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

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Date:	Thu, 28 Jun 2012 16:10:45 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Laxman Dewangan <ldewangan@...dia.com>
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

At Thu, 28 Jun 2012 19:30:57 +0530,
Laxman Dewangan wrote:
> 
> 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.

Or this could be simply ifdef CONFIG_ARM.
Since this ifdef will be unnecessary soon later, I don't think we need
to give yet another kconfig.  Of course, we should put a good comment
around there for not keeping it for long time.


Takashi
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