Re: ALSA driver problem after standby/resume

["Ville Syrjälä" <syrjala@sci.fi>]

On Mon, Mar 19, 2007 at 03:30:33PM -0400, Rich Rattanni wrote:
> On 3/19/07, Takashi Iwai <tiwai@suse.de> wrote:
> > At Mon, 19 Mar 2007 12:31:16 -0400,
> > Rich Rattanni wrote:
> > >
> > > All:
> > >
> > > I have noticed a strange behaviour in the ALSA driver that seems to be
> > > occur after initiating a power standby and resume.  I am working on an
> > > application that uses FusionSound to playback OGG audio files.  When
> > > the application recognizes it is idle, it tells the OS to enter
> > > standby mode.  Upon resuming from standby, the ALSA API call made by
> > > fusionsound no longer acts as a blocking read, instead it returns
> > > immediately.  I have confirmed this with Denis Oliver Kropp of the
> > > DirectFB / FusionSound project.  He suggested that the ALSA driver
> > > should be repaired to prevent this problem from occuring.
> >
> > It's not clear what is happening there.
> > Do you have a small testcase?
> >
> > When the suspend/resume happens, the apps is usually requested to call
> > snd_pcm_resume() and/or snd_pcm_prepare() appropriately to reset the
> > stream.  Otherwise the PCM status is kept as SUSPENDED.
<snip>
> 
> static void
> device_write( void *device_data, void *samples, unsigned int size )
> {
>      AlsaDeviceData    *data   = device_data;
>      snd_pcm_uframes_t  frames = size;
>      snd_pcm_sframes_t  r;
>      u8                *src;
> 
>      src = samples;
>      while (frames) {
>           r = snd_pcm_writei( data->handle, src, frames );

Maybe we just need to add something like this here?

+          if (r == -ESTRPIPE) {
+               while ((r = snd_pcm_resume( data->handle )) == -EAGAIN)
+                    sleep( 1 );
+          }

>           if (r < 0) {
>                r = snd_pcm_prepare( data->handle );
>                if (r < 0) {
>                     D_WARN( "FusionSound/Device/ALSA: snd_pcm_writei()
> failed: %s\n",
>                             snd_strerror( r ) );
>                     break;
>                }
>                continue;
>           }
>           frames -= r;
>           src += snd_pcm_frames_to_bytes( data->handle, r );
>      }
> }

-- 
Ville Syrjälä
syrjala@sci.fi
http://www.sci.fi/~syrjala/

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