Re: [PATCH] pwm: sysfs: Do not apply state to already disabled PWMs

[Brian Norris <briannorris@chromium.org>]

Hi,

On Fri, May 12, 2023 at 06:47:36PM +0200, Marek Vasut wrote:
> If the PWM is exported but not enabled, do not call pwm_class_apply_state().
> First of all, in this case, period may still be unconfigured and this would
> make pwm_class_apply_state() return -EINVAL, and then suspend would fail.
> Second, it makes little sense to apply state onto PWM that is not enabled
> before suspend.
> 
> 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
> ...
> "
> 
> Do not call pwm_class_apply_state() in case the PWM is disabled
> to fix this issue.
> 
> Fixes: 7fd4edc57bbae ("pwm: sysfs: Add suspend/resume support")

My first thought was that this still belongs as:

Fixes: ef2bf4997f7d ("pwm: Improve args checking in pwm_apply_state()")

but then I realized sysfs suspend/resume support was added *after* that,
so indeed, your Fixes tag makes the most sense.

And yes, I think this solution (addressing sysfs.c directly) is best
too:

Reviewed-by: Brian Norris <briannorris@chromium.org>

Side question: I wonder if this belongs in linux-stable. It's definitely
a bug fix, but the bug has been around a while, with a
{under,non}-specified ABI, and it's easy enough to work around I
suppose. But inevitably, *any* patch with a Fixes tag gets picked up by
somebody's cherry-picking bot, so maybe it doesn't matter...
...Anyway, I guess I'm saying it's probably going to go to linux-stable,
whether we want it to or not; and maybe that's OK :)

Thanks,
Brian

> 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/sysfs.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)