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

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Message-ID: <CACRpkdZ+B1Joo7HgRnT4Eay0JEzkr105tgnON+J5YQLHsqm6jw@mail.gmail.com>
Date:	Wed, 7 Mar 2012 17:20:00 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Vinod Koul <vinod.koul@...el.com>,
	linux-kernel@...r.kernel.org,
	Jassi Brar <jassisinghbrar@...il.com>,
	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 Wed, Mar 7, 2012 at 11:31 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:

> For example, the SA11x0 IrDA driver uses two virtual channels, one for
> receive and one for transmit.  The SA11x0 has a total of five DMA
> channels.  To waste two of them on IrDA when it's half-duplex is just
> silly.  Doing the whole 'request+free' thing is also silly because
> switching between tx and rx mode is timing-critical.

Oh. that's luxury! The ARM PB11MPcore has two physical DMA
channels.

If I lock one up for say continous UART RX I have only one left,
and that need to do everything else. So multiplexing the physical
engines it is a must.

Yours,
Linus Walleij
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