linux-kernel - Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

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Date:	Mon, 10 Oct 2011 21:32:39 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	"Williams, Dan J" <dan.j.williams@...el.com>,
	Russell King <rmk@....linux.org.uk>,
	Barry Song <21cnbao@...il.com>, linux-kernel@...r.kernel.org,
	DL-SHA-WorkGroupLinux <workgroup.linux@....com>,
	Dave Jiang <dave.jiang@...el.com>
Subject: Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

On Mon, 2011-10-10 at 16:46 +0530, Jassi Brar wrote:
> On 10 October 2011 16:15, Vinod Koul <vinod.koul@...el.com> wrote:
> >
> > But I am fine if we find a common ground and merge the two where dmac
> > can cleanly identify direction and mode it is operating.
> >
> The client would set the xfer_direction and dmac would interpret as
> 
> enum xfer_direction {
>      MEM_TO_MEM,   ->  Async/Memcpy mode
>      MEM_TO_DEV,    ->  Slave mode & From Memory to Device
>      DEV_TO_MEM,    ->  Slave mode & From Device to Memory
>      DEV_TO_DEV,     ->  Slave mode & From Device to Device
> }
> 
> How could it get any cleaner?
Consider the case of a dmac driver which supports interleaved dma as
well as memcpy and slave
It needs to interpret dma_data_direction for later cases and
xfer_direction for former ones. Not a clean way to convey same info. And
only reason why we cannot use dma_data_direction here is because we
don't know the "mode", by splitting we overcome that.

-- 
~Vinod

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