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SubjectRe: [RFC PATCH v2 07/14] m68k: atari: Convert to clocksource API
On Sat, 24 Nov 2018, Michael Schmitz wrote:

>
> Am 20.11.2018 um 23:02 schrieb Andreas Schwab:
> > On Nov 20 2018, Linus Walleij <linus.walleij@linaro.org> wrote:
> >
> > > Yes you already see the same as I see: this chip MK68901 has no less
> > > than four timers. I bet the kernel is just using one of them, out of
> > > habit.
> >
> > Note that not all timers can be used freely. Some of them are
> > hardwired to generate the clock for the serial interfaces.
>
> Timer A is used by the DMA sound driver - no workaround possible there.
>
> Timer B is used by the framebuffer driver, but it's used only once to
> reprogram the screen base address at driver init. This one could
> potentially be used after framebuffer init to improve the clocksource
> accuracy.
>

I don't think it would make a good clocksource as MFP timers are all 8
bits wide. It could be used as a clock event device in the course of a
GENERIC_CLOCKEVENTS conversion (discussed elsewhere in this thread),
though the longest timed interrupt inverval would be only 21 ms.

--

> Timer D is already used to generate timer interrupts used to poll the
> ROM port network card / USB adapters. This timer is initialized early in
> the boot process, which prevents using the MFP UART as serial console
> (something that I hadn't properly considered before). I'll send a patch
> for that. I'll also consider using timer B or timer C interrupts instead
> to poll ROM port hardware.
>
> There are no serial drivers anymore that could use the MFP UART
> hardware, so that point is somewhat moot at present.
>
> Cheers,
>
> Michael
>
> > Andreas.
> >
>

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