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

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Date:	Wed, 12 Oct 2011 13:41:48 +0800
From:	Barry Song <21cnbao@...il.com>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	Russell King <rmk@....linux.org.uk>,
	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

2011/10/11 Jassi Brar <jaswinder.singh@...aro.org>:
> On 10 October 2011 21:32, Vinod Koul <vinod.koul@...el.com> wrote:
>> 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.
> dma_data_direction is the mapping attribute of a buffer and is not meant to
> tell type of source and destination of a transfer.
> xfer_direction is meant for that purpose.
> So I'd rather convert device_prep_dma_cyclic and device_prep_slave_sg
> to use xfer_direction.

i tend to agree with Jassi. now dma_data_direction actually is only
mapping things not real transfer direction.
xfer_direction is now something really telling the data transfer direction.
I think that's what device_prep_dma_cyclic and device_prep_slave_sg want.

actually, there is only one case we need to use dma_data_direction in
dmac driver, that's unmapping async dma buffer.
But the param to dma_unmap_single can be implied by xfer_direction and
dma description.

that's why i think we should rename dma_data_direction to
dma_map_direction or something like that to avoid confusion.

-barry
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