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

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Date:	Mon, 3 Oct 2011 21:49:43 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Russell King <rmk@....linux.org.uk>
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 3 October 2011 21:43, Russell King <rmk@....linux.org.uk> wrote:
> 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.
>
The proposed api is usable by both Slave as well as Async(Memcpy etc).
So it *does* matter here.
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