We want to be able to report the input event as soon as the debounce
delay elapsed. However, the current code does not really ensure that,
as it uses the jiffies-based schedule_delayed_work() API. With a small
enough HZ value (HZ <= 100), this results in some input events being
lost, when a key is quickly pressed then released (on a human's time
scale).

Switching to hrtimers fixes this issue, and will work even on extremely
low HZ values (tested at HZ=24). This is however only possible if
reading the GPIO is possible without sleeping. If this condition is not
met, the previous approach of using a jiffies-based timer is taken.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20210307222240.380583-3-paul@crapouillou.netSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>