[PATCH] powerpc: reduce number of WATCHDOG_RESET calls from flush_cache

[Tom Rini]

On Wed, Sep 23, 2020 at 02:48:18PM +0200, Wolfgang Denk wrote:
> Dear Rasmus,
> 
> In message <afea5640-9d95-bf92-316a-0d674a5129ce at prevas.dk> you wrote:
> > On 04/06/2020 12.31, Stefan Roese wrote:
> > > On 04.06.20 11:30, Rasmus Villemoes wrote:
> > >> Calling WATCHDOG_RESET for each and every cache line is overkill.
> > >>
> > >> In our case, the kernel image is a little over 7MB, and the almost
> > >> 500000 calls of WATCHDOG_RESET() adds about one second to the
> > >> boottime.
> > >>
> > >> I very highly doubt there's any real hardware where flushing 64K
> > >> from cache to memory takes more than a few milliseconds, so this
> > >> should be completely safe. Since it reduces the number of
> 
> Maybe it is, maybe it is not.  I remember boards where the watchdog
> trigger had to happen in pretty tight intervals, something like min
> 20, max 60 milliseconds.
> 
> > >> +        if ((addr & (SZ_64K - 1)) == 0)
> 
> In any case, please write readable code.  The use of SZ_ here is not
> a good idea.  Also, you might want to make the actual parameter
> configurable, so boards with specific timing requirements can adjust
> this as needed.

We should add a comment somewhere here to match the commit message, but
since we're flushing on 64K chunks, SZ_64K makes sense.  If we make it
build-time configurable then it's not a concern.  I assume we don't want
to make this run time configurable.

-- 
Tom
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