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

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Message-ID: <20110727095909.GB16623@intel.com>
Date:	Wed, 27 Jul 2011 12:59:09 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	"Koul, Vinod" <vinod.koul@...el.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, 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.
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