Re: [PATCH v4 0/7] Support inhibiting input devices

[Andrzej Pietrasiewicz <andrzej.p@collabora.com>]

Hi Hans,

W dniu 12.06.2020 o 10:30, Hans de Goede pisze:
> Hi,
> 
> On 6/10/20 3:41 PM, Andrzej Pietrasiewicz wrote:
>> Hi Hans,
>>
>> W dniu 10.06.2020 o 15:21, Hans de Goede pisze:
>>> Hi,
>>>
>>> On 6/10/20 3:12 PM, Andrzej Pietrasiewicz wrote:
>>>> Hi All,
>>>>
>>>> W dniu 10.06.2020 o 12:38, Rafael J. Wysocki pisze:
>>>>> On Wed, Jun 10, 2020 at 11:50 AM Hans de Goede <hdegoede@redhat.com> wrote:
>>>>>>
>>>>>> Hi All,
>>>>>>
>>>>>> On 6/8/20 1:22 PM, Andrzej Pietrasiewicz wrote:
>>>>>>> This is a quick respin of v3, with just two small changes, please see
>>>>>>> the changelog below.
>>>>>>>
>>>>>>> Userspace might want to implement a policy to temporarily disregard input
>>>>>>> from certain devices.
>>>>>>>
>>>>>>> An example use case is a convertible laptop, whose keyboard can be folded
>>>>>>> under the screen to create tablet-like experience. The user then must hold
>>>>>>> the laptop in such a way that it is difficult to avoid pressing the keyboard
>>>>>>> keys. It is therefore desirable to temporarily disregard input from the
>>>>>>> keyboard, until it is folded back. This obviously is a policy which should
>>>>>>> be kept out of the kernel, but the kernel must provide suitable means to
>>>>>>> implement such a policy.
>>>>>>
>>>>>> First of all sorry to start a somewhat new discussion about this
>>>>>> while this patch set is also somewhat far along in the review process,
>>>>>> but I believe what I discuss below needs to be taken into account.
>>>>>>
>>>>>> Yesterday I have been looking into why an Asus T101HA would not stay
>>>>>> suspended when the LID is closed. The cause is that the USB HID multi-touch
>>>>>> touchpad in the base of the device starts sending events when the screen
>>>>>> gets close to the touchpad (so when the LID is fully closed) and these
>>>>>> events are causing a wakeup from suspend. HID multi-touch devices
>>>>>> do have a way to tell them to fully stop sending events, also disabling
>>>>>> the USB remote wakeup the device is doing. The question is when to tell
>>>>>> it to not send events though ...
>>>>>>
>>>>>> So now I've been thinking about how to fix this and I believe that there
>>>>>> is some interaction between this problem and this patch-set.
>>>>>>
>>>>>> The problem I'm seeing on the T101HA is about wakeups, so the question
>>>>>> which I want to discuss is:
>>>>>>
>>>>>> 1. How does inhibiting interact with enabling /
>>>>>> disabling the device as a wakeup source ?
>>>>>>
>>>>>> 2. Since we have now made inhibiting equal open/close how does open/close
>>>>>> interact with a device being a wakeup source ?
>>>>>>
>>>>>> And my own initial (to be discussed) answers to these questions:
>>>>>>
>>>>>> 1. It seems to me that when a device is inhibited it should not be a
>>>>>> wakeup source, so where possible a input-device-driver should disable
>>>>>> a device's wakeup capabilities on suspend if inhibited
>>>>>
>>>>> If "inhibit" means "do not generate any events going forward", then
>>>>> this must also cover wakeup events, so I agree.
>>>>
>>>> I agree, too.
>>>>
>>>>>
>>>>>> 2. This one is trickier I don't think we have really clearly specified
>>>>>> any behavior here. The default behavior of most drivers seems to be
>>>>>> using something like this in their suspend callback:
>>>>>>
>>>>>>           if (device_may_wakeup(dev))
>>>>>>                   enable_irq_wake(data->irq);
>>>>>>           else if (input->users)
>>>>>>                   foo_stop_receiving_events(data);
>>>>>>
>>>>>> Since this is what most drivers seem to do I believe we should keep
>>>>>> this as is and that we should just clearly document that if the
>>>>>> input_device has users (has been opened) or not does not matter
>>>>>> for its wakeup behavior.
>>>>>>
>>>>>> Combining these 2 answers leads to this new pseudo code template
>>>>>> for an input-device's suspend method:
>>>>>>
>>>>>>          /*
>>>>>>           * If inhibited we have already disabled events and
>>>>>>           * we do NOT want to setup the device as wake source.
>>>>>>           */
>>>>>>          if (input->inhibited)
>>>>>>                  return 0;
>>>>
>>>> Right, if a device is inhibited it shouldn't become a wakeup source,
>>>> because that would contradict the purpose of being inhibited.
>>>
>>> Ack. Note I do think that we need to document this (and more
>>> in general the answer to both questions from above) clearly so
>>> that going forward if there are any questions about how this is
>>> supposed to work we can just point to the docs.
>>>
>>> Can you do a follow-up patch, or include a patch in your next
>>> version which documents this (once we agree on what "this"
>>> exactly is) ?
>>
>> Sure I can. Just need to know when "this" becomes stable enough ;)
>> If this series otherwise looks mature enough I would opt for a
>> follow-up patch.
> 
> FWIW after my flip-flop to agreeing with Dmitry that the 2
> (inhibit vs wakeup) should be completely orthogonal this new
> policy is stable/mature from my pov (and consistent with how
> we handle wakeup vs input_dev->users).
> 
> I still think it would be good to do a follow-up documentation
> patch documenting that these (and esp. inhibit) are orthogonal.
> 
> This will mean for example that if a device is inhibit but
> still wakeup enabled and the device's close method silences
> the devices, that it needs to be unsilenced in suspend.
> This might be worth mentioning in the docs even though
> drivers which silence the device on close should already
> unsilence the device on suspend when it is wakeup-enabled.
> 
> Note maybe we should give it a couple of days for others to
> give their opinion before you submit the follow-up documentation
> patch.
> 

True. I will send something after the weekend.

Andrzej