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

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Date:	Thu, 28 Jun 2012 19:30:57 +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 07:21 PM, Takashi Iwai wrote:
> At Thu, 28 Jun 2012 19:06:07 +0530,
> Laxman Dewangan wrote:
>
>>>> 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.
>>> Way too much hustles than necessary...
>> Ooh no. :-(  I had taken the idea from snd_dmaengine_pcm driver.
>> Bit I like to hear simple way which solves the purpose.
> As Lars suggested, a simple ifdef should suffice for now.
> With the upcoming generic dma_mmap_writecombine() stuff, it'd be even
> simpler in future.
>
> But, still we need to be careful about this.  As mentioned, there is
> no flag to know the possibility of writecombine mmap beforehand.
> It'd be nice if we have either a compile-time or a run-time flag /
> function to check that.  Then the driver can also expose the mmap
> capability to user-space depending on the flag.

Yaah, this seems really simple. Thanks for suggestion.
If I understand it fully, the new apis will be declare in sound/pcm.h, 
implement it in pcm_native.c and use the config variable
CONFIG_SND_PCM_WRITECOMBINE_BUFFER for ifdef.

This will be selected in required sound/soc driver so they can use it 
like powerpc (for fsl) and ARM arch based soc.

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