From mboxrd@z Thu Jan  1 00:00:00 1970
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
Subject: Re: [PATCH V2 6/6] spi/spi-pl022: Request/free DMA channels as and
	when required.
Date: Wed, 10 Aug 2011 11:32:25 +0100
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Cc: Pratyush ANAND <pratyush.anand@st.com>,
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	Bhupesh SHARMA <bhupesh.sharma@st.com>,
	Shiraz HASHIM <shiraz.hashim@st.com>, "Koul, Vinod" <vinod.koul@intel.com>,
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	Vipin KUMAR <vipin.kumar@st.com>,
	Armando VISCONTI <armando.visconti@st.com>, Amit VIRDI <Amit.VIRDI@st.com>,
	Vipul Kumar SAMAR <vipulkumar.samar@st.com>,
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	Deepak SIKRI <deepak.sikri@st.com>,
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	<spi-devel-general@lists.sourceforge.net>, "Williams,
	Dan J" <dan.j.williams@intel.com>, "linux-arm-kernel@lists.infradead.org"
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To: viresh kumar <viresh.kumar@st.com>
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On Wed, Aug 10, 2011 at 03:44:13PM +0530, viresh kumar wrote:
> On 08/10/2011 03:31 PM, Koul, Vinod wrote:
> > And on your patch, are you able to dynamically assign the channels for
> > platform? What is the intended usage? (as Russell articulated it is bad
> > to dynamically assign channel for something like uart)
> 
> Are you talking about channels or DMA request lines? For channels yes,
> we can always allocate channels as they are independent of peripherals.
> About request lines, they are muxed in our case between several
> peripherals, but support for that has to be added in dw_dmac.

Right, and when you do, you'll probably have to go to a virtual channel
implementation, which solves the problem of keeping a channel allocated
and makes this patch redundant.

I assert that any DMA engine implementation where request signals can
be assigned dynamically to DMA channels should be using a virtual channel
implementation.