Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Isget_user_pages() enough to prevent pages from being swapped out ?")

From: Hugh Dickins
Date: Tue Sep 01 2009 - 12:54:34 EST

On Tue, 1 Sep 2009, Russell King - ARM Linux wrote:
> On Tue, Sep 01, 2009 at 03:43:48PM +0200, Laurent Pinchart wrote:
> > I might be missing something obvious, but I fail to see how VIVT caches
> > could work at all with multiple mappings. If a kernel-allocated buffer
> > is DMA'ed to, we certainly want to invalidate all cache lines that store
> > buffer data. As the cache doesn't care about physical addresses we thus
> > need to invalidate all virtual mappings for the buffer. If the buffer is
> > mmap'ed in userspace I don't see how that would be done.
> You need to ask MM gurus about that. I don't touch the Linux MM very
> often so tend to keep forgetting how it works. However, it does work
> for shared mappings of files on CPUs with VIVT caches.

I believe arch/arm/mm/flush.c __flush_dcache_aliases() is what does it.

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