linux-kernel - Re: [PATCH 0/4] Fix the left DMA_NONE from dma_transfer

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Message-ID: <20111220125401.GA5129@S2101-09.ap.freescale.net>
Date:	Tue, 20 Dec 2011 20:54:02 +0800
From:	Shawn Guo <shawn.guo@...escale.com>
To:	Vinod Koul <vinod.koul@...el.com>
CC:	Shawn Guo <shawn.guo@...aro.org>, Chris Ball <cjb@...top.org>,
	Artem Bityutskiy <artem.bityutskiy@...el.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Huang Shijie <b32955@...escale.com>,
	<linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH 0/4] Fix the left DMA_NONE from dma_transfer_direction
 migration

On Tue, Dec 20, 2011 at 02:54:04PM +0530, Vinod Koul wrote:
> On Tue, 2011-12-13 at 23:48 +0800, Shawn Guo wrote:
> > I have been working on -rc recently, and have not noticed the failure
> > until I ran next tree today.  The mxs-mmc driver is broken on next
> > tree because the DMA_NONE was left over from the dma_transfer_direction
> > migration for mxs-dma and its client drivers.
> > 
> For DMA transfer, the NONE direction makes no sense?
> 
> In your conetext, what are you trying to achieve?
> 
The mxs-dma controller has a feature to program peripheral registers
with given values (mxs-dma PIO mode).  This is designed to pipeline
the operations.  For example, we can put mxs-mmc controller register
values into scatter list as one element together with actual data.
Triggering the mxs-dma, the dma will program the values into mxs-mmc
controller register to set up and enable mxs-mmc, and then dma
continue transfer data from/to mxs-mmc.  All these get done in one
dmaengine_submit().

And DMA_NONE was used to let mxs-dma know this is a PIO operation.

-- 
Regards,
Shawn

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