FPGA Region¶

Overview¶

This document is meant to be a brief overview of the FPGA region API usage. A more conceptual look at regions can be found in the Device Tree binding document [1].

For the purposes of this API document, let’s just say that a region associates an FPGA Manager and a bridge (or bridges) with a reprogrammable region of an FPGA or the whole FPGA. The API provides a way to register a region and to program a region.

Currently the only layer above fpga-region.c in the kernel is the Device Tree support (of-fpga-region.c) described in [1]. The DT support layer uses regions to program the FPGA and then DT to handle enumeration. The common region code is intended to be used by other schemes that have other ways of accomplishing enumeration after programming.

An fpga-region can be set up to know the following things:

which FPGA manager to use to do the programming

which bridges to disable before programming and enable afterwards.

Additional info needed to program the FPGA image is passed in the struct fpga_image_info including:

pointers to the image as either a scatter-gather buffer, a contiguous buffer, or the name of firmware file

flags indicating specifics such as whether the image is for partial reconfiguration.

How to add a new FPGA region¶

An example of usage can be seen in the probe function of [2].

API to add a new FPGA region¶

struct fpga_region - The FPGA region struct
struct fpga_region_info - Parameter structure for __fpga_region_register_full()
__fpga_region_register_full() - Create and register an FPGA region using the fpga_region_info structure to provide the full flexibility of options
__fpga_region_register() - Create and register an FPGA region using standard arguments
fpga_region_unregister() - Unregister an FPGA region

Helper macros fpga_region_register() and fpga_region_register_full() automatically set the module that registers the FPGA region as the owner.

The FPGA region’s probe function will need to get a reference to the FPGA Manager it will be using to do the programming. This usually would happen during the region’s probe function.

fpga_mgr_get() - Get a reference to an FPGA manager, raise ref count
of_fpga_mgr_get() - Get a reference to an FPGA manager, raise ref count, given a device node.
fpga_mgr_put() - Put an FPGA manager

The FPGA region will need to specify which bridges to control while programming the FPGA. The region driver can build a list of bridges during probe time (fpga_region->bridge_list) or it can have a function that creates the list of bridges to program just before programming (fpga_region->get_bridges). The FPGA bridge framework supplies the following APIs to handle building or tearing down that list.

fpga_bridge_get_to_list() - Get a ref of an FPGA bridge, add it to a list
of_fpga_bridge_get_to_list() - Get a ref of an FPGA bridge, add it to a list, given a device node
fpga_bridges_put() - Given a list of bridges, put them

struct fpga_region¶: FPGA Region structure

Definition:

struct fpga_region {
    struct device dev;
    struct mutex mutex;
    struct list_head bridge_list;
    struct fpga_manager *mgr;
    struct fpga_image_info *info;
    struct fpga_compat_id *compat_id;
    struct module *ops_owner;
    void *priv;
    int (*get_bridges)(struct fpga_region *region);
};

Members

dev: FPGA Region device
mutex: enforces exclusive reference to region
bridge_list: list of FPGA bridges specified in region
mgr: FPGA manager
info: FPGA image info
compat_id: FPGA region id for compatibility check.
ops_owner: module containing the get_bridges function
priv: private data
get_bridges: optional function to get bridges to a list

struct fpga_region_info¶: collection of parameters an FPGA Region

Definition:

struct fpga_region_info {
    struct fpga_manager *mgr;
    struct fpga_compat_id *compat_id;
    void *priv;
    int (*get_bridges)(struct fpga_region *region);
};

Members

mgr: fpga region manager
compat_id: FPGA region id for compatibility check.
priv: fpga region private data
get_bridges: optional function to get bridges to a list

Description

fpga_region_info contains parameters for the register_full function. These are separated into an info structure because they some are optional others could be added to in the future. The info structure facilitates maintaining a stable API.

struct fpga_region *__fpga_region_register_full(struct device *parent, const struct fpga_region_info *info, struct module *owner)¶: create and register an FPGA Region device

Parameters

struct device *parent: device parent
const struct fpga_region_info *info: parameters for FPGA Region
struct module *owner: module containing the get_bridges function

Return

struct fpga_region or ERR_PTR()

struct fpga_region *__fpga_region_register(struct device *parent, struct fpga_manager *mgr, int (*get_bridges)(struct fpga_region*), struct module *owner)¶: create and register an FPGA Region device

Parameters

struct device *parent: device parent
struct fpga_manager *mgr: manager that programs this region
int (*get_bridges)(struct fpga_region *): optional function to get bridges to a list
struct module *owner: module containing the get_bridges function

Description

This simple version of the register function should be sufficient for most users. The fpga_region_register_full() function is available for users that need to pass additional, optional parameters.

Return

struct fpga_region or ERR_PTR()

void fpga_region_unregister(struct fpga_region *region)¶: unregister an FPGA region

Parameters

struct fpga_region *region: FPGA region

Description

This function is intended for use in an FPGA region driver’s remove function.

struct fpga_manager *fpga_mgr_get(struct device *dev)¶: Given a device, get a reference to an fpga mgr.

Parameters

struct device *dev: parent device that fpga mgr was registered with

Return

fpga manager struct or IS_ERR() condition containing error code.

struct fpga_manager *of_fpga_mgr_get(struct device_node *node)¶: Given a device node, get a reference to an fpga mgr.

Parameters

struct device_node *node: device node

Return

fpga manager struct or IS_ERR() condition containing error code.

void fpga_mgr_put(struct fpga_manager *mgr)¶: release a reference to an fpga manager

Parameters

struct fpga_manager *mgr: fpga manager structure

int fpga_bridge_get_to_list(struct device *dev, struct fpga_image_info *info, struct list_head *bridge_list)¶: given device, get a bridge, add it to a list

Parameters

struct device *dev: FPGA bridge device
struct fpga_image_info *info: fpga image specific information
struct list_head *bridge_list: list of FPGA bridges

Description

Get an exclusive reference to the bridge and it to the list.

Return

0 for success, error code from fpga_bridge_get() otherwise.

int of_fpga_bridge_get_to_list(struct device_node *np, struct fpga_image_info *info, struct list_head *bridge_list)¶: get a bridge, add it to a list

Parameters

struct device_node *np: node pointer of an FPGA bridge
struct fpga_image_info *info: fpga image specific information
struct list_head *bridge_list: list of FPGA bridges

Description

Get an exclusive reference to the bridge and it to the list.

Return

0 for success, error code from of_fpga_bridge_get() otherwise.

void fpga_bridges_put(struct list_head *bridge_list)¶: put bridges

Parameters

struct list_head *bridge_list: list of FPGA bridges

Description

For each bridge in the list, put the bridge and remove it from the list. If list is empty, do nothing.