linux-kernel - Re: [PATCH 2/3] ARM: edma: Rename header file for dmaengine filter function definition

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Message-ID: <5478611A.5060404@ti.com>
Date:	Fri, 28 Nov 2014 13:48:42 +0200
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<alsa-devel@...a-project.org>, <linux-omap@...r.kernel.org>,
	<linux@....linux.org.uk>, <vinod.koul@...el.com>,
	<linux-mmc@...r.kernel.org>, <nsekhar@...com>,
	Liam Girdwood <lgirdwood@...il.com>,
	<linux-kernel@...r.kernel.org>, <khilman@...prootsystems.com>,
	Tony Lindgren <tony@...mide.com>,
	Mark Brown <broonie@...nel.org>, <chris@...ntf.net>,
	<dmaengine@...r.kernel.org>, <ulf.hansson@...aro.org>,
	<linux-spi@...r.kernel.org>
Subject: Re: [PATCH 2/3] ARM: edma: Rename header file for dmaengine filter
 function definition

On 11/28/2014 12:51 PM, Arnd Bergmann wrote:
> On Friday 28 November 2014 09:16:24 Peter Ujfalusi wrote:
>> On 11/27/2014 11:52 PM, Arnd Bergmann wrote:
>>> On Thursday 27 November 2014 20:46:12 Peter Ujfalusi wrote:
>>>>
>>>> I see. With this series I did not planed to fix all edma related issues, just
>>>> as a start clean up the related header files. I would rather not add fixes to
>>>> mmc, spi, etc drivers since while you have valid point it is not in the scope
>>>> of this series.
>>>> Can we do the changes you are suggesting in an incremental manner?
>>>
>>> Sure, but I'd leave the existing filter function declaration alone then
>>> and not move it, since we wouldn't want to keep it in the long run.
>>
>> but if you want to reference the filter function (which is in
>> drivers/dma/edma.c) in arch/arm/mach-davinci/ directory, we will need it.
>> Don't we?
> 
> Yes, unless you move the definition of the filter function into
> arch/arm/common/edma.c or arch/arm/mach-davinci/devices.c, but that
> would require other changes.

At the end the aim is to get rid of the edma code form arch/arm and have only
dmaengine API towards eDMA. The ASoC davinci-pcm is the only user of the
legacy API AFAIK. It has a mode called ping-pong which is not possible with
the dmaeingine at all. This is to overcome underflow situations on parts where
the audio IP does not have FIFO.
My edma-pcm (which is using dmaengine) should be able to handle this
situation, but I need to verify it before I can remove the davinci-pcm and
then we can get rid of the direct eDMA API and code.

>> If I leave the header as it is, then how would we clean up the edma headers? I
>> would not put the API definitions for the arch code into the same file as we
>> have the filter definition.
> 
> Ok, just go ahead with your current patch then, we can always follow up.
> The most important cleanup for edma is elsewhere anyway, so once the asoc
> drivers can use the dmaengine interface, this should be easier.
> 
> 	Arnd
> 


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