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

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Date:	Wed, 12 Oct 2011 14:53:34 +0800
From:	Barry Song <21cnbao@...il.com>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Jassi Brar <jaswinder.singh@...aro.org>,
	"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

2011/10/12 Vinod Koul <vinod.koul@...el.com>:
> On Wed, 2011-10-12 at 13:41 +0800, Barry Song wrote:
>> 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.
> Nope, I would leave dma_data_direction as is.
> We should use above enum in dmaengine and all dmac drivers.

anyway, the rename issue is trivial. i can accept the current name as
is even it doesn't make all senses.
The important thing is the dma_transfer_direction or
dma_xfer_direction as Jassi and you said.

>
> @Jassi: I have started doing this change for dmaengine and dmacs, and I
> took the liberty to name this enum as dma_transfer_direction, hope you
> are okay with that
>
>
> --
> ~Vinod
>
-barry
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