linux-kernel - Re: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request

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Date:	Thu, 08 Mar 2012 16:25:28 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org,
	'Jassi Brar' <jassisinghbrar@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [PATCH/RFC] dmaengine: add a slave parameter to
 __dma_request_channel()

On Thu, 2012-03-08 at 11:16 +0100, Guennadi Liakhovetski wrote:
> I still have the impression, that my specific use-case (sh-mobile), where 
> channels can be freely configured for use by _ANY_ client on one of 
> _SEVERAL_ DMAC instances, is not fully understood or taken into account. 
> For this driver any kind of fixed mapping means, that we'd have to use 
> both virtual channels and controllers, adding _a lot_ of complexity to the 
> DMAC driver and making the dmaengine core just an "obfuscation layer." 
> Yes, I remember Russell proposing core helpers for this. They would help, 
> but (1) when would they be available, (2) how well would they be suitable 
> for us, (3) they'd take the coding / maintainance burden away, but 
> wouldn't reduce complexity and run-time overhead. 
Lets try to address you case as well.
On a typical platform
1) how many dma controllers you have?
2) how many clients you have
3) which client can use what controller channel? How is mapping decided,
do you have a mux, is it hard wired by soc designers,....?

Can you pls give a description so that we ensure all models fit in the
final solution?

-- 
~Vinod

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