Re: [RFC] ARM DMA mapping TODO, v1

[Benjamin Herrenschmidt]

On Wed, 2011-04-27 at 10:52 +0100, Catalin Marinas wrote:
> 
> It's not broken since we moved to using Normal non-cacheable memory
> for the coherent DMA buffers (as long as you flush the cacheable alias
> before using the buffer, as we already do). The ARM ARM currently says
> unpredictable for such situations but this is being clarified in
> future updates and the Normal non-cacheable vs cacheable aliases can
> be used (given correct cache maintenance before using the buffer).

Don't you have a risk where speculative loads or prefetches might bring
back some stuff into the cache via the cachable mapping ? Is that an
issue ? As long as it's non-dirty and the cachable mapping isn't
otherwise used, I suppose it might be a non-issue, tho I've seen in
powerpc land cases of processors that can checkstop if a subsequent non
cachable access "hits" the stuff that was loaded in the cache.

Cheers,
Ben.


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