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

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Date:	Mon, 10 Oct 2011 15:23:46 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Vinod Koul <vinod.koul@...el.com>
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 10 October 2011 14:48, Vinod Koul <vinod.koul@...el.com> wrote:
> On Mon, 2011-10-10 at 14:46 +0530, Jassi Brar wrote:
>> On 10 October 2011 12:23, Vinod Koul <vinod.koul@...el.com> wrote:
>> >
>> > +struct dmaxfer_memcpy_template {
>> > +       dma_addr_t src_start;
>> > +       dma_addr_t dst_start;
>> > +       bool src_inc;
>> > +       bool dst_inc;
>> > +       bool src_sgl;
>> > +       bool dst_sgl;
>> > +       size_t numf;
>> > +       size_t frame_size;
>> > +       struct data_chunk sgl[0];
>> > +};
>> > +
>> > +struct dmaxfer_slave_template {
>> > +       dma_addr_t mem;
>> > +       bool mem_inc;
>> > +       size_t numf;
>> > +       size_t frame_size;
>> > +       struct data_chunk sgl[0];
>> > +};
>> >
>> (1) Please tell how is dmaxfer_slave_template supposed to work on
>>  bi-directional channels?
>>  Keeping in mind, dma_slave_config.direction is marked to go away
>>  in future.
> I didn't use dma_slave_config.direction. There is direction field in
> corresponding prepare function.
>
ok but why not reduce 1 argument from api and embed that as
the transfer's property in dmaxfer_slave_template, as I did ?

>>
>> (2)
>>   * slave_template.mem  <=>  memcpy_template.src_start
>>   * slave_template.mem_inc  <=>  memcpy_template.src_inc
>>
>>  So essentially
>>   memcpy_template  :=  slave_template + src/dst_sgl + dst_start + dst_inc
>>
>>  Even after this separation, there is nothing slave specific in
>> dmaxfer_slave_template. The slave client still needs DMA_SLAVE_CONFIG
>> to specify slave parameters of the transfer.
>>  You only save a few bytes in a _copy_ of memcpy_template.
> Yes DMA_SLAVE_CONFIG is always required, this attempt was not aimed to
> remove that, but I would be interested in it :)
>
Sorry then I don't see this "ambiguity"(if there really is any) removal worth
adding an extra prepare when we already have 10 of them.
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