On Fri, Feb 2, 2018 at 3:52 PM, Jacek Anaszewski
<jacek.anaszewski@xxxxxxxxx> wrote:
> On 02/02/2018 04:40 PM, Samuel Morris wrote:
>> On Thu, Feb 1, 2018 at 4:29 PM, Jacek Anaszewski
>> <jacek.anaszewski@xxxxxxxxx> wrote:
>>> Hi Samuel,
>>>
>>> Thanks for the patch.
>>>
>>> On 01/30/2018 03:55 PM, Samuel Morris wrote:
>>>> On Tue, Jan 30, 2018 at 3:28 AM, Pavel Machek <pavel@xxxxxx> wrote:
>>>>> On Mon 2018-01-29 19:49:47, 0v3rdr0n3@xxxxxxxxx wrote:
>>>>>> From: Samuel Morris <samorris@xxxxxxxxxxx>
>>>>>>
>>>>>> Signed-off-by: Samuel Morris <samorris@xxxxxxxxxxx>
>>>>>
>>>>> But... we'll really need description what this is supposed to do.
>>>>
>>>> I have an LED that indicates to the user that the machine is still
>>>> powered when in suspend, so it needs to remain powered. This LED uses
>>>> the leds-pwm driver, but it may use a different driver on future
>>>> products, so making this change in that driver only would not be
>>>> ideal. I asked linux-pm a related question a week or two ago, and
>>>> Raphael Wysocki suggested looking into the PM_QOS_FLAG_NO_POWER_OFF
>>>> flag. This is what I came up with. I realize this is a pretty broad
>>>> change, but I figured I'd try the most general thing first.
>>>>
>>>>>
>>>>> Because at least some LEDs (keyboard LEDs on PC) can't be powered on
>>>>> during suspend.
>>>>
>>>> That is why I set the default behavior to PM_QOS_FLAG_NO_POWER_OFF=0 on probe.
>>>>
>>>>>
>>>>> Does this work for your LEDs? Do we need a way for userspace to tell
>>>>> if LED supports it or not?
>>>>
>>>> Yes, this fixes my problem. I could try testing on other LEDs as well
>>>> that use different drivers if need be.
>>>>
>>>> I didn't see any reason not to make this userspace configurable. I
>>>> imagine for some LEDs, the switch just won't work. Are you aware of
>>>> any cases where attempting to keep an LED on would cause outright
>>>> breakage? I would like these QoS parameters to be device tree, or
>>>> otherwise per-board configurable, but I'm not aware of a standard way
>>>> to do that. Maybe someone from linux-pm has an idea. Something like
>>>> that might be more reasonable than allowing default userspace
>>>> configurability.
>>>
>>> There is already retain-state-suspended property defined in
>>> Documentation/devicetree/bindings/leds/leds-gpio.txt and used
>>> in drivers/leds/leds-gpio.c. Now if we are going to add generic
>>> pm_qos support to the LED core, the DT property should be made generic
>>> too and moved to the Documentation/devicetree/bindings/leds/common.txt.
>>
>> Sounds good, I'll start working on it. Though I can't help but think,
>> if all devices share this pm_qos interface, couldn't the device tree
>> interface be shared as well?
>
> Could you please elaborate on that?
It just seems odd to me that there does not seem to be a standard way
to set QoS parameters like PM_QOS_FLAG_NO_POWER_OFF from the device
tree. Each subsystem must define its own way of saying essentially the
same thing afaik: leds-gpio chose 'retain-state-suspended' but it
could be any variation on "don't power off this device in suspend".
>
>>> Then, if the property is present, we shouldn't expose this setting
>>> to the userspace, see below.
>>
>> I'm okay with dt only configurability. Though, if you're suggesting we
>> should expose the flag to userspace based on whether or not it's dt
>> configurable, I'm not so sure. I think those decisions should be
>> independent.
>
> My concern here is backward compatibility - current users expect that
> once the property is set in DT, the behavior on suspend is guaranteed
> to not change.
I see now, yes, in a later patch, if we do expose this to userspace,
it would only initialize to zero if there is no dt setting.
>
>> When you expose that flag with dev_pm_qos_expose_flags(),
>> you also expose other flags.
>
> How so? You're exposing only one flag:
>
> dev_pm_qos_expose_flags(led_cdev->dev, PM_QOS_FLAG_NO_POWER_OFF)
Oh, yes, you're right, I don't know what I was thinking...
>
> I'm not familiar with this interface, though.
>
>> I will probably just remove the userspace
>> configurability for now. That can go in a separate patch, and maybe
>> that can be configurable from the dt, or a kernel config parameter.
>
> I'm fine with that.
>
>>>>>
>>>>>> @@ -196,6 +197,11 @@ static int led_suspend(struct device *dev)
>>>>>> {
>>>>>> struct led_classdev *led_cdev = dev_get_drvdata(dev);
>>>>>>
>>>>>> + if(dev_pm_qos_flags(dev, PM_QOS_FLAG_NO_POWER_OFF) ==
>>>>>> + PM_QOS_FLAGS_ALL) {
>>>>>> + return 0;
>>>>>> + }
>>>>>
>>>>> "if (". No need for { } s.
>>>>
>>>> Ok, I'll generate a new patch later if this seems likely to be integrated.
>>>
>>> Please also address problems detected by build bot [0].
>>
>> Will do.
>>
>>>
>>>>>> +
>>>>>> if (led_cdev->flags & LED_CORE_SUSPENDRESUME)
>>>>>> led_classdev_suspend(led_cdev);
>>>>>>
>>>>>> @@ -206,6 +212,11 @@ static int led_resume(struct device *dev)
>>>>>> {
>>>>>> struct led_classdev *led_cdev = dev_get_drvdata(dev);
>>>>>>
>>>>>> + if(dev_pm_qos_flags(dev, PM_QOS_FLAG_NO_POWER_OFF) ==
>>>>>> + PM_QOS_FLAGS_ALL) {
>>>>>> + return 0;
>>>>>> + }
>>>>>> +
>>>>>> if (led_cdev->flags & LED_CORE_SUSPENDRESUME)
>>>>>> led_classdev_resume(led_cdev);
>>>>>>
>>>>>> @@ -287,6 +298,18 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
>>>>>> list_add_tail(&led_cdev->node, &leds_list);
>>>>>> up_write(&leds_list_lock);
>>>>>>
>>>>>> + /* Attempt to let userspace take over the policy. */
>>>>>> + ret = dev_pm_qos_expose_flags(led_cdev->dev,
>>>>>> + PM_QOS_FLAG_NO_POWER_OFF);
>>>>>> + if (ret < 0) {
>>>>>> + dev_warn(led_cdev->dev, "failed to expose pm_qos_no_poweroff\n");
>>>>>> + return 0;
>>>>>> + }
>>>>>> +
>>>>>> + ret = dev_pm_qos_update_flags(led_cdev->dev,
>>>>>> + PM_QOS_FLAG_NO_POWER_OFF,
>>>>>> + 0);
>>>>>> +
>>>
>>> So this part should be executed conditionally only if
>>> retain-state-suspended wasn't defined. BTW you will have
>>> to rebase your code onto some more recent code base.
>>>
>>> led_classdev_register() was renamed to of_led_classdev_register()
>>> in 4.12 and it now accepts struct device_node. leds-gpio.c was
>>> already changed to use it so it will be convenient to test the use case
>>> with retain-state-suspended DT property.
>>
>> Sounds good.
>>
>>>
>>>>>> if (!led_cdev->max_brightness)
>>>>>> led_cdev->max_brightness = LED_FULL;
>>>>>
>>>>> Best regards,
>>>>> Pavel
>>>>> --
>>>>> (english) http://www.livejournal.com/~pavelmachek
>>>>> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
>>>>
>>>> thanks,
>>>> Sam
>>>>
>>>
>>> [0] https://www.spinics.net/lists/linux-leds/msg09031.html
>>>
>>> --
>>> Best regards,
>>> Jacek Anaszewski
>>
>> Thanks for the feedback,
>> Sam
>>
>
> --
> Best regards,
> Jacek Anaszewski
thanks,
Sam
