linux-kernel - Re: [RFC v3 4/7] dmaengine: Add slave DMA interface

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Message-ID: <20080213202402.22818482@siona>
Date:	Wed, 13 Feb 2008 20:24:02 +0100
From:	Haavard Skinnemoen <hskinnemoen@...el.com>
To:	"Dan Williams" <dan.j.williams@...el.com>
Cc:	linux-kernel@...r.kernel.org,
	"Shannon Nelson" <shannon.nelson@...el.com>,
	"David Brownell" <david-b@...bell.net>, kernel@...32linux.org,
	"Francis Moreau" <francis.moro@...il.com>,
	"Paul Mundt" <lethal@...ux-sh.org>,
	"Vladimir A. Barinov" <vbarinov@...mvista.com>,
	"Pierre Ossman" <drzeus-list@...eus.cx>
Subject: Re: [RFC v3 4/7] dmaengine: Add slave DMA interface

On Wed, 13 Feb 2008 12:07:26 -0700
"Dan Williams" <dan.j.williams@...el.com> wrote:

> > +struct dma_slave_descriptor {
> > +       struct dma_async_tx_descriptor txd;
> > +       struct list_head client_node;
> > +};  
> 
> Can you explain a bit why client_node is needed?  I do not think we
> need dma_slave_descriptor if dma_unmap data / control is added to
> dma_async_tx_descriptor.  Hmm?

Well, it's perhaps not needed for slave transfers as such. But the MMC
driver (and I suspect quite a few other users of the slave interface)
deals with scatterlists, so it needs a way to keep track of all the
descriptors it submits. Hence the list node.

But looking at your latest patch series, I guess we can use the new
"next" field instead. It's not like we really need the full
capabilities of list_head.

Haavard
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