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

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Date:	Thu, 28 Jun 2012 13:09:36 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Laxman Dewangan <ldewangan@...dia.com>
CC:	perex@...ex.cz, broonie@...nsource.wolfsonmicro.com, tiwai@...e.de,
	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

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.

- 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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