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

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Date:	Thu, 28 Jun 2012 15:28:45 +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 18:34:02 +0530,
Laxman Dewangan wrote:
> 
> 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.

Which 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.

Way too much hustles than necessary...


Takashi
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