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

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Message-ID: <20111003161349.GB28287@flint.arm.linux.org.uk>
Date:	Mon, 3 Oct 2011 17:13:49 +0100
From:	Russell King <rmk@....linux.org.uk>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	Barry Song <21cnbao@...il.com>, Vinod Koul <vinod.koul@...el.com>,
	linux-kernel@...r.kernel.org, dan.j.williams@...el.com,
	DL-SHA-WorkGroupLinux <workgroup.linux@....com>
Subject: Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

On Mon, Oct 03, 2011 at 11:54:23AM +0530, Jassi Brar wrote:
> On 2 October 2011 06:03, Barry Song <21cnbao@...il.com> wrote:
> > 2011/10/2 Jassi Brar <jaswinder.singh@...aro.org>
> 
> >> > For example, it can't use
> >> > MEM_TO_MEM to map, it still need to know whether the memory is source
> >> > or dest.
> >> MEM_TO_MEM means "From Memory Source To Memory Destination"
> >>  Map Src buffer with DMA_TO_DEVICE and Dst buffer with DMA_FROM_DEVICE
> >>
> >> MEM_TO_DEV means "From Memory Source To FIFO Destination"
> >>  Map Src buffer with DMA_TO_DEVICE.
> >>
> >> DEV_TO_MEM means "From FIFO Source To Memory Destination"
> >>  Map Dst buffer with DMA_FROM_DEVICE
> >>
> >> DEV_TO_DEV means "From FIFO Source To FIFO Destination"
> >>
> >> What else would you want to know ?
> >
> > that is the problem. for example, drivers can't use MEM_TO_MEM as a
> > flag to do dma mapping. so xfer_direction can't cover all that
> > dma_data_direction can do.  that's why you need both
> > dma_data_direction and xfer_direction with some similar flags in them.
> >
> The client drivers map the src/dst buffers and the dmac driver unmaps
> them by default(!). For which, the dmac driver doesn't look at anything
> other than
>      DMA_COMPL_SKIP_SRC/DST_UNMAP
>      DMA_COMPL_SRC/DST_UNMAP_SINGLE
>   bits of 'enum dma_ctrl_flags'.
> For this unmap'ing purpose, the usage of dma_data_direction is already
> internal to the dmac driver.

No.  Slave DMA engine drivers do *not* (and if they do, they should *not*)
honour the unmapping of submitted buffers.

The unmapping of these buffers by the DMA engine driver is intended to be
done for the async_tx API and not slave DMA.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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