linux-kernel - Re: [alsa-devel] [PATCH] ASoC: snd_dmaengine: add common api for pcm

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Date:	Thu, 28 Jun 2012 18:34:02 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Takashi Iwai <tiwai@...e.de>
CC:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	Stephen Warren <swarren@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lrg@...com" <lrg@...com>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [alsa-devel] [PATCH] ASoC: snd_dmaengine: add common api for
 pcm_mmap

On Thursday 28 June 2012 06:27 PM, Takashi Iwai wrote:
> At Thu, 28 Jun 2012 18:05:53 +0530,
> Laxman Dewangan wrote:
>> On Thursday 28 June 2012 05:58 PM, Mark Brown wrote:
>>> * PGP Signed by an unknown key
>>>
>>> On Thu, Jun 28, 2012 at 02:30:26PM +0200, Lars-Peter Clausen wrote:
>>>> On 06/28/2012 02:18 PM, Mark Brown wrote:
>>>>> Oh, dear - this means we don't actually have a generic API at all.  Is
>>>>> there any effort being made to make this generally available?
>>>> Yes there is, and in fact in next/master there is generic
>>>> dma_mmap_writecombine. I'm not quite sure how it behaves on non ARM archs
>>>> though. But in theory it should fallback to a normal coherent mapping. Marek
>>>> did a lot of work on this, I've put him on Cc.
>> So can we put the function snd_pcm_lib_writecombine_mmap() in the
>> pcm_native.c and only export this api for ARM i.e.  under macro  #ifdef
>> CONFIG_ARM so that ARM based SOCs like Tegra/epa3xx/mxs/spear can
>> directly use that one?
>> Or, wait for this common API until all ARCH support it?
> I think it's fine to put it first in ALSA side with some ifdef.
> A similar trick is already found for snd_pcm_lib_mmap_iomem.
> See include/sound/pcm.h.
>
> But, actually it's a still question what if an architecture doesn't
> support the mmap of writecombine at all.  The proposed patch doesn't
> allow you to know whether writecombine-mmap is possible or not on the
> running architecture until you really try to call it and fail.
> It's a missing piece, IMO.

Lars wanted to move the buffer allocation also to common place.
Then how about this?
create new file and header for snd-pcm-writecombine-buffer.c/.h and put 
this in sound/core.
Select this file compilation through config SND_PCM_WRITECOMBINE_BUFFER 
which will be select this config through sound/soc/xxx/Kconfig if they 
want to use.
This will provide three apis: new, free and mmap.




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