Parallel Port Devices¶

parport_register_driver¶

parport_register_driver (driver)

register a parallel port device driver

Parameters

driver

structure describing the driver

This can be called by a parallel port device driver in order to receive notifications about ports being found in the system, as well as ports no longer available.

The driver structure is allocated by the caller and must not be deallocated until after calling parport_unregister_driver().

If using the non device model: The driver’s attach() function may block. The port that attach() is given will be valid for the duration of the callback, but if the driver wants to take a copy of the pointer it must call parport_get_port() to do so. Calling parport_register_device() on that port will do this for you.

The driver’s detach() function may block. The port that detach() is given will be valid for the duration of the callback, but if the driver wants to take a copy of the pointer it must call parport_get_port() to do so.

Returns 0 on success. The non device model will always succeeds. but the new device model can fail and will return the error code.

module_parport_driver¶

module_parport_driver (__parport_driver)

Helper macro for registering a modular parport driver

Parameters

__parport_driver: struct parport_driver to be used

Description

Helper macro for parport drivers which do not do anything special in module init and exit. This eliminates a lot of boilerplate. Each module may only use this macro once, and calling it replaces module_init() and module_exit().

int parport_yield(struct pardevice *dev)¶: relinquish a parallel port temporarily

Parameters

struct pardevice *dev: a device on the parallel port

Description

This function relinquishes the port if it would be helpful to other drivers to do so. Afterwards it tries to reclaim the port using parport_claim(), and the return value is the same as for parport_claim(). If it fails, the port is left unclaimed and it is the driver’s responsibility to reclaim the port.

The parport_yield() and parport_yield_blocking() functions are for marking points in the driver at which other drivers may claim the port and use their devices. Yielding the port is similar to releasing it and reclaiming it, but is more efficient because no action is taken if there are no other devices needing the port. In fact, nothing is done even if there are other devices waiting but the current device is still within its “timeslice”. The default timeslice is half a second, but it can be adjusted via the /proc interface.

int parport_yield_blocking(struct pardevice *dev)¶: relinquish a parallel port temporarily

Parameters

struct pardevice *dev: a device on the parallel port

Description

This function relinquishes the port if it would be helpful to other drivers to do so. Afterwards it tries to reclaim the port using parport_claim_or_block(), and the return value is the same as for parport_claim_or_block().

int parport_wait_event(struct parport *port, signed long timeout)¶: wait for an event on a parallel port

Parameters

struct parport *port

port to wait on

signed long timeout

time to wait (in jiffies)

This function waits for up to timeout jiffies for an interrupt to occur on a parallel port. If the port timeout is set to zero, it returns immediately.

If an interrupt occurs before the timeout period elapses, this function returns zero immediately. If it times out, it returns one. An error code less than zero indicates an error (most likely a pending signal), and the calling code should finish what it’s doing as soon as it can.

int parport_wait_peripheral(struct parport *port, unsigned char mask, unsigned char result)¶: wait for status lines to change in 35ms

Parameters

struct parport *port

port to watch

unsigned char mask

status lines to watch

unsigned char result

desired values of chosen status lines

This function waits until the masked status lines have the desired values, or until 35ms have elapsed (see IEEE 1284-1994 page 24 to 25 for why this value in particular is hardcoded). The mask and result parameters are bitmasks, with the bits defined by the constants in parport.h: PARPORT_STATUS_BUSY, and so on.

The port is polled quickly to start off with, in anticipation of a fast response from the peripheral. This fast polling time is configurable (using /proc), and defaults to 500usec. If the timeout for this port (see parport_set_timeout()) is zero, the fast polling time is 35ms, and this function does not call schedule().

If the timeout for this port is non-zero, after the fast polling fails it uses parport_wait_event() to wait for up to 10ms, waking up if an interrupt occurs.

int parport_negotiate(struct parport *port, int mode)¶: negotiate an IEEE 1284 mode

Parameters

struct parport *port

port to use

int mode

mode to negotiate to

Use this to negotiate to a particular IEEE 1284 transfer mode. The mode parameter should be one of the constants in parport.h starting IEEE1284_MODE_xxx.

The return value is 0 if the peripheral has accepted the negotiation to the mode specified, -1 if the peripheral is not IEEE 1284 compliant (or not present), or 1 if the peripheral has rejected the negotiation.

ssize_t parport_write(struct parport *port, const void *buffer, size_t len)¶: write a block of data to a parallel port

Parameters

struct parport *port

port to write to

const void *buffer

data buffer (in kernel space)

size_t len

number of bytes of data to transfer

This will write up to len bytes of buffer to the port specified, using the IEEE 1284 transfer mode most recently negotiated to (using parport_negotiate()), as long as that mode supports forward transfers (host to peripheral).

It is the caller’s responsibility to ensure that the first len bytes of buffer are valid.

This function returns the number of bytes transferred (if zero or positive), or else an error code.

ssize_t parport_read(struct parport *port, void *buffer, size_t len)¶: read a block of data from a parallel port

Parameters

struct parport *port

port to read from

void *buffer

data buffer (in kernel space)

size_t len

number of bytes of data to transfer

This will read up to len bytes of buffer to the port specified, using the IEEE 1284 transfer mode most recently negotiated to (using parport_negotiate()), as long as that mode supports reverse transfers (peripheral to host).

It is the caller’s responsibility to ensure that the first len bytes of buffer are available to write to.

This function returns the number of bytes transferred (if zero or positive), or else an error code.

long parport_set_timeout(struct pardevice *dev, long inactivity)¶: set the inactivity timeout for a device

Parameters

struct pardevice *dev

device on a port

long inactivity

inactivity timeout (in jiffies)

This sets the inactivity timeout for a particular device on a port. This affects functions like parport_wait_peripheral(). The special value 0 means not to call schedule() while dealing with this device.

The return value is the previous inactivity timeout.

Any callers of parport_wait_event() for this device are woken up.

int __parport_register_driver(struct parport_driver *drv, struct module *owner, const char *mod_name)¶: register a parallel port device driver

Parameters

struct parport_driver *drv

structure describing the driver

struct module *owner

owner module of drv

const char *mod_name

module name string

This can be called by a parallel port device driver in order to receive notifications about ports being found in the system, as well as ports no longer available.

If devmodel is true then the new device model is used for registration.

The drv structure is allocated by the caller and must not be deallocated until after calling parport_unregister_driver().

If using the non device model: The driver’s attach() function may block. The port that attach() is given will be valid for the duration of the callback, but if the driver wants to take a copy of the pointer it must call parport_get_port() to do so. Calling parport_register_device() on that port will do this for you.

The driver’s detach() function may block. The port that detach() is given will be valid for the duration of the callback, but if the driver wants to take a copy of the pointer it must call parport_get_port() to do so.

Returns 0 on success. The non device model will always succeeds. but the new device model can fail and will return the error code.

void parport_unregister_driver(struct parport_driver *drv)¶: deregister a parallel port device driver

Parameters

struct parport_driver *drv: structure describing the driver that was given to parport_register_driver()

This should be called by a parallel port device driver that has registered itself using parport_register_driver() when it is about to be unloaded.

When it returns, the driver’s attach() routine will no longer be called, and for each port that attach() was called for, the detach() routine will have been called.

All the driver’s attach() and detach() calls are guaranteed to have finished by the time this function returns.

struct parport *parport_get_port(struct parport *port)¶: increment a port’s reference count

Parameters

struct parport *port

the port

This ensures that a struct parport pointer remains valid until the matching parport_put_port() call.

void parport_put_port(struct parport *port)¶: decrement a port’s reference count

Parameters

struct parport *port

the port

This should be called once for each call to parport_get_port(), once the port is no longer needed. When the reference count reaches zero (port is no longer used), free_port is called.

struct parport *parport_register_port(unsigned long base, int irq, int dma, struct parport_operations *ops)¶: register a parallel port

Parameters

unsigned long base

base I/O address

int irq

IRQ line

int dma

DMA channel

struct parport_operations *ops

pointer to the port driver’s port operations structure

When a parallel port (lowlevel) driver finds a port that should be made available to parallel port device drivers, it should call parport_register_port(). The base, irq, and dma parameters are for the convenience of port drivers, and for ports where they aren’t meaningful needn’t be set to anything special. They can be altered afterwards by adjusting the relevant members of the parport structure that is returned and represents the port. They should not be tampered with after calling parport_announce_port, however.

If there are parallel port device drivers in the system that have registered themselves using parport_register_driver(), they are not told about the port at this time; that is done by parport_announce_port().

The ops structure is allocated by the caller, and must not be deallocated before calling parport_remove_port().

If there is no memory to allocate a new parport structure, this function will return NULL.

void parport_announce_port(struct parport *port)¶: tell device drivers about a parallel port

Parameters

struct parport *port

parallel port to announce

After a port driver has registered a parallel port with parport_register_port, and performed any necessary initialisation or adjustments, it should call parport_announce_port() in order to notify all device drivers that have called parport_register_driver(). Their attach() functions will be called, with port as the parameter.

void parport_remove_port(struct parport *port)¶: deregister a parallel port

Parameters

struct parport *port

parallel port to deregister

When a parallel port driver is forcibly unloaded, or a parallel port becomes inaccessible, the port driver must call this function in order to deal with device drivers that still want to use it.

The parport structure associated with the port has its operations structure replaced with one containing ‘null’ operations that return errors or just don’t do anything.

Any drivers that have registered themselves using parport_register_driver() are notified that the port is no longer accessible by having their detach() routines called with port as the parameter.

struct pardevice *parport_register_dev_model(struct parport *port, const char *name, const struct pardev_cb *par_dev_cb, int id)¶: register a device on a parallel port

Parameters

struct parport *port

port to which the device is attached

const char *name

a name to refer to the device

const struct pardev_cb *par_dev_cb

struct containing callbacks

int id

device number to be given to the device

This function, called by parallel port device drivers, declares that a device is connected to a port, and tells the system all it needs to know.

The struct pardev_cb contains pointer to callbacks. preemption callback function, preempt, is called when this device driver has claimed access to the port but another device driver wants to use it. It is given, private, as its parameter, and should return zero if it is willing for the system to release the port to another driver on its behalf. If it wants to keep control of the port it should return non-zero, and no action will be taken. It is good manners for the driver to try to release the port at the earliest opportunity after its preemption callback rejects a preemption attempt. Note that if a preemption callback is happy for preemption to go ahead, there is no need to release the port; it is done automatically. This function may not block, as it may be called from interrupt context. If the device driver does not support preemption, preempt can be NULL.

The wake-up (“kick”) callback function, wakeup, is called when the port is available to be claimed for exclusive access; that is, parport_claim() is guaranteed to succeed when called from inside the wake-up callback function. If the driver wants to claim the port it should do so; otherwise, it need not take any action. This function may not block, as it may be called from interrupt context. If the device driver does not want to be explicitly invited to claim the port in this way, wakeup can be NULL.

The interrupt handler, irq_func, is called when an interrupt arrives from the parallel port. Note that if a device driver wants to use interrupts it should use parport_enable_irq(), and can also check the irq member of the parport structure representing the port.

The parallel port (lowlevel) driver is the one that has called request_irq() and whose interrupt handler is called first. This handler does whatever needs to be done to the hardware to acknowledge the interrupt (for PC-style ports there is nothing special to be done). It then tells the IEEE 1284 code about the interrupt, which may involve reacting to an IEEE 1284 event depending on the current IEEE 1284 phase. After this, it calls irq_func. Needless to say, irq_func will be called from interrupt context, and may not block.

The PARPORT_DEV_EXCL flag is for preventing port sharing, and so should only be used when sharing the port with other device drivers is impossible and would lead to incorrect behaviour. Use it sparingly! Normally, flags will be zero.

This function returns a pointer to a structure that represents the device on the port, or NULL if there is not enough memory to allocate space for that structure.

void parport_unregister_device(struct pardevice *dev)¶: deregister a device on a parallel port

Parameters

struct pardevice *dev

pointer to structure representing device

This undoes the effect of parport_register_device().

struct parport *parport_find_number(int number)¶: find a parallel port by number

Parameters

int number

parallel port number

This returns the parallel port with the specified number, or NULL if there is none.

There is an implicit parport_get_port() done already; to throw away the reference to the port that parport_find_number() gives you, use parport_put_port().

struct parport *parport_find_base(unsigned long base)¶: find a parallel port by base address

Parameters

unsigned long base

base I/O address

This returns the parallel port with the specified base address, or NULL if there is none.

There is an implicit parport_get_port() done already; to throw away the reference to the port that parport_find_base() gives you, use parport_put_port().

int parport_claim(struct pardevice *dev)¶: claim access to a parallel port device

Parameters

struct pardevice *dev

pointer to structure representing a device on the port

This function will not block and so can be used from interrupt context. If parport_claim() succeeds in claiming access to the port it returns zero and the port is available to use. It may fail (returning non-zero) if the port is in use by another driver and that driver is not willing to relinquish control of the port.

int parport_claim_or_block(struct pardevice *dev)¶: claim access to a parallel port device

Parameters

struct pardevice *dev

pointer to structure representing a device on the port

This behaves like parport_claim(), but will block if necessary to wait for the port to be free. A return value of 1 indicates that it slept; 0 means that it succeeded without needing to sleep. A negative error code indicates failure.

void parport_release(struct pardevice *dev)¶: give up access to a parallel port device

Parameters

struct pardevice *dev

pointer to structure representing parallel port device

This function cannot fail, but it should not be called without the port claimed. Similarly, if the port is already claimed you should not try claiming it again.

struct pardevice *parport_open(int devnum, const char *name)¶: find a device by canonical device number

Parameters

int devnum

canonical device number

const char *name

name to associate with the device

This function is similar to parport_register_device(), except that it locates a device by its number rather than by the port it is attached to.

All parameters except for devnum are the same as for parport_register_device(). The return value is the same as for parport_register_device().

void parport_close(struct pardevice *dev)¶: close a device opened with parport_open()

Parameters

struct pardevice *dev

device to close

This is to parport_open() as parport_unregister_device() is to parport_register_device().

16x50 UART Driver¶

struct uart_8250_port *serial8250_get_port(int line)¶: retrieve struct uart_8250_port

Parameters

int line: serial line number

Description

This function retrieves struct uart_8250_port for the specific line. This struct must not be used to perform a 8250 or serial core operation which is not accessible otherwise. Its only purpose is to make the struct accessible to the runtime-pm callbacks for context suspend/restore. The lock assumption made here is none because runtime-pm suspend/resume callbacks should not be invoked if there is any operation performed on the port.

void serial8250_suspend_port(int line)¶: suspend one serial port

Parameters

int line

serial line number

Suspend one serial port.

void serial8250_resume_port(int line)¶: resume one serial port

Parameters

int line

serial line number

Resume one serial port.

int serial8250_register_8250_port(const struct uart_8250_port *up)¶: register a serial port

Parameters

const struct uart_8250_port *up

serial port template

Configure the serial port specified by the request. If the port exists and is in use, it is hung up and unregistered first.

The port is then probed and if necessary the IRQ is autodetected If this fails an error is returned.

On success the port is ready to use and the line number is returned.

void serial8250_unregister_port(int line)¶: remove a 16x50 serial port at runtime

Parameters

int line

serial line number

Remove one serial port. This may not be called from interrupt context. We hand the port back to the our control.

See Low Level Serial API for related APIs.

Pulse-Width Modulation (PWM)¶

Pulse-width modulation is a modulation technique primarily used to control power supplied to electrical devices.

The PWM framework provides an abstraction for providers and consumers of PWM signals. A controller that provides one or more PWM signals is registered as struct pwm_chip. Providers are expected to embed this structure in a driver-specific structure. This structure contains fields that describe a particular chip.

A chip exposes one or more PWM signal sources, each of which exposed as a struct pwm_device. Operations can be performed on PWM devices to control the period, duty cycle, polarity and active state of the signal.

Note that PWM devices are exclusive resources: they can always only be used by one consumer at a time.

enum pwm_polarity¶: polarity of a PWM signal

Constants

PWM_POLARITY_NORMAL: a high signal for the duration of the duty- cycle, followed by a low signal for the remainder of the pulse period
PWM_POLARITY_INVERSED: a low signal for the duration of the duty- cycle, followed by a high signal for the remainder of the pulse period

struct pwm_args¶: board-dependent PWM arguments

Definition:

struct pwm_args {
    u64 period;
    enum pwm_polarity polarity;
};

Members

period: reference period
polarity: reference polarity

Description

This structure describes board-dependent arguments attached to a PWM device. These arguments are usually retrieved from the PWM lookup table or device tree.

Do not confuse this with the PWM state: PWM arguments represent the initial configuration that users want to use on this PWM device rather than the current PWM hardware state.

struct pwm_waveform¶: description of a PWM waveform

Definition:

struct pwm_waveform {
    u64 period_length_ns;
    u64 duty_length_ns;
    u64 duty_offset_ns;
};

Members

period_length_ns: PWM period
duty_length_ns: PWM duty cycle
duty_offset_ns: offset of the rising edge from the period’s start

Description

This is a representation of a PWM waveform alternative to struct pwm_state below. It’s more expressive than struct pwm_state as it contains a duty_offset_ns and so can represent offsets other than zero (with .polarity = PWM_POLARITY_NORMAL) and period - duty_cycle (.polarity = PWM_POLARITY_INVERSED).

Note there is no explicit bool for enabled. A “disabled” PWM is represented by .period_length_ns = 0. Note further that the behaviour of a “disabled” PWM is undefined. Depending on the hardware’s capabilities it might drive the active or inactive level, go high-z or even continue to toggle.

The unit for all three members is nanoseconds.

struct pwm_device¶: PWM channel object

Definition:

struct pwm_device {
    const char *label;
    unsigned long flags;
    unsigned int hwpwm;
    struct pwm_chip *chip;
    struct pwm_args args;
    struct pwm_state state;
    struct pwm_state last;
};

Members

label: name of the PWM device
flags: flags associated with the PWM device
hwpwm: per-chip relative index of the PWM device
chip: PWM chip providing this PWM device
args: PWM arguments
state: last applied state
last: last implemented state (for PWM_DEBUG)

void pwm_get_state(const struct pwm_device *pwm, struct pwm_state *state)¶: retrieve the current PWM state

Parameters

const struct pwm_device *pwm: PWM device
struct pwm_state *state: state to fill with the current PWM state

Description

The returned PWM state represents the state that was applied by a previous call to pwm_apply_might_sleep(). Drivers may have to slightly tweak that state before programming it to hardware. If pwm_apply_might_sleep() was never called, this returns either the current hardware state (if supported) or the default settings.

void pwm_init_state(const struct pwm_device *pwm, struct pwm_state *state)¶: prepare a new state to be applied with pwm_apply_might_sleep()

Parameters

const struct pwm_device *pwm: PWM device
struct pwm_state *state: state to fill with the prepared PWM state

Description

This functions prepares a state that can later be tweaked and applied to the PWM device with pwm_apply_might_sleep(). This is a convenient function that first retrieves the current PWM state and the replaces the period and polarity fields with the reference values defined in pwm->args. Once the function returns, you can adjust the ->enabled and ->duty_cycle fields according to your needs before calling pwm_apply_might_sleep().

->duty_cycle is initially set to zero to avoid cases where the current ->duty_cycle value exceed the pwm_args->period one, which would trigger an error if the user calls pwm_apply_might_sleep() without adjusting ->duty_cycle first.

unsigned int pwm_get_relative_duty_cycle(const struct pwm_state *state, unsigned int scale)¶: Get a relative duty cycle value

Parameters

const struct pwm_state *state: PWM state to extract the duty cycle from
unsigned int scale: target scale of the relative duty cycle

Description

This functions converts the absolute duty cycle stored in state (expressed in nanosecond) into a value relative to the period.

For example if you want to get the duty_cycle expressed in percent, call:

pwm_get_state(pwm, state); duty = pwm_get_relative_duty_cycle(state, 100);

int pwm_set_relative_duty_cycle(struct pwm_state *state, unsigned int duty_cycle, unsigned int scale)¶: Set a relative duty cycle value

Parameters

struct pwm_state *state: PWM state to fill
unsigned int duty_cycle: relative duty cycle value
unsigned int scale: scale in which duty_cycle is expressed

Description

This functions converts a relative into an absolute duty cycle (expressed in nanoseconds), and puts the result in state->duty_cycle.

For example if you want to configure a 50% duty cycle, call:

pwm_init_state(pwm, state); pwm_set_relative_duty_cycle(state, 50, 100); pwm_apply_might_sleep(pwm, state);

This functions returns -EINVAL if duty_cycle and/or scale are inconsistent (scale == 0 or duty_cycle > scale).

struct pwm_capture¶: PWM capture data

Definition:

struct pwm_capture {
    unsigned int period;
    unsigned int duty_cycle;
};

Members

period: period of the PWM signal (in nanoseconds)
duty_cycle: duty cycle of the PWM signal (in nanoseconds)

struct pwm_ops¶: PWM controller operations

Definition:

struct pwm_ops {
    int (*request)(struct pwm_chip *chip, struct pwm_device *pwm);
    void (*free)(struct pwm_chip *chip, struct pwm_device *pwm);
    int (*capture)(struct pwm_chip *chip, struct pwm_device *pwm, struct pwm_capture *result, unsigned long timeout);
    size_t sizeof_wfhw;
    int (*round_waveform_tohw)(struct pwm_chip *chip, struct pwm_device *pwm, const struct pwm_waveform *wf, void *wfhw);
    int (*round_waveform_fromhw)(struct pwm_chip *chip, struct pwm_device *pwm, const void *wfhw, struct pwm_waveform *wf);
    int (*read_waveform)(struct pwm_chip *chip, struct pwm_device *pwm, void *wfhw);
    int (*write_waveform)(struct pwm_chip *chip, struct pwm_device *pwm, const void *wfhw);
    int (*apply)(struct pwm_chip *chip, struct pwm_device *pwm, const struct pwm_state *state);
    int (*get_state)(struct pwm_chip *chip, struct pwm_device *pwm, struct pwm_state *state);
};

Members

request: optional hook for requesting a PWM
free: optional hook for freeing a PWM
capture: capture and report PWM signal
sizeof_wfhw: size (in bytes) of driver specific waveform presentation
round_waveform_tohw: convert a struct pwm_waveform to driver specific presentation
round_waveform_fromhw: convert a driver specific waveform presentation to struct pwm_waveform
read_waveform: read driver specific waveform presentation from hardware
write_waveform: write driver specific waveform presentation to hardware
apply: atomically apply a new PWM config
get_state: get the current PWM state.

struct pwm_chip¶: abstract a PWM controller

Definition:

struct pwm_chip {
    struct device dev;
    const struct pwm_ops *ops;
    struct module *owner;
    unsigned int id;
    unsigned int npwm;
    struct pwm_device * (*of_xlate)(struct pwm_chip *chip, const struct of_phandle_args *args);
    bool atomic;
    bool uses_pwmchip_alloc;
    bool operational;
    union {
        struct mutex nonatomic_lock;
        spinlock_t atomic_lock;
    };
    struct pwm_device pwms[] ;
};

Members

dev: device providing the PWMs
ops: callbacks for this PWM controller
owner: module providing this chip
id: unique number of this PWM chip
npwm: number of PWMs controlled by this chip
of_xlate: request a PWM device given a device tree PWM specifier
atomic: can the driver’s ->apply() be called in atomic context
uses_pwmchip_alloc: signals if pwmchip_allow was used to allocate this chip
operational: signals if the chip can be used (or is already deregistered)
{unnamed_union}: anonymous
nonatomic_lock: mutex for nonatomic chips
atomic_lock: mutex for atomic chips
pwms: array of PWM devices allocated by the framework

int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)¶: change a PWM device configuration

Parameters

struct pwm_device *pwm: PWM device
int duty_ns: “on” time (in nanoseconds)
int period_ns: duration (in nanoseconds) of one cycle

Return

0 on success or a negative error code on failure.

int pwm_enable(struct pwm_device *pwm)¶: start a PWM output toggling

Parameters

struct pwm_device *pwm: PWM device

Return

0 on success or a negative error code on failure.

void pwm_disable(struct pwm_device *pwm)¶: stop a PWM output toggling

Parameters

struct pwm_device *pwm: PWM device

bool pwm_might_sleep(struct pwm_device *pwm)¶: is pwm_apply_atomic() supported?

Parameters

struct pwm_device *pwm: PWM device

Return

false if pwm_apply_atomic() can be called from atomic context.

int pwm_round_waveform_might_sleep(struct pwm_device *pwm, struct pwm_waveform *wf)¶: Query hardware capabilities Cannot be used in atomic context.

Parameters

struct pwm_device *pwm: PWM device
struct pwm_waveform *wf: waveform to round and output parameter

Description

Typically a given waveform cannot be implemented exactly by hardware, e.g. because hardware only supports coarse period resolution or no duty_offset. This function returns the actually implemented waveform if you pass wf to pwm_set_waveform_might_sleep now.

Note however that the world doesn’t stop turning when you call it, so when doing

pwm_round_waveform_might_sleep(mypwm, wf); pwm_set_waveform_might_sleep(mypwm, wf, true);

the latter might fail, e.g. because an input clock changed its rate between these two calls and the waveform determined by pwm_round_waveform_might_sleep() cannot be implemented any more.

Returns 0 on success, 1 if there is no valid hardware configuration matching the input waveform under the PWM rounding rules or a negative errno.

int pwm_get_waveform_might_sleep(struct pwm_device *pwm, struct pwm_waveform *wf)¶: Query hardware about current configuration Cannot be used in atomic context.

Parameters

struct pwm_device *pwm: PWM device
struct pwm_waveform *wf: output parameter

Description

Stores the current configuration of the PWM in wf. Note this is the equivalent of pwm_get_state_hw() (and not pwm_get_state()) for pwm_waveform.

int pwm_set_waveform_might_sleep(struct pwm_device *pwm, const struct pwm_waveform *wf, bool exact)¶: Apply a new waveform Cannot be used in atomic context.

Parameters

struct pwm_device *pwm: PWM device
const struct pwm_waveform *wf: The waveform to apply
bool exact: If true no rounding is allowed

Description

Typically a requested waveform cannot be implemented exactly, e.g. because you requested .period_length_ns = 100 ns, but the hardware can only set periods that are a multiple of 8.5 ns. With that hardware passing exact = true results in pwm_set_waveform_might_sleep() failing and returning 1. If exact = false you get a period of 93.5 ns (i.e. the biggest period not bigger than the requested value). Note that even with exact = true, some rounding by less than 1 is possible/needed. In the above example requesting .period_length_ns = 94 and exact = true, you get the hardware configured with period = 93.5 ns.

int pwm_apply_might_sleep(struct pwm_device *pwm, const struct pwm_state *state)¶: atomically apply a new state to a PWM device Cannot be used in atomic context.

Parameters

struct pwm_device *pwm: PWM device
const struct pwm_state *state: new state to apply

int pwm_apply_atomic(struct pwm_device *pwm, const struct pwm_state *state)¶: apply a new state to a PWM device from atomic context Not all PWM devices support this function, check with pwm_might_sleep().

Parameters

struct pwm_device *pwm: PWM device
const struct pwm_state *state: new state to apply

int pwm_get_state_hw(struct pwm_device *pwm, struct pwm_state *state)¶: get the current PWM state from hardware

Parameters

struct pwm_device *pwm: PWM device
struct pwm_state *state: state to fill with the current PWM state

Description

Similar to pwm_get_state() but reads the current PWM state from hardware instead of the requested state.

Return

0 on success or a negative error code on failure.

Context

May sleep.

int pwm_adjust_config(struct pwm_device *pwm)¶: adjust the current PWM config to the PWM arguments

Parameters

struct pwm_device *pwm: PWM device

Description

This function will adjust the PWM config to the PWM arguments provided by the DT or PWM lookup table. This is particularly useful to adapt the bootloader config to the Linux one.

struct pwm_device *pwm_get(struct device *dev, const char *con_id)¶: look up and request a PWM device

Parameters

struct device *dev: device for PWM consumer
const char *con_id: consumer name

Description

Lookup is first attempted using DT. If the device was not instantiated from a device tree, a PWM chip and a relative index is looked up via a table supplied by board setup code (see pwm_add_table()).

Once a PWM chip has been found the specified PWM device will be requested and is ready to be used.

Return

A pointer to the requested PWM device or an ERR_PTR()-encoded error code on failure.

void pwm_put(struct pwm_device *pwm)¶: release a PWM device

Parameters

struct pwm_device *pwm: PWM device

struct pwm_device *devm_pwm_get(struct device *dev, const char *con_id)¶: resource managed pwm_get()

Parameters

struct device *dev: device for PWM consumer
const char *con_id: consumer name

Description

This function performs like pwm_get() but the acquired PWM device will automatically be released on driver detach.

Return

A pointer to the requested PWM device or an ERR_PTR()-encoded error code on failure.

struct pwm_device *devm_fwnode_pwm_get(struct device *dev, struct fwnode_handle *fwnode, const char *con_id)¶: request a resource managed PWM from firmware node

Parameters

struct device *dev: device for PWM consumer
struct fwnode_handle *fwnode: firmware node to get the PWM from
const char *con_id: consumer name

Description

Returns the PWM device parsed from the firmware node. See of_pwm_get() and acpi_pwm_get() for a detailed description.

Return

A pointer to the requested PWM device or an ERR_PTR()-encoded error code on failure.

int __pwmchip_add(struct pwm_chip *chip, struct module *owner)¶: register a new PWM chip

Parameters

struct pwm_chip *chip: the PWM chip to add
struct module *owner: reference to the module providing the chip.

Description

Register a new PWM chip. owner is supposed to be THIS_MODULE, use the pwmchip_add wrapper to do this right.

Return

0 on success or a negative error code on failure.

void pwmchip_remove(struct pwm_chip *chip)¶: remove a PWM chip

Parameters

struct pwm_chip *chip: the PWM chip to remove

Description

Removes a PWM chip.