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Commit c571123c authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by Thierry Reding
Browse files

pwm: Standardize document format 



Each text file under Documentation follows a different format. Some
don't even have titles!

Change its representation to follow the adopted standard, using ReST
markup for it to be parseable by Sphinx:

- mark document title;
- mark literal blocks;
- better format the parameters.

Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent 2ea659a9

Documentation/pwm.txt

+28 −18
Original line number Diff line number Diff line 
======================================

Pulse Width Modulation (PWM) interface

======================================



This provides an overview about the Linux PWM interface
@@ -16,7 +18,7 @@ Users of the legacy PWM API use unique IDs to refer to PWM devices. 


Instead of referring to a PWM device via its unique ID, board setup code

should instead register a static mapping that can be used to match PWM

consumers to providers, as given in the following example:

consumers to providers, as given in the following example::



	static struct pwm_lookup board_pwm_lookup[] = {

		PWM_LOOKUP("tegra-pwm", 0, "pwm-backlight", NULL,
@@ -40,7 +42,7 @@ New users should use the pwm_get() function and pass to it the consumer 
device or a consumer name. pwm_put() is used to free the PWM device. Managed

variants of these functions, devm_pwm_get() and devm_pwm_put(), also exist.



After being requested, a PWM has to be configured using:

After being requested, a PWM has to be configured using::



	int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state);
@@ -72,11 +74,14 @@ interface is provided to use the PWMs from userspace. It is exposed at 
pwmchipN, where N is the base of the PWM chip. Inside the directory you

will find:



npwm - The number of PWM channels this chip supports (read-only).

  npwm

    The number of PWM channels this chip supports (read-only).



export - Exports a PWM channel for use with sysfs (write-only).

  export

    Exports a PWM channel for use with sysfs (write-only).



unexport - Unexports a PWM channel from sysfs (write-only).

  unexport

   Unexports a PWM channel from sysfs (write-only).



The PWM channels are numbered using a per-chip index from 0 to npwm-1.
@@ -84,21 +89,26 @@ When a PWM channel is exported a pwmX directory will be created in the 
pwmchipN directory it is associated with, where X is the number of the

channel that was exported. The following properties will then be available:



period - The total period of the PWM signal (read/write).

  period

    The total period of the PWM signal (read/write).

    Value is in nanoseconds and is the sum of the active and inactive

    time of the PWM.



duty_cycle - The active time of the PWM signal (read/write).

  duty_cycle

    The active time of the PWM signal (read/write).

    Value is in nanoseconds and must be less than the period.



polarity - Changes the polarity of the PWM signal (read/write).

  polarity

    Changes the polarity of the PWM signal (read/write).

    Writes to this property only work if the PWM chip supports changing

    the polarity. The polarity can only be changed if the PWM is not

    enabled. Value is the string "normal" or "inversed".



enable - Enable/disable the PWM signal (read/write).

	0 - disabled

	1 - enabled

  enable

    Enable/disable the PWM signal (read/write).



	- 0 - disabled

	- 1 - enabled



Implementing a PWM driver

-------------------------