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

[Jacek Anaszewski]

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.

Would you mind submitting the patch so that everyone interested
could give their ack?

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
>>
> 
>