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

Andrzej Pietrasiewicz
2020-06-10T13:41:28Z

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.

>
>>>>
>>>>           if (device_may_wakeup(dev))
>>>>                   enable_irq_wake(data->irq);
>>
>> What would it mean to become a wakeup source if there are no users,
>> or nobody has ever opened the device? There are no interested
>> input handlers (users) so what's the point of becoming a wakeup
>> source? Why would the system need to wake up?
>
> Well this is what we have been doing so far, so arguably we
> need to keep doing it to avoid regressions / breaking our ABI.
>
> Lets for example take a laptop, where when suspended the
> power-button is the only valid wakeup-source and this is
> running good old slackware with fvwm2 or windowmaker as
> "desktop environment", then likely no process will have
> the power-button input evdev node open.  Still we should
> wakeup the laptop on the power-button press, otherwise
> it will never wakeup.
>

True, thanks for explaining.

> Note I agree with you that the way this works is not
> ideal, I just do not think that we can change it.
>

Regards,

Andrzej