[alsa-devel] [PATCH 6/9] rate: handle negative values from snd_pcm_mmap_playback_hw_avail

[Takashi Iwai]

At Sun, 14 Sep 2014 00:30:18 +0600,
Alexander E. Patrakov wrote:
> 
> Such negative returns are possible during an underrun if xrun detection
> is disabled.
> 
> So, don't store the result in an unsigned variable (where it will
> overflow), and postpone the trigger in such case, too.
> 
> Signed-off-by: Alexander E. Patrakov <patrakov at gmail.com>
> ---
> 
> The patch is only compile-tested and the second hunk may well be wrong.
> 
> There are also similar issues in pcm_share.c, but, as I don't completely
> understand the code there and cannot test that plugin at all due to
> unrelated crashes, there will be no patch from me.

In general, hw_avail must not be negative before starting the stream.
If it is, then it means most likely the driver problem, so we should
return error immediately instead.


Takashi

> 
>  src/pcm/pcm_rate.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/pcm/pcm_rate.c b/src/pcm/pcm_rate.c
> index b436a8e..736d558 100644
> --- a/src/pcm/pcm_rate.c
> +++ b/src/pcm/pcm_rate.c
> @@ -1058,7 +1058,7 @@ static snd_pcm_state_t snd_pcm_rate_state(snd_pcm_t *pcm)
>  static int snd_pcm_rate_start(snd_pcm_t *pcm)
>  {
>  	snd_pcm_rate_t *rate = pcm->private_data;
> -	snd_pcm_uframes_t avail;
> +	snd_pcm_sframes_t avail;
>  		
>  	if (pcm->stream == SND_PCM_STREAM_CAPTURE)
>  		return snd_pcm_start(rate->gen.slave);
> @@ -1069,7 +1069,7 @@ static int snd_pcm_rate_start(snd_pcm_t *pcm)
>  	gettimestamp(&rate->trigger_tstamp, pcm->tstamp_type);
>  
>  	avail = snd_pcm_mmap_playback_hw_avail(rate->gen.slave);
> -	if (avail == 0) {
> +	if (avail <= 0) {
>  		/* postpone the trigger since we have no data committed yet */
>  		rate->start_pending = 1;
>  		return 0;
> -- 
> 2.1.0
>