linux-kernel - Re: CMA alignment question

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Message-ID: <xa1tsihxwblf.fsf@mina86.com>
Date:	Wed, 05 Nov 2014 23:01:48 +0100
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Weijie Yang <weijie.yang.kh@...il.com>,
	Gregory Fong <gregory.0xf0@...il.com>
Cc:	linux-mm@...ck.org, Laura Abbott <lauraa@...eaurora.org>,
	iamjoonsoo.kim@....com,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Brian Norris <computersforpeace@...il.com>
Subject: Re: CMA alignment question

> 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.

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