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Re: MPC8260 cache patch
On Sun, 2003-03-30 at 14:52, Jonathan Larmour wrote:
> Gary Thomas wrote:
> >
> > Technically, this should not matter. The only time this would make any
> > difference would be if the FLASH functions modified data that was already
> > within the data cache. If the lines were left valid and then the cache
> > disabled, when the cache was re-enabled, the lines in the cache could
> > override the changes in memory, leading to an inconsistent state. So,
> > for safety's sake, we should leave the invalidate calls in there. BTW,
> > as far as I can see the only time this could cause a problem would be
> > on the "inquire" function - the one that computes the size and shape of
> > the FLASH. If that data were already in the cache, then things could
> > go awry. The only other routines only write to the FLASH and should not
> > be touching memory anyway.
>
> I think this only applies to the simplest of operations. It only takes a
> read/write/read operation to risk problems. You could provoke this by
> just cksumming an area of flash before doing a write to it, and then
> cksumming it again, for example[1]. Unlikely, but, users given a CLI can
> do whatever they want :-).
>
Of course - it's easy to imagine scenarios which lead to invalid data.
As I said, the safest course is to leave the invalidates in place. That
way, when the cache comes back on, there are no assumptions about what's
in it.
> More troublesome would be flash file systems of course, and they rely on
> the underlying drivers doing the right thing.
>
> Jifl
> [1] Talking of which, I'm I the only one still showing a mismatch between
> RedBoot cksum and Linux cksum? I thought all these issues were worked out
> not all that long ago.
Is this something that you've reported [or complained about]? It always
seemed to work correctly for me.
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Gary Thomas |
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