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

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Message-Id: <20090724.222919.240484146.anemo@mba.ocn.ne.jp>
Date:	Fri, 24 Jul 2009 22:29:19 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	nicolas.ferre@...el.com
Cc:	dan.j.williams@...el.com, maciej.sosnowski@...el.com,
	linux-arm-kernel@...ts.arm.linux.org.uk, patrice.vilchez@...el.com,
	linux-kernel@...r.kernel.org, haavard.skinnemoen@...el.com
Subject: Re: [PATCH] dmaengine: at_hdmac: add DMA slave transfers

On Fri, 24 Jul 2009 09:35:37 +0200, Nicolas Ferre <nicolas.ferre@...el.com> wrote:
> > Seems straightforward and self contained, applied.  Just curious which
> > drivers will take advantage of this slave capability?  As it stands I
> > do not see any in-tree users of at_hdmac beyond dmatest?
> 
> Well, in fact the same as dw_dmac: atmel-mci. Adaptation of other
> drivers are coming: probably ac97 and spi interfaces.
> 
> The patches for adaptation of atmel-mci to at_hdmac are coming...

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.

It is not clear for me how dma driver should handle unmapping on
completion of slave DMA.  Are there any consensus on it?

I enclosed unmapping code of txx9dmac driver by "if (!slave)" and did
not use DMA_COMPL_SKIP_XXX_UNMAP flag in its client driver (txx9aclc
ASoC driver).  If consensus made on how to handle unmapping on slave
DMA, I will follow it.

---
Atsushi Nemoto
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