Parallel Port Devices¶
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parport_register_driver¶
parport_register_driver (driver)
register a parallel port device driver
Parameters
driverstructure 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.
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module_parport_driver¶
module_parport_driver (__parport_driver)
Helper macro for registering a modular parport driver
Parameters
__parport_driverstruct 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().
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int parport_yield(struct pardevice *dev)¶
relinquish a parallel port temporarily
Parameters
struct pardevice *deva 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.
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int parport_yield_blocking(struct pardevice *dev)¶
relinquish a parallel port temporarily
Parameters
struct pardevice *deva 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().
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int parport_wait_event(struct parport *port, signed long timeout)¶
wait for an event on a parallel port
Parameters
struct parport *portport to wait on
signed long timeouttime 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.
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int parport_wait_peripheral(struct parport *port, unsigned char mask, unsigned char result)¶
wait for status lines to change in 35ms
Parameters
struct parport *portport to watch
unsigned char maskstatus lines to watch
unsigned char resultdesired 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.
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int parport_negotiate(struct parport *port, int mode)¶
negotiate an IEEE 1284 mode
Parameters
struct parport *portport to use
int modemode 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.
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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 *portport to write to
const void *bufferdata buffer (in kernel space)
size_t lennumber 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.
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ssize_t parport_read(struct parport *port, void *buffer, size_t len)¶
read a block of data from a parallel port
Parameters
struct parport *portport to read from
void *bufferdata buffer (in kernel space)
size_t lennumber 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.
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long parport_set_timeout(struct pardevice *dev, long inactivity)¶
set the inactivity timeout for a device
Parameters
struct pardevice *devdevice on a port
long inactivityinactivity 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.
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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 *drvstructure describing the driver
struct module *ownerowner module of drv
const char *mod_namemodule 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.
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void parport_unregister_driver(struct parport_driver *drv)¶
deregister a parallel port device driver
Parameters
struct parport_driver *drvstructure 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.
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struct parport *parport_get_port(struct parport *port)¶
increment a port’s reference count
Parameters
struct parport *portthe port
This ensures that a struct parport pointer remains valid until the matching
parport_put_port()call.
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void parport_put_port(struct parport *port)¶
decrement a port’s reference count
Parameters
struct parport *portthe 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.
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struct parport *parport_register_port(unsigned long base, int irq, int dma, struct parport_operations *ops)¶
register a parallel port
Parameters
unsigned long basebase I/O address
int irqIRQ line
int dmaDMA channel
struct parport_operations *opspointer 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 byparport_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.
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void parport_announce_port(struct parport *port)¶
tell device drivers about a parallel port
Parameters
struct parport *portparallel 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 calledparport_register_driver(). Their attach() functions will be called, with port as the parameter.
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void parport_remove_port(struct parport *port)¶
deregister a parallel port
Parameters
struct parport *portparallel 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.
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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 *portport to which the device is attached
const char *namea name to refer to the device
const struct pardev_cb *par_dev_cbstruct containing callbacks
int iddevice 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 beNULL.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_EXCLflag 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
NULLif there is not enough memory to allocate space for that structure.
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void parport_unregister_device(struct pardevice *dev)¶
deregister a device on a parallel port
Parameters
struct pardevice *devpointer to structure representing device
This undoes the effect of parport_register_device().
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struct parport *parport_find_number(int number)¶
find a parallel port by number
Parameters
int numberparallel port number
This returns the parallel port with the specified number, or
NULLif there is none.There is an implicit
parport_get_port()done already; to throw away the reference to the port thatparport_find_number()gives you, useparport_put_port().
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struct parport *parport_find_base(unsigned long base)¶
find a parallel port by base address
Parameters
unsigned long basebase I/O address
This returns the parallel port with the specified base address, or
NULLif there is none.There is an implicit
parport_get_port()done already; to throw away the reference to the port thatparport_find_base()gives you, useparport_put_port().
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int parport_claim(struct pardevice *dev)¶
claim access to a parallel port device
Parameters
struct pardevice *devpointer 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.
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int parport_claim_or_block(struct pardevice *dev)¶
claim access to a parallel port device
Parameters
struct pardevice *devpointer 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.
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void parport_release(struct pardevice *dev)¶
give up access to a parallel port device
Parameters
struct pardevice *devpointer 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.
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struct pardevice *parport_open(int devnum, const char *name)¶
find a device by canonical device number
Parameters
int devnumcanonical device number
const char *namename 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().
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void parport_close(struct pardevice *dev)¶
close a device opened with
parport_open()
Parameters
struct pardevice *devdevice to close
This is to
parport_open()asparport_unregister_device()is to parport_register_device().
16x50 UART Driver¶
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struct uart_8250_port *serial8250_get_port(int line)¶
retrieve struct uart_8250_port
Parameters
int lineserial 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.
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void serial8250_suspend_port(int line)¶
suspend one serial port
Parameters
int lineserial line number
Suspend one serial port.
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void serial8250_resume_port(int line)¶
resume one serial port
Parameters
int lineserial line number
Resume one serial port.
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int serial8250_register_8250_port(const struct uart_8250_port *up)¶
register a serial port
Parameters
const struct uart_8250_port *upserial 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.
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void serial8250_unregister_port(int line)¶
remove a 16x50 serial port at runtime
Parameters
int lineserial 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.
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enum pwm_polarity¶
polarity of a PWM signal
Constants
PWM_POLARITY_NORMALa high signal for the duration of the duty- cycle, followed by a low signal for the remainder of the pulse period
PWM_POLARITY_INVERSEDa low signal for the duration of the duty- cycle, followed by a high signal for the remainder of the pulse period
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struct pwm_args¶
board-dependent PWM arguments
Definition:
struct pwm_args {
u64 period;
enum pwm_polarity polarity;
};
Members
periodreference period
polarityreference 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.
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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_nsPWM period
duty_length_nsPWM duty cycle
duty_offset_nsoffset 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.
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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
labelname of the PWM device
flagsflags associated with the PWM device
hwpwmper-chip relative index of the PWM device
chipPWM chip providing this PWM device
argsPWM arguments
statelast applied state
lastlast implemented state (for PWM_DEBUG)
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void pwm_get_state(const struct pwm_device *pwm, struct pwm_state *state)¶
retrieve the current PWM state
Parameters
const struct pwm_device *pwmPWM device
struct pwm_state *statestate 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.
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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 *pwmPWM device
struct pwm_state *statestate 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.
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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 *statePWM state to extract the duty cycle from
unsigned int scaletarget 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);
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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 *statePWM state to fill
unsigned int duty_cyclerelative duty cycle value
unsigned int scalescale 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).
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struct pwm_capture¶
PWM capture data
Definition:
struct pwm_capture {
unsigned int period;
unsigned int duty_cycle;
};
Members
periodperiod of the PWM signal (in nanoseconds)
duty_cycleduty cycle of the PWM signal (in nanoseconds)
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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
requestoptional hook for requesting a PWM
freeoptional hook for freeing a PWM
capturecapture and report PWM signal
sizeof_wfhwsize (in bytes) of driver specific waveform presentation
round_waveform_tohwconvert a
struct pwm_waveformto driver specific presentationround_waveform_fromhwconvert a driver specific waveform presentation to
struct pwm_waveformread_waveformread driver specific waveform presentation from hardware
write_waveformwrite driver specific waveform presentation to hardware
applyatomically apply a new PWM config
get_stateget the current PWM state.
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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
devdevice providing the PWMs
opscallbacks for this PWM controller
ownermodule providing this chip
idunique number of this PWM chip
npwmnumber of PWMs controlled by this chip
of_xlaterequest a PWM device given a device tree PWM specifier
atomiccan the driver’s ->apply() be called in atomic context
uses_pwmchip_allocsignals if pwmchip_allow was used to allocate this chip
operationalsignals if the chip can be used (or is already deregistered)
{unnamed_union}anonymous
nonatomic_lockmutex for nonatomic chips
atomic_lockmutex for atomic chips
pwmsarray of PWM devices allocated by the framework
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bool pwmchip_supports_waveform(struct pwm_chip *chip)¶
checks if the given chip supports waveform callbacks
Parameters
struct pwm_chip *chipThe pwm_chip to test
Description
Returns true iff the pwm chip support the waveform functions like
pwm_set_waveform_might_sleep() and pwm_round_waveform_might_sleep()
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int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)¶
change a PWM device configuration
Parameters
struct pwm_device *pwmPWM device
int duty_ns“on” time (in nanoseconds)
int period_nsduration (in nanoseconds) of one cycle
Return
0 on success or a negative error code on failure.
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int pwm_enable(struct pwm_device *pwm)¶
start a PWM output toggling
Parameters
struct pwm_device *pwmPWM device
Return
0 on success or a negative error code on failure.
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void pwm_disable(struct pwm_device *pwm)¶
stop a PWM output toggling
Parameters
struct pwm_device *pwmPWM device
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bool pwm_might_sleep(struct pwm_device *pwm)¶
is
pwm_apply_atomic()supported?
Parameters
struct pwm_device *pwmPWM device
Return
false if pwm_apply_atomic() can be called from atomic context.
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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 *pwmPWM device
struct pwm_waveform *wfwaveform 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.
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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 *pwmPWM device
struct pwm_waveform *wfoutput 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.
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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 *pwmPWM device
const struct pwm_waveform *wfThe waveform to apply
bool exactIf 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.
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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 *pwmPWM device
const struct pwm_state *statenew state to apply
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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 *pwmPWM device
const struct pwm_state *statenew state to apply
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int pwm_get_state_hw(struct pwm_device *pwm, struct pwm_state *state)¶
get the current PWM state from hardware
Parameters
struct pwm_device *pwmPWM device
struct pwm_state *statestate 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.
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int pwm_adjust_config(struct pwm_device *pwm)¶
adjust the current PWM config to the PWM arguments
Parameters
struct pwm_device *pwmPWM 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.
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struct pwm_device *pwm_get(struct device *dev, const char *con_id)¶
look up and request a PWM device
Parameters
struct device *devdevice for PWM consumer
const char *con_idconsumer 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.
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void pwm_put(struct pwm_device *pwm)¶
release a PWM device
Parameters
struct pwm_device *pwmPWM device
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struct pwm_device *devm_pwm_get(struct device *dev, const char *con_id)¶
resource managed
pwm_get()
Parameters
struct device *devdevice for PWM consumer
const char *con_idconsumer 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.
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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 *devdevice for PWM consumer
struct fwnode_handle *fwnodefirmware node to get the PWM from
const char *con_idconsumer 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.
Parameters
struct pwm_chip *chipthe PWM chip to add
struct module *ownerreference 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.
Parameters
struct pwm_chip *chipthe PWM chip to remove
Description
Removes a PWM chip.