[PATCH v5] arm DMA: Fix allocation from CMA for coherent DMA

Russell King - ARM Linux linux at arm.linux.org.uk
Fri Jul 3 02:03:06 PDT 2015

On Wed, Jul 01, 2015 at 12:12:51PM +0100, Catalin Marinas wrote:
> On Tue, Jun 30, 2015 at 11:29:06PM +0200, Lorenzo Nava wrote:
> > This patch allows the use of CMA for DMA coherent memory allocation.
> > At the moment if the input parameter "is_coherent" is set to true
> > the allocation is not made using the CMA, which I think is not the
> > desired behaviour.
> > 
> > Signed-off-by: Lorenzo Nava <lorenx4 at gmail.com>
> > Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
> If Russell doesn't have any objections, you can send the patch to
> his patch system. See here for more information:

I'm left wondering whether this patch is really want Lorenzo wants.
>From my reading of it, while this has the effect of allocating from
CMA for coherent devices, it's no different from the non-coherent
case, because by calling __alloc_from_contiguous(), we end up
remapping the allocated memory, removing the cacheability status
from the allocated pages.

This brings up an interesting point: presumably, it's been tested, and
people are happy with the performance it's giving, inspite of it not
returning cacheable memory... or maybe it hasn't been tested that much?

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