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

[Laxman Dewangan]

On Thursday 28 June 2012 06:58 PM, Takashi Iwai wrote:
> 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?

He wanted to refactor allocation part also at same time and so I guessed 
that it will be in some common place and though about the sound/core.

> > 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.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/