Is delayed work's precision good enough for input-poller?

[Nicolas Saenz Julienne <nsaenzjulienne@suse.de>]

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Hi everyone,
I just found about an issue in the downstream Raspberry Pi[1] kernel that I
wonder if it'd be worth fixing generally. The official RPi DSI display
touchscreen uses the polled input interface. The ts chip works at around 60Hz,
and that's the period the driver is configured to use (17ms). This doesn't play
too good on systems with low HZ (100/250). Users complain that in practice they
experience, at worst, half the event rate. This is due to the rounding error
when converting milliseconds to jiffies, general system delays, and what not.

We could somewhat fix this in the driver (raspberrypi-ts.c) by playing with the
poll rate. But it seems pretty hacky and would ultimately stress the CPU
unnecessarily. I wonder to what extent it makes sense to move the
implementation to using hrtimers whenever the poll period is in the same order
of magnitude as HZ's delta.

Any ideas/comments?

Regards,
Nicolas

[1] https://github.com/raspberrypi/linux/issues/3777#issuecomment-698346991


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