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

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Date:	Wed, 29 Jul 2009 14:05:17 +0100
From:	"Sosnowski, Maciej" <maciej.sosnowski@...el.com>
To:	Atsushi Nemoto <anemo@....ocn.ne.jp>
CC:	"haavard.skinnemoen@...el.com" <haavard.skinnemoen@...el.com>,
	"nicolas.ferre@...el.com" <nicolas.ferre@...el.com>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.arm.linux.org.uk" 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	"patrice.vilchez@...el.com" <patrice.vilchez@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] dmaengine: at_hdmac: add DMA slave transfers

Atsushi Nemoto wrote:
> 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...

Well, what about BUG_ON?

> 
> 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.

It looks like a need for one more flag: DMA_SKIP_MAP_SG.
What do you think?

Regards,
Maciej
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