[Letux-kernel] Timers (was Re: [PATCH 00/20] A bunch of JZ4730 fixups for letux-kernel)

[H. Nikolaus Schaller]

> Am 19.01.2021 um 10:15 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> So we have learned that sleep 10 indeed calls hrtimer_nanosleep() resp.
> do_nanosleep() and there we somehow get the factor 2 compared to what
> user-space assumes.
> 
> We are getting closer...

ok, starting a hrtimer goes down to clockevents_program_event()
This uses a struct clock_event_device which controls the real
hardware.

Do we have an idea which one we use on the jz4730?

Seems to be

https://elixir.bootlin.com/linux/v5.11-rc3/source/drivers/clocksource/ingenic-timer.c#L35

So we are back at the TCU and OST driver!

After studying the code I think I got it:

ingenic_tcu_cevt_set_next()

There, we are simply writing the next value to TCU_JZ4730_REG_TRDRc
without taking into account that it is counting backwards. IMHO it must
be the reverse operation to ingenic_tcu_timer_read() so that

ingenic_tcu_cevt_set_next(value, ...);
ingenic_tcu_timer_read();

should return almost the same value!

ingenic_tcu_cevt_set_next() is only called for the hrtimers but
not for the sched_clock() (which is freely running and overflowing).

What do you think?

BR,
Nikolaus