linux-kernel - How is dmaengine_prep_slave

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Message-ID: <4F22B593.3010402@metafoo.de>
Date:	Fri, 27 Jan 2012 15:32:51 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Vinod Koul <vinod.koul@...el.com>,
	Russell King <linux@....linux.org.uk>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: How is dmaengine_prep_slave_single supposed to be used?

Hi,

I've tried using dmaengine_prep_slave_single in one of my drivers an run
into an issue, the dma_address attribute of the sg element is not
initialized and thus the dma transfer and the DMA transfer fails.

Quoting from Documentation/dmaengine.txt:

   The peripheral driver is expected to have mapped the scatterlist for
   the DMA operation prior to calling device_prep_slave_sg, and must
   keep the scatterlist mapped until the DMA operation has completed.

So this is clearly not the case with dmaengine_prep_slave_single, so I'm
wondering how is ut supposed to be used and can it work properly at all?

Thanks,
- Lars
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