[[PATCH v2]] drivers: leds/trigger: system cannot enter suspend
Bruce Zhang
bo.zhang at nxp.com
Thu Jun 8 19:57:49 PDT 2017
Hi Jacek,
I think that no change need to make for __led_set_brightness() and __led_set_brightness_blocking() function. Because led_classdev_suspend() need to turn off LED with these API. set_brightness_delayed() is the same level API as __led_set_brightness(). No need to add LED_SUSPENDED checking as well.
Best Regards,
Bo
-----Original Message-----
From: Jacek Anaszewski [mailto:jacek.anaszewski at gmail.com]
Sent: Friday, June 09, 2017 4:28 AM
To: Bruce Zhang <bo.zhang at nxp.com>; Pavel Machek <pavel at ucw.cz>; Linus Walleij <linus.walleij at linaro.org>
Cc: Ulf Hansson <ulf.hansson at linaro.org>; linux-arm-kernel at lists.infradead.org; Richard Purdie <rpurdie at rpsys.net>; linux-leds at vger.kernel.org
Subject: Re: [[PATCH v2]] drivers: leds/trigger: system cannot enter suspend
Hi Bruce,
On 06/08/2017 04:57 AM, Bruce Zhang wrote:
> Hi,
>
> As suspend/resume procedure is as below:
> pm_notifier_call_chain(PM_SUSPEND_PREPARE)->device suspend -> syscore suspend -> enter suspend mode -> syscore resume -> device resume -> pm_notifier_call_chain(PM_POST_SUSPEND).
> If led brightness control depends on other device/hardware (such as I2C), the LED turn off action should be earlier than device suspend. pm_notifier may be a suitable method to turn off LED.
OK, so I agree that the most proper fix to the discussed problem would be ignoring brightness setting requests after suspend, as Pavel suggested.
led_classdev_suspend() already turns the LED off and
led_classdev_resume() brings the brightness back.
Also led_set_brightness_nosleep() and led_set_brightness_sync() don't propagate brightness change to the driver if LED_SUSPENDED is set.
There are two problems though:
1. __led_set_brightness() and __led_set_brightness_blocking() don't
check the flag, and they can be called from set_brightness_delayed(),
that was already queued at the time of setting LED_SUSPENDED flag.
2. LED_SUSPENDED flag is accessed in a non-atomic way.
The solution as I see it would be respectively:
1. Return from __led_set_brightness() and
__led_set_brightness_blocking() if LED_SUSPENDED is set.
2. Switch to accessing struct led_classdev's flags with use of
bitops. Fortunately those flags are mainly set prior LED class
device registration and only LED_SYSFS_DISABLE, LED_SUSPENDED
and LED_UNREGISTERING are accessed afterwards, and only in the LED
core, so only those places would have to be modified.
Best regards,
Jacek Anaszewski
> -----Original Message-----
> From: Pavel Machek [mailto:pavel at ucw.cz]
> Sent: Wednesday, June 07, 2017 6:31 PM
> To: Linus Walleij <linus.walleij at linaro.org>
> Cc: Bruce Zhang <bo.zhang at nxp.com>; Ulf Hansson
> <ulf.hansson at linaro.org>; linux-arm-kernel at lists.infradead.org; Jacek
> Anaszewski <jacek.anaszewski at gmail.com>; Richard Purdie
> <rpurdie at rpsys.net>; linux-leds at vger.kernel.org
> Subject: Re: [[PATCH v2]] drivers: leds/trigger: system cannot enter
> suspend
>
> Hi!
>
> On Wed 2017-06-07 11:46:10, Linus Walleij wrote:
>> On Wed, Jun 7, 2017 at 9:12 AM, Pavel Machek <pavel at ucw.cz> wrote:
>>
>>> Core reason is that 5ab92a7cb is wrong. (Very wrong; it papers over
>>> the issue for one trigger, but we have more than one... Even if
>>> special handling for heartbeat is warranted, that handling would be
>>> "turn the led off" not "unregister the trigger", which is
>>> userland-visible action.)
>>
>> OK yeah I guess you're right.
>>
>> I just couldn't think about anything better and didn't get any review
>> at the time, so mistakes were made.
>>
>>> That one should be reverted, then maybe the driver should be fixed
>>> to turn the led off during suspend.
>>
>> Do you mean that the heartbeat trigger driver should be fixed to turn
>> off the LED during sleep?
>>
>> That is essentially what I was trying to achieve.
>
> I don't think we should be fixing it at trigger level.
>
> If userspace keeps blinking using "brightness" attribute, would we like the LED to be off during suspend? I think so.
>
>> The reason it is done as it is, is that the trigger sets up a timer
>> to do its job, and the timer may trigger between the point you turn
>> off the LED and the system really goes to suspend, again maybe
>> turning the LED on and again leaving the system with a glowing LED at suspend.
>
>> The patch also solves the following phenomenon, sorry for not writing
>> in the commit:
>>
>> - Turn off LED
>> - Suspend I2C hardware
>> - Timer trigger
>> - Trying to blink the LED using I2C
>> - Crap in the console about the failed I2C transaction
>> - Actual suspen happens
>> - System comes online
>> - Trying to blink the LED using I2C
>> - Crap in the console about the failed I2C transaction
>> - Resume I2C hardware
>>
>> It's just very fragile this trigger, turning off the LED from the PM
>> notifier is obviously not enough, we also need to disable the timer,
>> and then take it back online after resume.
>
> No, leave the timer alone, and actually leave the trigger alone.
>
> Simply make the driver turn the LED off in .suspend() callback, and then ignore further requests until .resume(). That will get rid of power drain _and_ "failed I2C transaction" messages, right?
>
> (Actually, I tested with the heartbeat trigger, and it is not re-installed after resume. Another reason to revert the patch).
>
> Thanks,
>
> Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures)
> http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
>
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