Re: [PATCH] pwm: core: Permit unset period when applying configuration of disabled PWMs

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

[-- Attachment #1: Type: text/plain, Size: 2656 bytes --]

Hello Marek,

On Thu, May 11, 2023 at 08:18:53PM +0200, Marek Vasut wrote:
> In case the PWM is not enabled, the period can still be left unconfigured,
> i.e. zero . Currently the pwm_class_apply_state() errors out in such a case.
> This e.g. makes suspend fail on systems where pwmchip has been exported via
> sysfs interface, but left unconfigured before suspend occurred.
> 
> Failing case:
> "
> $ echo 1 > /sys/class/pwm/pwmchip4/export
> $ echo mem > /sys/power/state
> ...
> pwm pwmchip4: PM: dpm_run_callback(): pwm_class_suspend+0x1/0xa8 returns -22
> pwm pwmchip4: PM: failed to suspend: error -22
> PM: Some devices failed to suspend, or early wake event detected
> "
> 
> Working case:
> "
> $ echo 1 > /sys/class/pwm/pwmchip4/export
> $ echo 100 > /sys/class/pwm/pwmchip4/pwm1/period
> $ echo 10 > /sys/class/pwm/pwmchip4/pwm1/duty_cycle
> $ echo mem > /sys/power/state
> ...
> "
> 
> Permit unset period in pwm_class_apply_state() in case the PWM is disabled
> to fix this issue.
> 
> Fixes: ef2bf4997f7d ("pwm: Improve args checking in pwm_apply_state()")
> Signed-off-by: Marek Vasut <marex@denx.de>
> ---
> Cc: Brian Norris <briannorris@chromium.org>
> Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> Cc: Thierry Reding <thierry.reding@gmail.com>
> Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> Cc: linux-pwm@vger.kernel.org
> ---
>  drivers/pwm/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 3dacceaef4a9b..87252b70f1c81 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -510,8 +510,8 @@ int pwm_apply_state(struct pwm_device *pwm, const struct pwm_state *state)
>  	 */
>  	might_sleep();
>  
> -	if (!pwm || !state || !state->period ||
> -	    state->duty_cycle > state->period)
> +	if (!pwm || !state || (state->enabled &&
> +	    (!state->period || state->duty_cycle > state->period)))

While I tend to agree that the checks about period and duty_cycle are
(somewhat) irrelevant if enabled == false, I fear we'd break assumptions
here as some drivers configure duty_cycle/period in hardware even with
.enabled == false, and so proably rely on period > 0 and duty_cycle <=
period.

Another approach would be to skip pwm_apply_state() in
pwm_class_suspend() if the state is already disabled. That one sounds
safer.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]