linux-kernel - Re: [PATCH] dmaengine: at_hdmac: add DMA slave transfers

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Message-Id: <20090729.001330.172537373.anemo@mba.ocn.ne.jp>
Date:	Wed, 29 Jul 2009 00:13:30 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	maciej.sosnowski@...el.com
Cc:	haavard.skinnemoen@...el.com, nicolas.ferre@...el.com,
	dan.j.williams@...el.com, linux-arm-kernel@...ts.arm.linux.org.uk,
	patrice.vilchez@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: at_hdmac: add DMA slave transfers

On Mon, 27 Jul 2009 14:24:26 +0100, "Sosnowski, Maciej" <maciej.sosnowski@...el.com> wrote:
> >> Your atc_chain_complete() calls dma_unmap_xxx unless
> >> DMA_COMPL_SKIP_XXX_UNMAP specified.  But atmel-mci driver does not set
> >> the flag on dma_async_tx_descriptor.  I suppose one of them should be
> >> fixed.
> > 
> > atmel-mci should definitely set that flag.
> > 
> > Haavard
> 
> I agree with Haavard.

Then, what should dma driver do when client driver did not set these
flags?  If it should call dma_unmap_sg(), the dma driver should keep
sg and direction somewhere...

Also, calling dma_map_sg() in its prep_slave_sg function will not fit
for sound drivers, which use DMA buffers prepared in its framework.

For slave DMA, doing all mapping/unmapping in DMA client is better,
isn't it?

---
Atsushi Nemoto
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