linux-kernel - Re: About dma_sync_single_for

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Message-ID: <50178249.7090306@ladisch.de>
Date:	Tue, 31 Jul 2012 08:59:21 +0200
From:	Clemens Ladisch <clemens@...isch.de>
To:	Karl Beldan <karl.beldan@...il.com>
CC:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: About dma_sync_single_for_{cpu,device}

Karl Beldan wrote:
> To tx a chunk of data from the SoC => network device, we :
> - prepare a buffer with a leading header embedding a pattern,
> - trigger the xfer and wait for an irq
> // The device updates the pattern and then triggers an irq
> - upon irq we check the pattern for the xfer completion
>
> I was expecting the following to work:
> 	addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE);

Of both the CPU and the device write to the buffer, you must use
DMA_BIDIRECTIONAL.


Regards,
Clemens
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