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

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Message-ID: <Pine.LNX.4.64.1203191436030.11516@axis700.grange>
Date:	Mon, 19 Mar 2012 14:38:27 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Vinod Koul <vinod.koul@...el.com>
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, 19 Mar 2012, Vinod Koul wrote:

> 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

How?

	dma_request_channel(mask, filter_fn, filter_arg)

Where shall the client pass to dmaengine its identity info?

> 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.

Some clients need multiple channels - Tx, Rx,...

Thanks
Guennadi

> 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
> 

---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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