Re: (EXT) [PATCH] pwm: Document that the pinstate of a disabled PWM isn't reliable

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Am Dienstag, 17. Mai 2022, 17:05:55 CEST schrieb Uwe Kleine-König:
> Some (most?) drivers emit the inactive state when the PWM is disabled.
> However there are exceptions, so document that a consumer better doesn't
> depend on this behaviour.
> 
> Some known exceptions:
> 
>   - imx27 emits 0 independent of the configured polarity
>   - mxs just drives the output to the last emitted state.
>   - iqs620a makes the output tristated on disable, so an external
>     pull-down would be required.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> ---
>  Documentation/driver-api/pwm.rst | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/driver-api/pwm.rst
> b/Documentation/driver-api/pwm.rst index ccb06e485756..fd26c3d895b6 100644
> --- a/Documentation/driver-api/pwm.rst
> +++ b/Documentation/driver-api/pwm.rst
> @@ -49,6 +49,12 @@ After being requested, a PWM has to be configured using::
> 
>  This API controls both the PWM period/duty_cycle config and the
>  enable/disable state.
> +
> +As a consumer, don't rely on the output's state for a disabled PWM. If it's
> +easily possible, drivers are supposed to emit the inactive state, but some
> +drivers cannot. If you rely on getting the inactive state, use
> .duty_cycle=0, +.enabled=true.
> +
>  There is also a usage_power setting: If set, the PWM driver is only
> required to maintain the power output but has more freedom regarding signal
> form. If supported by the driver, the signal can be optimized, for example
> to improve

Acked-by: Alexander Stein <alexander.stein@ew.tq-group.com>