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

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Date:	Mon, 19 Mar 2012 19:04:22 +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 Mon, 2012-03-19 at 12:47 +0100, Guennadi Liakhovetski wrote:
> As I wrote in a reply to Linus W - you need to pass information about the 
> requesting client to the dmaengine core to let it match it against mapping 
> tables. 
NO. 
The client only needs to say that he needs a channel for DMA_SLAVE
DMAengine will know for this client, the platform channel map (already
given to it by platform) says that we can give it DMAC X, channel 4
only. So see if it free, if so allocate it and give to client (while
doing usual stuff)
> You have to pass this information with the dma_request_channel() 
> function. So, either you need to add a parameter or you have to reuse one 
> of existing ones, e.g., deprecate the filter and use its argument for this 
> purpose. If you do this and as long as you pass that parameter further on 
> to the dmaengine device (controller) driver after whatever matching you 
> like to do in the core - I'm fine with that, that fits well with my 
> initial proposal.
I don't care about filter, it can go away if it is not required.

Passing slave_config is *enhancement* so for (hopefully) last time
 a) it has *nothing* to do with getting a channel, no role to play in
generic scheme of things
 b) it allows client to call one api for get+configure thats all! 

-- 
~Vinod

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