Re: [PATCH qemu.git] target/imx: reload cmp timer outside of the reload ptimer transaction

[Peter Maydell <peter.maydell@linaro.org>]

On Mon, 24 Oct 2022 at 18:06, ~axelheider <axelheider@git.sr.ht> wrote:
>
> From: Axel Heider <axel.heider@hensoldt.net>
>
> When running seL4 tests (https://docs.sel4.systems/projects/sel4test)
> on the sabrelight platform, the timer tests fail. The arm/imx6 EPIT
> timer interrupt does not fire properly, instead of a e.g. second in
> can take up to a minute to finally see the interrupt.
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1263
>
> Signed-off-by: Axel Heider <axel.heider@hensoldt.net>
> ---
> Fixed the comment style and the commit message.
>
> > Do we also need to change the other places that call
> > imx_epit_reload_compare_timer() in the handling of CR
> > register writes ? (Those are a little more tricky.)
>
> The current patch fixed the issue we are seeing. I'm not really
> an expert on the QEMU code here and still try to understand
> all details. Might also be that we never hit the other code paths
> in the end.

I suspect your guest happens to initialize the timer in
such a way that it doesn't matter if we don't get the
comparison stuff right on the write to the control
register: conceptually I think the CR write code has the
same bug where we call imx_epit_reload_compare_timer()
before we've finalized the value of the timer_reload value.

Anyway, this patch is definitely correct for the LR
register write, so I've applied it to target-arm.next.

thanks
-- PMM