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

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Message-ID: <CAE=W-e0utnP2RyFrK1_ex8ZDjvuA2kUm0Z6wnGjUSeXZC302pQ@mail.gmail.com>
Date:	Fri, 3 Jul 2015 13:23:24 +0200
From:	Lorenzo Nava <lorenx4@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5] arm DMA: Fix allocation from CMA for coherent DMA

On Fri, Jul 3, 2015 at 11:03 AM, Russell King - ARM Linux
<linux@....linux.org.uk> 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@...il.com>
>> > Reviewed-by: Catalin Marinas <catalin.marinas@....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?
>

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


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