Parallel Port Devices¶

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)

Description

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

Description

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

Description

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

Description

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

Description

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)

Description

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

Description

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()

Description

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

Description

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

Description

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

Description

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

Description

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

Description

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_device(struct parport *port, const char *name, int (*pf)(void*), void (*kf)(void*), void (*irq_func)(void*), int flags, void *handle)¶: 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
int (*)(void *) pf: preemption callback
void (*)(void *) kf: kick callback (wake-up)
void (*)(void *) irq_func: interrupt handler
int flags: registration flags
void * handle: data for callback functions

Description

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 name is allocated by the caller and must not be deallocated until the caller calls parport_unregister_device for that device.

The preemption callback function, pf, is called when this device driver has claimed access to the port but another device driver wants to use it. It is given handle 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, pf can be NULL.

The wake-up (“kick”) callback function, kf, 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, kf 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

Description

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

Description

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

Description

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

Description

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

Description

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

Description

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

Description

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

Description

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

16x50 UART Driver¶

void uart_update_timeout(struct uart_port *port, unsigned int cflag, unsigned int baud)¶: update per-port FIFO timeout.

Parameters

struct uart_port * port: uart_port structure describing the port
unsigned int cflag: termios cflag value
unsigned int baud: speed of the port

Description

Set the port FIFO timeout value. The cflag value should reflect the actual hardware settings.

unsigned int uart_get_baud_rate(struct uart_port *port, struct ktermios *termios, struct ktermios *old, unsigned int min, unsigned int max)¶: return baud rate for a particular port

Parameters

struct uart_port * port: uart_port structure describing the port in question.
struct ktermios * termios: desired termios settings.
struct ktermios * old: old termios (or NULL)
unsigned int min: minimum acceptable baud rate
unsigned int max: maximum acceptable baud rate

Description

Decode the termios structure into a numeric baud rate, taking account of the magic 38400 baud rate (with spd_* flags), and mapping the B0 rate to 9600 baud.

If the new baud rate is invalid, try the old termios setting. If it’s still invalid, we try 9600 baud.

Update the termios structure to reflect the baud rate we’re actually going to be using. Don’t do this for the case where B0 is requested (“hang up”).

unsigned int uart_get_divisor(struct uart_port *port, unsigned int baud)¶: return uart clock divisor

Parameters

struct uart_port * port: uart_port structure describing the port.
unsigned int baud: desired baud rate

Description

Calculate the uart clock divisor for the port.

void uart_console_write(struct uart_port *port, const char *s, unsigned int count, void (*putchar)(struct uart_port*, int))¶: write a console message to a serial port

Parameters

struct uart_port * port: the port to write the message
const char * s: array of characters
unsigned int count: number of characters in string to write
void (*)(struct uart_port *, int) putchar: function to write character to port

int uart_parse_earlycon(char *p, unsigned char *iotype, resource_size_t *addr, char **options)¶: Parse earlycon options

Parameters

char * p: ptr to 2nd field (ie., just beyond ‘<name>,’)
unsigned char * iotype: ptr for decoded iotype (out)
resource_size_t * addr: ptr for decoded mapbase/iobase (out)
char ** options: ptr for <options> field; NULL if not present (out)

Description

Decodes earlycon kernel command line parameters of the form
earlycon=<name>,io|mmio|mmio16|mmio32|mmio32be|mmio32native,<addr>,<options> console=<name>,io|mmio|mmio16|mmio32|mmio32be|mmio32native,<addr>,<options>

The optional form

earlycon=<name>,0x<addr>,<options> console=<name>,0x<addr>,<options>

is also accepted; the returned iotype will be UPIO_MEM.

Returns 0 on success or -EINVAL on failure

void uart_parse_options(const char *options, int *baud, int *parity, int *bits, int *flow)¶: Parse serial port baud/parity/bits/flow control.

Parameters

const char * options: pointer to option string
int * baud: pointer to an ‘int’ variable for the baud rate.
int * parity: pointer to an ‘int’ variable for the parity.
int * bits: pointer to an ‘int’ variable for the number of data bits.
int * flow: pointer to an ‘int’ variable for the flow control character.

Description

uart_parse_options decodes a string containing the serial console options. The format of the string is <baud><parity><bits><flow>, eg: 115200n8r

int uart_set_options(struct uart_port *port, struct console *co, int baud, int parity, int bits, int flow)¶: setup the serial console parameters

Parameters

struct uart_port * port: pointer to the serial ports uart_port structure
struct console * co: console pointer
int baud: baud rate
int parity: parity character - ‘n’ (none), ‘o’ (odd), ‘e’ (even)
int bits: number of data bits
int flow: flow control character - ‘r’ (rts)

int uart_register_driver(struct uart_driver *drv)¶: register a driver with the uart core layer

Parameters

struct uart_driver * drv: low level driver structure

Description

Register a uart driver with the core driver. We in turn register with the tty layer, and initialise the core driver per-port state.

We have a proc file in /proc/tty/driver which is named after the normal driver.

drv->port should be NULL, and the per-port structures should be registered using uart_add_one_port after this call has succeeded.

void uart_unregister_driver(struct uart_driver *drv)¶: remove a driver from the uart core layer

Parameters

struct uart_driver * drv: low level driver structure

Description

Remove all references to a driver from the core driver. The low level driver must have removed all its ports via the uart_remove_one_port() if it registered them with uart_add_one_port(). (ie, drv->port == NULL)

int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)¶: attach a driver-defined port structure

Parameters

struct uart_driver * drv: pointer to the uart low level driver structure for this port
struct uart_port * uport: uart port structure to use for this port.

Description

This allows the driver to register its own uart_port structure with the core driver. The main purpose is to allow the low level uart drivers to expand uart_port, rather than having yet more levels of structures.

int uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)¶: detach a driver defined port structure

Parameters

struct uart_driver * drv: pointer to the uart low level driver structure for this port
struct uart_port * uport: uart port structure for this port

Description

This unhooks (and hangs up) the specified port structure from the core driver. No further calls will be made to the low-level code for this port.

void uart_handle_dcd_change(struct uart_port *uport, unsigned int status)¶: handle a change of carrier detect state

Parameters

struct uart_port * uport: uart_port structure for the open port
unsigned int status: new carrier detect status, nonzero if active

Description

Caller must hold uport->lock

void uart_handle_cts_change(struct uart_port *uport, unsigned int status)¶: handle a change of clear-to-send state

Parameters

struct uart_port * uport: uart_port structure for the open port
unsigned int status: new clear to send status, nonzero if active

Description

Caller must hold uport->lock

void uart_insert_char(struct uart_port *port, unsigned int status, unsigned int overrun, unsigned int ch, unsigned int flag)¶: push a char to the uart layer

Parameters

struct uart_port * port: corresponding port
unsigned int status: state of the serial port RX buffer (LSR for 8250)
unsigned int overrun: mask of overrun bits in status
unsigned int ch: character to push
unsigned int flag: flag for the character (see TTY_NORMAL and friends)

Description

User is responsible to call tty_flip_buffer_push when they are done with insertion.

bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch)¶: Enables SysRq from serial line

Parameters

struct uart_port * port: uart_port structure where char(s) after BREAK met
unsigned int ch: new character in the sequence after received BREAK

Description

Enables magic SysRq when the required sequence is met on port (see CONFIG_MAGIC_SYSRQ_SERIAL_SEQUENCE).

Returns false if ch is out of enabling sequence and should be handled some other way, true if ch was consumed.

void uart_get_rs485_mode(struct device *dev, struct serial_rs485 *rs485conf)¶: retrieve rs485 properties for given uart

Parameters

struct device * dev: uart device
struct serial_rs485 * rs485conf: output parameter

Description

This function implements the device tree binding described in Documentation/devicetree/bindings/serial/rs485.txt.

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

Description

Suspend one serial port.

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

Parameters

int line: serial line number

Description

Resume one serial port.

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

Parameters

struct uart_8250_port * up: serial port template

Description

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

Description

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

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 {
  unsigned int 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_device: PWM channel object

Definition

struct pwm_device {
  const char *label;
  unsigned long flags;
  unsigned int hwpwm;
  unsigned int pwm;
  struct pwm_chip *chip;
  void *chip_data;
  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
pwm: global index of the PWM device
chip: PWM chip providing this PWM device
chip_data: chip-private data associated with the 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

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

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_state(). 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_state().

->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_state() 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_state(pwm, state);

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

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);
  int (*apply)(struct pwm_chip *chip, struct pwm_device *pwm, const struct pwm_state *state);
  void (*get_state)(struct pwm_chip *chip, struct pwm_device *pwm, struct pwm_state *state);
  struct module *owner;
  int (*config)(struct pwm_chip *chip, struct pwm_device *pwm, int duty_ns, int period_ns);
  int (*set_polarity)(struct pwm_chip *chip, struct pwm_device *pwm, enum pwm_polarity polarity);
  int (*enable)(struct pwm_chip *chip, struct pwm_device *pwm);
  void (*disable)(struct pwm_chip *chip, struct pwm_device *pwm);
};

Members

request: optional hook for requesting a PWM
free: optional hook for freeing a PWM
capture: capture and report PWM signal
apply: atomically apply a new PWM config
get_state: get the current PWM state. This function is only called once per PWM device when the PWM chip is registered.
owner: helps prevent removal of modules exporting active PWMs
config: configure duty cycles and period length for this PWM
set_polarity: configure the polarity of this PWM
enable: enable PWM output toggling
disable: disable PWM output toggling

struct pwm_chip: abstract a PWM controller

Definition

struct pwm_chip {
  struct device *dev;
  const struct pwm_ops *ops;
  int base;
  unsigned int npwm;
  struct pwm_device * (*of_xlate)(struct pwm_chip *pc, const struct of_phandle_args *args);
  unsigned int of_pwm_n_cells;
  struct list_head list;
  struct pwm_device *pwms;
};

Members

dev: device providing the PWMs
ops: callbacks for this PWM controller
base: number of first PWM controlled by this chip
npwm: number of PWMs controlled by this chip
of_xlate: request a PWM device given a device tree PWM specifier
of_pwm_n_cells: number of cells expected in the device tree PWM specifier
list: list node for internal use
pwms: array of PWM devices allocated by the framework

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)

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

int pwm_set_chip_data(struct pwm_device *pwm, void *data)¶: set private chip data for a PWM

Parameters

struct pwm_device * pwm: PWM device
void * data: pointer to chip-specific data

Return

0 on success or a negative error code on failure.

void *pwm_get_chip_data(struct pwm_device *pwm)¶: get private chip data for a PWM

Parameters

struct pwm_device * pwm: PWM device

Return

A pointer to the chip-private data for the PWM device.

int pwmchip_add_with_polarity(struct pwm_chip *chip, enum pwm_polarity polarity)¶: register a new PWM chip

Parameters

struct pwm_chip * chip: the PWM chip to add
enum pwm_polarity polarity: initial polarity of PWM channels

Description

Register a new PWM chip. If chip->base < 0 then a dynamically assigned base will be used. The initial polarity for all channels is specified by the polarity parameter.

Return

0 on success or a negative error code on failure.

int pwmchip_add(struct pwm_chip *chip)¶: register a new PWM chip

Parameters

struct pwm_chip * chip: the PWM chip to add

Description

Register a new PWM chip. If chip->base < 0 then a dynamically assigned base will be used. The initial polarity for all channels is normal.

Return

0 on success or a negative error code on failure.

int 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. This function may return busy if the PWM chip provides a PWM device that is still requested.

Return

0 on success or a negative error code on failure.

struct pwm_device *pwm_request(int pwm, const char *label)¶: request a PWM device

Parameters

int pwm: global PWM device index
const char * label: PWM device label

Description

This function is deprecated, use pwm_get() instead.

Return

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

struct pwm_device *pwm_request_from_chip(struct pwm_chip *chip, unsigned int index, const char *label)¶: request a PWM device relative to a PWM chip

Parameters

struct pwm_chip * chip: PWM chip
unsigned int index: per-chip index of the PWM to request
const char * label: a literal description string of this PWM

Return

A pointer to the PWM device at the given index of the given PWM chip. A negative error code is returned if the index is not valid for the specified PWM chip or if the PWM device cannot be requested.

void pwm_free(struct pwm_device *pwm)¶: free a PWM device

Parameters

struct pwm_device * pwm: PWM device

Description

This function is deprecated, use pwm_put() instead.

int pwm_apply_state(struct pwm_device *pwm, const struct pwm_state *state)¶: atomically apply a new state to a PWM device

Parameters

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

int pwm_capture(struct pwm_device *pwm, struct pwm_capture *result, unsigned long timeout)¶: capture and report a PWM signal

Parameters

struct pwm_device * pwm: PWM device
struct pwm_capture * result: structure to fill with capture result
unsigned long timeout: time to wait, in milliseconds, before giving up on capture

Return

0 on success or a negative error code on failure.

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 *of_pwm_get(struct device *dev, struct device_node *np, const char *con_id)¶: request a PWM via the PWM framework

Parameters

struct device * dev: device for PWM consumer
struct device_node * np: device node to get the PWM from
const char * con_id: consumer name

Description

Returns the PWM device parsed from the phandle and index specified in the “pwms” property of a device tree node or a negative error-code on failure. Values parsed from the device tree are stored in the returned PWM device object.

If con_id is NULL, the first PWM device listed in the “pwms” property will be requested. Otherwise the “pwm-names” property is used to do a reverse lookup of the PWM index. This also means that the “pwm-names” property becomes mandatory for devices that look up the PWM device via the con_id parameter.

Return

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

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_of_pwm_get(struct device *dev, struct device_node *np, const char *con_id)¶: resource managed of_pwm_get()

Parameters

struct device * dev: device for PWM consumer
struct device_node * np: device node to get the PWM from
const char * con_id: consumer name

Description

This function performs like of_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.

void devm_pwm_put(struct device *dev, struct pwm_device *pwm)¶: resource managed pwm_put()

Parameters

struct device * dev: device for PWM consumer
struct pwm_device * pwm: PWM device

Description

Release a PWM previously allocated using devm_pwm_get(). Calling this function is usually not needed because devm-allocated resources are automatically released on driver detach.

Parallel Port Devices¶

16x50 UART Driver¶

Pulse-Width Modulation (PWM)¶

The Linux Kernel

Navigation

Related Topics