linux-kernel - Re: [PATCHv5] DMAEngine: Define interleaved transfer request api

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Date:	Fri, 14 Oct 2011 19:21:45 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Barry Song <21cnbao@...il.com>, linux-kernel@...r.kernel.org,
	dan.j.williams@...el.com, rmk@....linux.org.uk,
	DL-SHA-WorkGroupLinux <workgroup.linux@....com>
Subject: Re: [PATCHv5] DMAEngine: Define interleaved transfer request api

On 14 October 2011 19:01, Vinod Koul <vinod.koul@...el.com> wrote:
> On Fri, 2011-10-14 at 17:21 +0530, Jassi Brar wrote:
>> On 14 October 2011 13:02, Barry Song <21cnbao@...il.com> wrote:
>> >
>> > what if i want a cyclic interleaved transfer? i think the cyclic
>> > interleaved transfer is what i want for audio dma.
>> >
>> ... we need to restore 'bool frm_irq' and add new 'bool cyclic' that
>> would replay the transfer(i.e, reset dma-pointers to src_start & dst_start)
>> after 'numf' frames have been transferred.
> I was thinking more on lines to have this conveyed thru a flag.
>
Sorry don't see exactly what you mean.
frm_irq and numf are independent of each other and could
cover more cases than a single flag.

> Anyway I plan to work on merging device_prep_slave_sg and
> device_prep_cyclic to single API. Think more of device_prep_cyclic as
> special case with sg length one and flag to tell dmac its cyclic.
>
AFAIK, usually the ring buffer is divided into N (>1) different
periods that need
to be transferred in endless loop.

> Similarly here we could use/define this flag to say this transfer is
> also cyclic in nature and dmac then reloads the list again.
> That way any prep can be made cyclic in nature by just using this flag.
>
Some cyclic transfers might want callback done after each period/frame
while some not. We can't cover using just one flag.
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