linux-kernel - Re: [PATCH v2 1/5] drivers: of: add initialization code for reserved memory

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Message-ID: <52FA87B8.8040203@gmail.com>
Date:	Tue, 11 Feb 2014 21:27:36 +0100
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Josh Cartwright <joshc@...eaurora.org>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Grant Likely <grant.likely@...aro.org>,
	Tomasz Figa <t.figa@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-mm-sig@...ts.linaro.org, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Arnd Bergmann <arnd@...db.de>,
	Michal Nazarewicz <mina86@...a86.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Laura Abbott <lauraa@...eaurora.org>,
	Rob Herring <robh+dt@...il.com>,
	Olof Johansson <olof@...om.net>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Kumar Gala <galak@...eaurora.org>,
	Nishanth Peethambaran <nishanth.p@...il.com>,
	Marc <marc.ceeeee@...il.com>
Subject: Re: [PATCH v2 1/5] drivers: of: add initialization code for reserved
 memory



On 11.02.2014 21:19, Josh Cartwright wrote:
> On Tue, Feb 11, 2014 at 09:04:21PM +0100, Tomasz Figa wrote:
>>
>>
>> On 11.02.2014 21:02, Benjamin Herrenschmidt wrote:
>>> On Tue, 2014-02-11 at 19:01 +0000, Grant Likely wrote:
>>>
>>>>> except that the former IMHO better suits the definition of memory
>>>>> region, which I see as a single contiguous range of memory and can be
>>>>> simplified to have a single reg entry per region.
>>>>
>>>> My point is rather if multiple reg tuples are found in a reserved memory
>>>> node, the kernel must respect them and reserve the memory. I'm not
>>>> arguing about whether or not that makes for a good binding.
>>>
>>> agreed.
>>
>> My point is why, if the binding defines that just a single tuple should be
>> provided.
>
> FWIW, the usecase I had mentioned in reply to Grant in the patch 5/5
> thread [1] could make use of this.  The shared memory region is split
> into a main chunk and several "auxiliary" chunk, but collectively these
> regions all share the same heap state.
>
>    Josh
>
> 1: http://lkml.kernel.org/r/20140205192502.GO20228@joshc.qualcomm.com
>

The use case seems fine, but I believe it could be properly represented 
in device tree using multiple single-reg regions as well, unless the 
consumer can request a block of memory that crosses boundary of two 
sub-regions specified by reg entries of single region.

Best regards,
Tomasz
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