diff options
Diffstat (limited to 'Documentation/pwm.txt')
| -rw-r--r-- | Documentation/pwm.txt | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt index ca895fd211e4..789b27c6ec99 100644 --- a/Documentation/pwm.txt +++ b/Documentation/pwm.txt @@ -42,9 +42,26 @@ variants of these functions, devm_pwm_get() and devm_pwm_put(), also exist. After being requested, a PWM has to be configured using: -int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns); +int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state); -To start/stop toggling the PWM output use pwm_enable()/pwm_disable(). +This API controls both the PWM period/duty_cycle config and the +enable/disable state. + +The pwm_config(), pwm_enable() and pwm_disable() functions are just wrappers +around pwm_apply_state() and should not be used if the user wants to change +several parameter at once. For example, if you see pwm_config() and +pwm_{enable,disable}() calls in the same function, this probably means you +should switch to pwm_apply_state(). + +The PWM user API also allows one to query the PWM state with pwm_get_state(). + +In addition to the PWM state, the PWM API also exposes PWM arguments, which +are the reference PWM config one should use on this PWM. +PWM arguments are usually platform-specific and allows the PWM user to only +care about dutycycle relatively to the full period (like, duty = 50% of the +period). struct pwm_args contains 2 fields (period and polarity) and should +be used to set the initial PWM config (usually done in the probe function +of the PWM user). PWM arguments are retrieved with pwm_get_args(). Using PWMs with the sysfs interface ----------------------------------- @@ -105,6 +122,15 @@ goes low for the remainder of the period. Conversely, a signal with inversed polarity starts low for the duration of the duty cycle and goes high for the remainder of the period. +Drivers are encouraged to implement ->apply() instead of the legacy +->enable(), ->disable() and ->config() methods. Doing that should provide +atomicity in the PWM config workflow, which is required when the PWM controls +a critical device (like a regulator). + +The implementation of ->get_state() (a method used to retrieve initial PWM +state) is also encouraged for the same reason: letting the PWM user know +about the current PWM state would allow him to avoid glitches. + Locking ------- |