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From: Michal Nazarewicz <mina86@mina86.com>
Subject: Re: CMA alignment question
In-Reply-To: <CAL1ERfMYmQcQ_sX7E0HC2bXmC-imh4T-7Q4nBVQRXkQSaTjvQQ@mail.gmail.com>
References: <CADtm3G7DtGkvPk36Fiunwen8grw-94V6=iv82iusGumfNJkn-g@mail.gmail.com> <xa1tlhnq7ga7.fsf@mina86.com> <CADtm3G7bU6Y2aKco5Vb81KSqsy=FH9zmdDJm=Tixjoep1YeJ7Q@mail.gmail.com> <CAL1ERfMYmQcQ_sX7E0HC2bXmC-imh4T-7Q4nBVQRXkQSaTjvQQ@mail.gmail.com>
Date: Wed, 05 Nov 2014 23:01:48 +0100
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Sender: owner-linux-mm@kvack.org
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To: Weijie Yang <weijie.yang.kh@gmail.com>, Gregory Fong <gregory.0xf0@gmail.com>
Cc: linux-mm@kvack.org, Laura Abbott <lauraa@codeaurora.org>, iamjoonsoo.kim@lge.com, Marek Szyprowski <m.szyprowski@samsung.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Florian Fainelli <f.fainelli@gmail.com>, Brian Norris <computersforpeace@gmail.com>

> On Tue, Nov 04 2014, Gregory Fong wrote:
>> The alignment in cma_alloc() is done w.r.t. the bitmap.  This is a
>> problem when, for example:
>>
>> - a device requires 16M (order 12) alignment
>> - the CMA region is not 16 M aligned

On Wed, Nov 05 2014, Weijie Yang wrote:
> I think the device driver should ensure that situation could not occur,
> by assign suitable alignment parameter in cma_declare_contiguous().

What about default CMA area? Besides, I think principle of least
surprise applies here and alignment should be physical.

--=20
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.o. | Liege of Serenely Enlightened Majesty of      o' \,=3D./ `o
..o | Computer Science,  Micha=C5=82 =E2=80=9Cmina86=E2=80=9D Nazarewicz   =
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