Re: [alsa-devel] [PATCH] ASoC: snd_dmaengine: add common api forpcm_mmap

[Laxman Dewangan]

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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