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

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Date:	Thu, 28 Jun 2012 14:15:38 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Laxman Dewangan <ldewangan@...dia.com>, perex@...ex.cz,
	broonie@...nsource.wolfsonmicro.com, lrg@...com,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	swarren@...dia.com
Subject: Re: [PATCH] ASoC: snd_dmaengine: add common api for pcm_mmap

At Thu, 28 Jun 2012 13:09:36 +0200,
Lars-Peter Clausen wrote:
> 
> On 06/28/2012 09:01 AM, Laxman Dewangan wrote:
> > The pcm mmap for the substream dma buffer is done using the
> > dma_mmap_writecombine().
> > Some of the chip sound driver like Spear, Tegra, Davinci,
> > ep93xx,snd_imx, snd_mxs, NUC900, OMAP, Samsung are doing this
> > mapping locally.
> > Add api in the snd dmaengine driver so that different client of
> > snd dmaengine can use this rather than implementing locally.
> > 
> 
> This is not really related to the dmaengine pcm driver. It's more of a
> coincidence that all upstream drivers which use the dmaengine pcm driver
> also use write-combined memory. In my opinion it would be better to add this
> to the ALSA core. Now that there is a generic dma_mmap_writecombine it may
> make sense to integrate this with snd_pcm_lib_default_mmap.

Agreed.

Also, it must be portable.  So far, only ARM has
dma_mmap_writecombine(), thus the build on other arch would fail as
is.


thanks,

Takashi

> 
> - Lars
> 
> > Signed-off-by: Laxman Dewangan <ldewangan@...dia.com>
> > ---
> >  include/sound/dmaengine_pcm.h |    2 ++
> >  sound/soc/soc-dmaengine-pcm.c |   17 +++++++++++++++++
> >  2 files changed, 19 insertions(+), 0 deletions(-)
> > 
> > diff --git a/include/sound/dmaengine_pcm.h b/include/sound/dmaengine_pcm.h
> > index b877334..15c0d3c 100644
> > --- a/include/sound/dmaengine_pcm.h
> > +++ b/include/sound/dmaengine_pcm.h
> > @@ -47,4 +47,6 @@ int snd_dmaengine_pcm_close(struct snd_pcm_substream *substream);
> >  
> >  struct dma_chan *snd_dmaengine_pcm_get_chan(struct snd_pcm_substream *substream);
> >  
> > +int snd_dmaengine_pcm_mmap_writecombine(struct snd_pcm_substream *substream,
> > +		struct vm_area_struct *vma);
> >  #endif
> > diff --git a/sound/soc/soc-dmaengine-pcm.c b/sound/soc/soc-dmaengine-pcm.c
> > index 5df529e..6535eb3 100644
> > --- a/sound/soc/soc-dmaengine-pcm.c
> > +++ b/sound/soc/soc-dmaengine-pcm.c
> > @@ -21,6 +21,7 @@
> >  #include <linux/module.h>
> >  #include <linux/init.h>
> >  #include <linux/dmaengine.h>
> > +#include <linux/dma-mapping.h>
> >  #include <linux/slab.h>
> >  #include <sound/pcm.h>
> >  #include <sound/pcm_params.h>
> > @@ -313,3 +314,19 @@ int snd_dmaengine_pcm_close(struct snd_pcm_substream *substream)
> >  	return 0;
> >  }
> >  EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_close);
> > +
> > +/**
> > + * snd_dmaengine_pcm_mmap_writecombine - mmap stream dma buffer using
> > + * dma_mmap_writecombine().
> > + * @substream: PCM substream
> > + * @vma: VM area.
> > + */
> > +int snd_dmaengine_pcm_mmap_writecombine(struct snd_pcm_substream *substream,
> > +			struct vm_area_struct *vma)
> > +{
> > +	struct snd_pcm_runtime *runtime = substream->runtime;
> > +
> > +	return dma_mmap_writecombine(substream->pcm->card->dev, vma,
> > +		runtime->dma_area, runtime->dma_addr, runtime->dma_bytes);
> > +}
> > +EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_mmap_writecombine);
> 
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