[[PATCH v2]] drivers: leds/trigger: system cannot enter suspend

[Jacek Anaszewski]

On 06/09/2017 10:47 PM, Jacek Anaszewski wrote:
> Hi Bruce,
> 
> On 06/09/2017 04:57 AM, Bruce Zhang wrote:
>> 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.
> 
> Indeed, it would be even harmful with the current sequence of
> instructions in the led_classdev_suspend().
> 
> So, the only action to take is to revert the commit 5ab92a7cb8.

Ugh, of course it would fix your problem with uevent, but it would
also bring back the problem the commit 5ab92a7cb8 was solving.

The question is why the problem existed at all, despite that
led_classdev_suspend() seems to do what's needed.

There are three options:
- races between led_heartbeat_function and LED core
- the LED class driver for which the phenomenon was observed
  doesn't set LED_CORE_SUSPENDRESUME flag
- if the driver uses brightness_set_blocking op, then maybe
  it is possible that the work queue task scheduled from
  led_classdev_suspend() that sets brightness to 0 isn't handled
  before the device enters suspend

We could narrow down the possible options if we knew the name of the
LED class driver in question.

Best regards,
Jacek Anaszewski


>> -----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
>>>
>>
>>