Re: USB mass storage and ARM cache coherency

[Oliver Neukum]

Am Mittwoch, 24. Februar 2010 03:48:09 schrieb Benjamin Herrenschmidt:
> On Fri, 2010-02-19 at 21:53 +0100, Oliver Neukum wrote:
> > Am Freitag, 19. Februar 2010 18:36:51 schrieb Catalin Marinas:
> > > If a page is already mapped in user space, flush_dcache_page() on ARM
> > > does the flushing rather than deferring it to update_mmu_cache(). The
> > > PIO HCD drivers, however, don't call flush_dcache_page(). Is it possible
> > > that the HCD could transfer data into a page cache page already mapped
> > > in user space? My understanding is that the scenario above is possible.
> > 
> > Yes, video drivers do that. 
> 
> In which case it would be up to the video driver to call
> flush_dcache_page() (though if it's v4l you are talking about, maybe it
> might make sense to push it into the v4l layer itself).

I don't know. The issue seems quite complex. It would seem better to
centralize it as far as practical. Do you have a wrapper drivers could
call?

	Regards
		Oliver
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