linux-kernel - Re: [PATCH 1/2] dmaengine: Fix status handling in imx-dma.

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Date:	Fri, 6 Jan 2012 13:43:11 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	dan.j.williams@...el.com,
	Javier Martin <javier.martin@...ta-silicon.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dmaengine: Fix status handling in imx-dma.

On Fri, Jan 06, 2012 at 04:40:24PM +0530, Vinod Koul wrote:
> On Fri, 2012-01-06 at 10:37 +0100, Sascha Hauer wrote:
> > On Fri, Jan 06, 2012 at 11:26:29AM +0530, Vinod Koul wrote:
> > > On Mon, 2012-01-02 at 13:18 +0100, Javier Martin wrote:
> > > > Status must only be changed to DMA_IN_PROGRESS
> > > > when the DMA transfer has really begun.
> > > > 
> > > > However, since this driver lacks of support for
> > > > multiple descriptors a new flag has to be introduced
> > > > to avoid the prepare function be called multiple times.
> > > Thanks this is the right approach to fix this driver
> > > 
> > > But this will obviously break any users of this driver as they need to
> > > call the right APIs now :D
> > > 
> > > Sacha: can you check this patch and see which users of this driver will
> > > break. we need those fixes to go along this patch as well
> > 
> > Which users should break? I just tried with the mxcmmc driver and this
> > one does not break.
> > 
> > I do not really understand this patch anyway. It changes imxdmac->status
> > to a write-only variable and introduces a imxdmac->prepared variable
> > with the same meaning. This patch is a complicated no-op.
> > 
> > What was the original problem? The fact that we used a enum dma_status
> > with the wrong semantics? In that case I suggest to simply replace this
> > variable. All we need to track is that we do not enter
> > imxdma_prep_slave_sg with an already running transfer.
> the memcpy patch submitted earlier didn't use correct dmaengine API. a
> descriptor is not supposed to be started in prepare. The reason given
> was the driver already does so for all other prepares, so i suggested to
> fix that. Descriptors should be started in issue_pending only.

The transfer is not started in prepare but in imxdmac->desc.tx_submit

Sascha


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