On Wed, Jun 22, 2016 at 10:04:22AM +0200, Boris Brezillon wrote:
> From 0610f7e24976e176054bce20445ff42d8aea9513 Mon Sep 17 00:00:00 2001
> From: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
> Date: Wed, 22 Jun 2016 09:25:14 +0200
> Subject: [PATCH] pwm: Fix pwm_apply_args()
>
> Commit 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic
> updates"), implemented pwm_disable() as a wrapper around
> pwm_apply_state(), and then, commit ef2bf4997f7d ("pwm: Improve args
> checking in pwm_apply_state()") added missing checks on the ->period
> value in pwm_apply_state() to ensure we were not passing inappropriate
> values to the ->config() or ->apply() methods.
>
> The conjunction of these 2 commits led to a case where pwm_disable()
> was no longer succeeding, thus preventing the polarity setting done
> in pwm_apply_args().
>
> Set a valid period in pwm_apply_args() to ensure polarity setting
> won't be rejected.
>
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Suggested-by: Brian Norris <briannorris@xxxxxxxxxxxx>
> Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")
> ---
> include/linux/pwm.h | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> index 908b67c847cd..c038ae36b10e 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm)
>
> static inline void pwm_apply_args(struct pwm_device *pwm)
> {
> + struct pwm_state state = { };
> +
> /*
> * PWM users calling pwm_apply_args() expect to have a fresh config
> * where the polarity and period are set according to pwm_args info.
> @@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm)
> * at startup (even if they are actually enabled), thus authorizing
> * polarity setting.
> *
> - * Instead of setting ->enabled to false, we call pwm_disable()
> - * before pwm_set_polarity() to ensure that everything is configured
> - * as expected, and the PWM is really disabled when the user request
> - * it.
I was confused by this original text when reading it the first time. I
like the replacement text and implementation, as it seems to make more
sense.
> + * To fulfill this requirement, we apply a new state which disables
> + * the PWM device and set the reference period and polarity config.
> *
> * Note that PWM users requiring a smooth handover between the
> * bootloader and the kernel (like critical regulators controlled by
> * PWM devices) will have to switch to the atomic API and avoid calling
> * pwm_apply_args().
> */
> - pwm_disable(pwm);
> - pwm_set_polarity(pwm, pwm->args.polarity);
Notably, you're dropping the 'if (!pwm) { }' safety checks that are part
of pwm_disable() and pwm_set_polarity(). But I don't think there should
be any users relying on that.
> +
> + state.enabled = false;
> + state.polarity = pwm->args.polarity;
> + state.period = pwm->args.period;
> +
> + pwm_apply_state(pwm, &state);
> }
>
> struct pwm_lookup {
Reviewed-by: Brian Norris <briannorris@xxxxxxxxxxxx>
