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

[Lorenzo Nava]

On Fri, Jul 3, 2015 at 11:03 AM, Russell King - ARM Linux
<linux@xxxxxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxx>
>> > Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
>>
>> 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?
>

As Catalin correctly pointed out, I always consider that this patch:

https://lkml.org/lkml/2015/5/7/512

has been applied. The memory returned by mmap is then cacheable and
preserve the attributes used during allocation.
Of course, without that patch, mine is not working at all.

(Sorry for the previous mail which has been sent accidentally).

Lorenzo
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