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

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Message-ID: <Pine.LNX.4.64.1203091022200.7852@axis700.grange>
Date:	Fri, 9 Mar 2012 10:24:29 +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 Fri, 9 Mar 2012, Vinod Koul wrote:

> On Thu, 2012-03-08 at 14:18 +0100, Guennadi Liakhovetski wrote:
> > > Assuming I didn't miss...
> > > 
> > > The case B can be handled without sweat by platforms channel mapping
> > > information.
> > > 
> > > Case A where we don't find that devices exist in map, thus being treated
> > > as generic DMA channels and can be handled easily in sequence. So when
> > > someone in Q request a channel it would get first channel in Ps
> > > 
> > > This way we handle both of them in a transparent manner to both clients
> > > and controllers. 
> > > 
> > > Perhaps we can also add capability to know that if channel is to be
> > > searched in map or not - would be anyway required for non slave cases.
> > 
> > Right, but I don't understand then what this gives us. You propose some 
> > channel maps, that will not be used for your "case A." Which means, for 
> > "case A" nothing changes. So, the reason for this whole thread hasn't been 
> > addressed: how to pass channel configuration to the DMA controller driver.
> For "Case A" there should be no filtering or any issues even now. You
> have controller requesting a channel and as long as they get a channel
> for respective pool, it should work.
> 
> Or is there anything else which is required in this case?

Yes, there is. You keep complaining about my use of .priv pointer, which I 
use in the filter to pass channel configuration to the DMA controller 
driver. That is the original reason for this whole discussion. If you're 
fine with that, I'll just carry that .priv use over in the "simple" DMA 
engine driver and stay happy forever:-)

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