Subject: [[PATCH]] drivers: leds/trigger: system cannot enter suspend

From: [email-masked] (Pavel Machek)
Date: Tue, 6 Jun 2017 22:34:05 +0200

On Tue 2017-06-06 15:19:23, Grygorii Strashko wrote:
> 
> 
> On 06/06/2017 03:05 PM, Jacek Anaszewski wrote:
> > On 06/06/2017 09:25 PM, Pavel Machek wrote:
> >> On Tue 2017-06-06 10:36:36, Zhang Bo wrote:
> >>> System cannot enter suspend mode because of heartbeat led trigger.
> >>> In autosleep_wq, try_to_suspend function will try to enter suspend
> >>> mode in specific period. it will get wakeup_count then call pm_notifier
> >>> chain callback function and freeze processes.
> >>> Heartbeat_pm_notifier is called and it call led_trigger_unregister to
> >>> change the trigger of led device to none. It will send uevent
> >>
> >> Why is heartbeat_pm_notifier calling led_trigger_unregister? That
> >> sounds like a bug.
> > 
> > I suggest using git blame. The commit message adding this code is pretty
> > informative.
> > 
> 
> In my opinion original commit do not contain ehough info about root cause 
> of the problem (commit 5ab92a7cb "leds: handle suspend/resume in heartbeat trigger")
> 
> "The following phenomena was observed: when suspending the
>     system, sometimes the heartbeat LED was left on, glowing and
>     wasting power while the rest of the system is asleep, also
>     disturbing power dissapation measures on the odd suspend
>     cycle when it's left on.
> "
> 
> But why is this happen? In general, leds expected to be switched off during suspend
> from led_classdev_suspend() which sets LED_SUSPENDED and so blocks 
> led_set_brightness_nosleep() and led_set_brightness_sync().
> 
> I think, there was some race between led_classdev_suspend() and
> set_brightness_work and led_heartbeat_function() which is timer callback.
> 
> So, In my opinion, real solution is to remove heartbeat_pm_notifier() and ensure
> that LED_SUSPENDED flag is processed correctly during suspend. Another option could be
> to use syscore_ops as it's done in ledtrig-cpu.c.

Agreed. LED staying on is not good enough reason to do
led_trigger_unregister() and then add more suspend/resume code to make
sure it does not break suspend.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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