[alsa-devel] [PATCH alsa-lib] pcm: fix snd_pcm_mmap_hw_avail() near the boundary

[Takashi Iwai]

At Sun, 31 Aug 2014 22:23:47 +0600,
Alexander E. Patrakov wrote:
> 
> This function returned incorrect results when hw.ptr was near the
> boundary and hw.appl_ptr was near zero. Here "incorrect" means "greater
> than the boundary".
> 
> The result was incorrect, because it was used as a return value of
> various *_rewindable() functions and also as the delay for ioplug.
> 
> Signed-off-by: Alexander E. Patrakov <patrakov at gmail.com>

Hrm, the very early version of snd_pcm_mmap_hw_avail() was correctly
implemented:

static inline ssize_t snd_pcm_mmap_hw_avail(snd_pcm_t *pcm)
{
       if (pcm->stream == SND_PCM_STREAM_PLAYBACK)
               return snd_pcm_mmap_playback_hw_avail(pcm);
       else
               return snd_pcm_mmap_capture_hw_avail(pcm);
}

Since the commit 9a435c2d934a, the breakage was introduced there.
I have no idea what and why this was done so, it's a really old commit
more than a decade ago.

In anyway, your fix look good and simple, so I applied it as is now,
instead of reverting to the old version above.

BTW, at the next done, don't forget to put maintainers to Cc.


thanks,

Takashi

> ---
>  src/pcm/pcm_local.h | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/src/pcm/pcm_local.h b/src/pcm/pcm_local.h
> index 80bbe59..74ebd60 100644
> --- a/src/pcm/pcm_local.h
> +++ b/src/pcm/pcm_local.h
> @@ -461,13 +461,7 @@ static inline snd_pcm_sframes_t snd_pcm_mmap_capture_hw_avail(snd_pcm_t *pcm)
>  
>  static inline snd_pcm_sframes_t snd_pcm_mmap_hw_avail(snd_pcm_t *pcm)
>  {
> -	snd_pcm_sframes_t avail;
> -	avail = *pcm->hw.ptr - *pcm->appl.ptr;
> -	if (pcm->stream == SND_PCM_STREAM_PLAYBACK)
> -		avail += pcm->buffer_size;
> -	if (avail < 0)
> -		avail += pcm->boundary;
> -	return pcm->buffer_size - avail;
> +	return pcm->buffer_size - snd_pcm_mmap_avail(pcm);
>  }
>  
>  static inline const snd_pcm_channel_area_t *snd_pcm_mmap_areas(snd_pcm_t *pcm)
> -- 
> 2.1.0
> 
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