linux-kernel - Re: [PATCH] can: mcp251x: Use dmam_alloc

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Message-ID: <CAG9MbtLNoVhbFbnm25RSP02p60oF65Z-S80FhB=FVW7SrLu+Tg@mail.gmail.com>
Date:	Tue, 5 Aug 2014 13:02:52 +0200
From:	christian pellegrin <chripell@...e.org>
To:	Stefano Babic <sbabic@...x.de>
Cc:	Himangi Saraogi <himangi774@...il.com>,
	Alexander Shiyan <shc_work@...l.ru>, julia.lawall@...6.fr,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Jingoo Han <jg1.han@...sung.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] can: mcp251x: Use dmam_alloc_coherent

Hi all,

BTW the reason that use of DMA is selectable by a parameter is that on
some architectures (for example the venerable S3C24x0) the cost for
its setup is so high that it doesn't make sense for smaller transfers.
I absolutely agree with Stefano and Alexander, the SPI master driver
is in the best position to decide if DMA is worth or not.


On Tue, Aug 5, 2014 at 10:23 AM, Stefano Babic <sbabic@...x.de> wrote:
>> Just for information: On my opinion, all SPI DMA stuff should be going into SPI layer.
>> It is not a good idea to keep this into this driver.
>
> If I can add my two cents, I agree with Alexander. An underlying SPI
> (master) controller driver can or cannot support DMA transfer, and this
> should be transparent to the CAN layer. The mcp251x driver works with
> both of them, taking advantage when DMA is available.




-- 
Christian Pellegrin, see http://www.evolware.org/chri/
"Real Programmers don't play tennis, or any other sport which requires
you to change clothes. Mountain climbing is OK, and Real Programmers
wear their climbing boots to work in case a mountain should suddenly
spring up in the middle of the computer room."
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