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| -rw-r--r-- | Documentation/pwm.txt | 46 |
1 files changed, 28 insertions, 18 deletions
diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt index 789b27c6ec99..8fbf0aa3ba2d 100644 --- a/Documentation/pwm.txt +++ b/Documentation/pwm.txt @@ -1,4 +1,6 @@ +====================================== 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, @@ -40,9 +42,9 @@ 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); + int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state); This API controls both the PWM period/duty_cycle config and the enable/disable 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). - Value is in nanoseconds and is the sum of the active and inactive - time of the PWM. + 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). - Value is in nanoseconds and must be less than the period. + 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). - 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". + 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 ------------------------- |