linux-kernel - Re: [PATCH 2/2] dma: mv_xor: do not sync the DMA buffer after being deallocated

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Date:	Sun, 13 Jan 2013 14:18:57 +0100
From:	Lubomir Rintel <lkundrak@...sk>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	Dan Williams <djbw@...com>, Vinod Koul <vinod.koul@...el.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] dma: mv_xor: do not sync the DMA buffer after
 being deallocated

On Fri, 2013-01-04 at 17:10 +0100, Thomas Petazzoni wrote:
> Dear Lubomir Rintel,
> 
> On Thu, 27 Dec 2012 20:23:48 +0100, Lubomir Rintel wrote:
> 
> >  	dma_sync_single_for_cpu(dma_chan->device->dev, dest_dma,
> >  				MV_XOR_TEST_SIZE, DMA_FROM_DEVICE);
> > +	dma_unmap_single(dma_chan->device->dev, dest_dma, MV_XOR_TEST_SIZE,
> > +			 DMA_FROM_DEVICE);
> 
> I would assume that dma_unmap_single() implies a
> dma_sync_single_for_cpu() since you're unmapping the DMA buffer. So if
> you use dma_unmap_single(), I think you can remove the call to
> dma_sync_single_for_cpu().

Yes, it indeed seems to be the case (comment for arm_dma_unmap_page():
"After this call, reads by the CPU to the buffer are guaranteed to see
whatever the device wrote there.".

> >  	dma_sync_single_for_cpu(dma_chan->device->dev, dest_dma,
> >  				PAGE_SIZE, DMA_FROM_DEVICE);
> > +	dma_unmap_page(dma_chan->device->dev, dest_dma, PAGE_SIZE,
> > +		       DMA_FROM_DEVICE);
> 
> Ditto.
> 
> Also, the mv_xor_memcpy_self_test() function not only dma_map_single()
> the destination buffer, but also the source buffer. So presumably, the
> source buffer should also be dma_unmap_single()'d.
> 
> And for the mv_xor_xor_self_test() function, multiple source buffers
> are dma_map_page()'d, so they should all be dma_unmap_page()'d I guess,
> not only the destination buffer.

Those get released by the mv_xor_run_tx_complete_actions() callback.

I will follow up with an updated patch.

Regards,
Lubo

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