
__u32 fd;
};
Members
object_ids
Pointer to array of object ids (__u32)
object_count
Number of object ids
flags
flags for new FD (O_CLOEXEC, etc)
lessee_id
Return: unique identifier for lessee.
fd
Return: file descriptor to new drm_master file
Description
Lease mode resources, creating another drm_master.
The object_ids array must reference at least one CRTC, one connector and
one plane if DRM_CLIENT_CAP_UNIVERSAL_PLANES
is enabled. Alternatively,
the lease can be completely empty.
-
struct drm_mode_list_lessees¶
List lessees
Definition:
struct drm_mode_list_lessees {
__u32 count_lessees;
__u32 pad;
__u64 lessees_ptr;
};
Members
count_lessees
Number of lessees.
On input, provides length of the array. On output, provides total number. No more than the input number will be written back, so two calls can be used to get the size and then the data.
pad
Padding.
lessees_ptr
Pointer to lessees.
Pointer to __u64 array of lessee ids
Description
List lesses from a drm_master.
-
struct drm_mode_get_lease¶
Get Lease
Definition:
struct drm_mode_get_lease {
__u32 count_objects;
__u32 pad;
__u64 objects_ptr;
};
Members
count_objects
Number of leased objects.
On input, provides length of the array. On output, provides total number. No more than the input number will be written back, so two calls can be used to get the size and then the data.
pad
Padding.
objects_ptr
Pointer to objects.
Pointer to __u32 array of object ids.
Description
Get leased objects.
-
struct drm_mode_revoke_lease¶
Revoke lease
Definition:
struct drm_mode_revoke_lease {
__u32 lessee_id;
};
Members
lessee_id
Unique ID of lessee
-
struct drm_mode_rect¶
Two dimensional rectangle.
Definition:
struct drm_mode_rect {
__s32 x1;
__s32 y1;
__s32 x2;
__s32 y2;
};
Members
x1
Horizontal starting coordinate (inclusive).
y1
Vertical starting coordinate (inclusive).
x2
Horizontal ending coordinate (exclusive).
y2
Vertical ending coordinate (exclusive).
Description
With drm subsystem using struct drm_rect
to manage rectangular area this
export it to user-space.
Currently used by drm_mode_atomic blob property FB_DAMAGE_CLIPS.
-
struct drm_mode_closefb¶
Definition:
struct drm_mode_closefb {
__u32 fb_id;
__u32 pad;
};
Members
fb_id
Framebuffer ID.
pad
Must be zero.
dma-buf interoperability¶
Please see Exchanging pixel buffers for information on how dma-buf is integrated and exposed within DRM.