[alsa-devel] [PATCH] alsa: provide a more useful get_unmapped_area handler for pcm

[Takashi Iwai]

At Tue,  9 Mar 2010 12:57:52 -0500,
Mike Frysinger wrote:
> 
> From: Daniel Glöckner <dg at emlix.com>
> 
> Shared memory mappings on nommu machines require a get_unmapped_area
> file operation that suggests an address for the mapping. The current
> implementation returns 0 and thus forces the driver to implement an
> mmap handler that fixes up the start and end address of the vma.
> 
> This patch returns the address of the dma buffer, so it should work
> out of the box for all drivers that use the snd_pcm_runtime->dma_area
> pointer.
> 
> Addresses for mapping the status and control pages are returned as
> well, but to make those work the conditional compilation of
> snd_pcm_mmap_{status,control} would need to be revised.
> 
> URL: http://thread.gmane.org/gmane.linux.alsa.devel/61230
> Signed-off-by: Daniel Glöckner <dg at emlix.com>
> Signed-off-by: Cliff Cai <cliff.cai at analog.com>
> Signed-off-by: Mike Frysinger <vapier at gentoo.org>
> ---
> this has been posted before but didnt seem to get any feedback ...

Looks so.
Now I applied the patch.  I'll add it for 2.6.34 merge, too.

This doesn't work for every case, though.  But the irregular cases
without dma_area setup don't provide mmap usually, so mostly OK :)


thanks,

Takashi


> 
>  sound/core/pcm_native.c |   30 ++++++++++++++++++++++--------
>  1 files changed, 22 insertions(+), 8 deletions(-)
> 
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index 8728876..9681518 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -3434,14 +3434,28 @@ out:
>  #endif /* CONFIG_SND_SUPPORT_OLD_API */
>  
>  #ifndef CONFIG_MMU
> -unsigned long dummy_get_unmapped_area(struct file *file, unsigned long addr,
> -				      unsigned long len, unsigned long pgoff,
> -				      unsigned long flags)
> -{
> -	return 0;
> +static unsigned long snd_pcm_get_unmapped_area(struct file *file,
> +					       unsigned long addr,
> +					       unsigned long len,
> +					       unsigned long pgoff,
> +					       unsigned long flags)
> +{
> +	struct snd_pcm_file *pcm_file = file->private_data;
> +	struct snd_pcm_substream *substream = pcm_file->substream;
> +	struct snd_pcm_runtime *runtime = substream->runtime;
> +	unsigned long offset = pgoff << PAGE_SHIFT;
> +
> +	switch (offset) {
> +	case SNDRV_PCM_MMAP_OFFSET_STATUS:
> +		return (unsigned long)runtime->status;
> +	case SNDRV_PCM_MMAP_OFFSET_CONTROL:
> +		return (unsigned long)runtime->control;
> +	default:
> +		return (unsigned long)runtime->dma_area + offset;
> +	}
>  }
>  #else
> -# define dummy_get_unmapped_area NULL
> +# define snd_pcm_get_unmapped_area NULL
>  #endif
>  
>  /*
> @@ -3460,7 +3474,7 @@ const struct file_operations snd_pcm_f_ops[2] = {
>  		.compat_ioctl = 	snd_pcm_ioctl_compat,
>  		.mmap =			snd_pcm_mmap,
>  		.fasync =		snd_pcm_fasync,
> -		.get_unmapped_area =	dummy_get_unmapped_area,
> +		.get_unmapped_area =	snd_pcm_get_unmapped_area,
>  	},
>  	{
>  		.owner =		THIS_MODULE,
> @@ -3473,6 +3487,6 @@ const struct file_operations snd_pcm_f_ops[2] = {
>  		.compat_ioctl = 	snd_pcm_ioctl_compat,
>  		.mmap =			snd_pcm_mmap,
>  		.fasync =		snd_pcm_fasync,
> -		.get_unmapped_area =	dummy_get_unmapped_area,
> +		.get_unmapped_area =	snd_pcm_get_unmapped_area,
>  	}
>  };
> -- 
> 1.7.0.2
>