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

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Date:	Fri, 4 Jan 2013 17:10:33 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Lubomir Rintel <lkundrak@...sk>
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

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().

>  	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.

Does that make sense?

Thanks,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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