linux-kernel - Re: [PATCHv2] DMAEngine: Let dmac drivers to set chan

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Date:	Wed, 27 Jul 2011 15:04:24 +0530
From:	"Koul, Vinod" <vinod.koul@...el.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Jaswinder Singh <jaswinder.singh@...aro.org>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-kernel@...r.kernel.org, rmk+kernel@....linux.org.uk,
	linus.walleij@...ricsson.com, per.friden@...ricsson.com,
	wei.zhang@...escale.com, ebony.zhu@...escale.com,
	iws@...o.caltech.edu, s.hauer@...gutronix.de,
	maciej.sosnowski@...el.com, saeed@...vell.com,
	shawn.guo@...escale.com, yur@...raft.com, agust@...x.de,
	iwamatsu.nobuhiro@...esas.com, per.forlin@...ricsson.com,
	jonas.aberg@...ricsson.com, anemo@....ocn.ne.jp
Subject: Re: [PATCHv2] DMAEngine: Let dmac drivers to set chan_id

On Wed, 2011-07-27 at 12:59 +0300, Mika Westerberg wrote:
> On Wed, Jul 27, 2011 at 02:32:26PM +0530, Koul, Vinod wrote:
> > Can you please help me understand why channel number "x" is important
> > and strictly needed by some client?
> 
> At least in ep93xx we have even channel numbers for TX and odd for RX (or
> vice versa, can't rememeber). This is a hardware restriction. So the client
> code then filters the channels based on that using ->chan_id.
> 
> As the caps are not per channel, that is the only way I was able to make it
> work.
Thanks, 
Is this a dma controller limitation or due to the fact even channels get
assigned h/w interface corresponding to TX and so on.

At least on dw synopsis controllers all channels are same and you need
to assign the respective h/w interface of the port (rx and tx) you are
transferring to. If we pass and configure this in driver then client
would just need channel with capabilities and not specific number.

I am not sure if this is true for other type of controllers...

-- 
~Vinod

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