linux-kernel - Re: [regression] stm32mp1xx based targets stopped entering suspend if pwm-leds exist

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Date: Wed, 6 Mar 2024 09:18:04 +0100
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Linux regressions mailing list <regressions@...ts.linux.dev>
Cc: Lee Jones <lee@...nel.org>, linux-leds@...r.kernel.org, 
	linux-pwm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [regression] stm32mp1xx based targets stopped entering suspend
 if pwm-leds exist

Hello,

On Wed, Mar 06, 2024 at 08:05:15AM +0100, Linux regression tracking (Thorsten Leemhuis) wrote:
> Hi, Thorsten here, the Linux kernel's regression tracker.
> 
> Uwe, I noticed a report about a regression in bugzilla.kernel.org that
> apparently is caused by a change of yours. As many (most?) kernel
> developers don't keep an eye on it, I decided to forward it by mail.
> 
> Note, you have to use bugzilla to reach the reporter, as I sadly[1] can
> not CCed them in mails like this.
> 
> Quoting from https://bugzilla.kernel.org/show_bug.cgi?id=218559 :
> 
> > Commit 76fe464c8e64e71b2e4af11edeef0e5d85eeb6aa ("leds: pwm: Don't
> > disable the PWM when the LED should be off") prevents stm32mp1xx based
> > targets from entering suspend if pwm-leds exist, as the stm32 PWM driver
> > refuses to enter suspend if any PWM channels are still active ("PWM 0
> > still in use by consumer" see stm32_pwm_suspend in drivers/pwm/stm32-pwm.c).
> > 
> > Reverting the mentioned commit fixes this behaviour but I'm not
> > certain if this is a problem with stm32-pwm or pwm-leds (what is the
> > usual behaviour for suspend with active PWM channels?).

I'd assume the following patch fixes this report. I didn't test it
though.

Best regards
Uwe

---->8----
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Subject: [PATCH] leds: pwm: Disable PWM when going to suspend

On stm32mp1xx based machines (and others) a PWM consumer has to disable
the PWM because an enabled PWM refuses to suspend. So check the
LED_SUSPENDED flag and depending on that set the .enabled property.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=218559
Fixes: 76fe464c8e64 ("leds: pwm: Don't disable the PWM when the LED should be off")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
 drivers/leds/leds-pwm.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
index 4e3936a39d0e..e1b414b40353 100644
--- a/drivers/leds/leds-pwm.c
+++ b/drivers/leds/leds-pwm.c
@@ -53,7 +53,13 @@ static int led_pwm_set(struct led_classdev *led_cdev,
 		duty = led_dat->pwmstate.period - duty;
 
 	led_dat->pwmstate.duty_cycle = duty;
-	led_dat->pwmstate.enabled = true;
+	/*
+	 * Disabling a PWM doesn't guarantee that it emits the inactive level.
+	 * So keep it on. Only for suspending the PWM should be disabled because
+	 * otherwise it refuses to suspend. The possible downside is that the
+	 * LED might stay (or even go) on.
+	 */
+	led_dat->pwmstate.enabled = !(led_cdev->flags & LED_SUSPENDED);
 	return pwm_apply_might_sleep(led_dat->pwm, &led_dat->pwmstate);
 }

base-commit: 15facbd7bd3dbfa04721cb71e69954eb4686cb9e
---->8----

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

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