Re: [PATCHv2 0/7] Support inhibiting input devices

Hans de Goede
2020-05-18T12:24:12Z

Hi,

On 5/18/20 12:48 PM, Andrzej Pietrasiewicz wrote:
> Hi Hans,
>
> W dniu 15.05.2020 o 20:19, Hans de Goede pisze:
>> Hi Andrezj,
>>
>> On 5/15/20 6:49 PM, Andrzej Pietrasiewicz wrote:
>>> Userspace might want to implement a policy to temporarily disregard input
>>> from certain devices, including not treating them as wakeup sources.
>>>
>>> An example use case is a 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.
>>
>> Actually libinput already binds together (inside libinput) SW_TABLET_MODE
>> generating evdev nodes and e.g. internal keyboards on devices with 360°
>> hinges for this reason. libinput simply closes the /dev/input/event#
>> node when folded and re-opens it when the keyboard should become active
>> again. Thus not only suppresses events but allows e.g. touchpads to
>> enter runtime suspend mode which saves power. Typically closing the
>> /dev/input/event# node will also disable the device as wakeup source.
>>
>> So I wonder what this series actually adds for functionality for
>> userspace which can not already be achieved this way?
>>
>> I also noticed that you keep the device open (do not call the
>> input_device's close callback) when inhibited and just throw away
>
> I'm not sure if I understand you correctly, it is called:
>
> +static inline void input_stop(struct input_dev *dev)
> +{
> +    if (dev->poller)
> +        input_dev_poller_stop(dev->poller);
> +    if (dev->close)
> +        dev->close(dev);
>                 ^^^^^^^^^^^^^^^^
> +static int input_inhibit(struct input_dev *dev)
> +{
> +    int ret = 0;
> +
> +    mutex_lock(&dev->mutex);
> +
> +    if (dev->inhibited)
> +        goto out;
> +
> +    if (dev->users) {
> +        if (dev->inhibit) {
> +            ret = dev->inhibit(dev);
> +            if (ret)
> +                goto out;
> +        }
> +        input_stop(dev);
>                 ^^^^^^^^^^^^^^^^
>
> It will not be called when dev->users is zero, but if it is zero,
> then nobody has opened the device yet so there is nothing to close.

Ah, I missed that.

So if the device implements the inhibit call back then on
inhibit it will get both the inhibit and close callback called?

And what happens if the last user goes away and the device
is not inhibited?

I'm trying to understand here what the difference between the 2
is / what the goal of having a separate inhibit callback ?

IOW is there something which we want to do on close when
the close is being done to inhibit the device, which we do
not want to do on a normal close ?

Regards,

Hans