[alsa-devel] multi-channel playback regression

[Takashi Iwai]

At Thu, 23 Jul 2009 14:53:45 +0800,
Wu Fengguang wrote:
> 
> Hi Takashi,
> 
> When doing multi-channel playback tests on IbexPeak, I found that the
> following patch makes the playback enter an infinite loop, repeatedly
> playing a range of ~0.5s audio content. (Seems that some buffer
> pointer can never advance.)

Could you set 1 to /proc/asound/card0/pcm0p/xrun_debug and give the
messages?  Also, please show /proc/.../pcm0p/sub0/hw_params, too.

The change affects only the code path for the problematic hardware
that reports wrong DMA position.  So, if this change regresses, it
means that the device has been already problematic from the
beginning...


Takashi


> 
> Thanks,
> Fengguang
> ---
> 
> 79452f0a28aa5a40522c487b42a5fc423647ad98
> Author: Takashi Iwai <tiwai at suse.de>
> Date:   Wed Jul 22 12:51:51 2009 +0200
> 
>     ALSA: pcm - Fix regressions with VMware
> 
>     VMware tends to report PCM positions and period updates at utterly
>     wrong timing.  This screws up the recent PCM core code that tries
>     to correct the position based on the irq timing.
> 
>     Now, when a backward irq position is detected, skip the update
>     instead of rebasing.  (This is almost the old behavior before
>     2.6.30.)
>     
>     Signed-off-by: Takashi Iwai <tiwai at suse.de>
> 
> diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> index 333e4dd..3b673e2 100644
> --- a/sound/core/pcm_lib.c
> +++ b/sound/core/pcm_lib.c
> @@ -244,18 +244,27 @@ static int snd_pcm_update_hw_ptr_interrupt(struct snd_pcm_substream *substream)
>                         delta = new_hw_ptr - hw_ptr_interrupt;
>         }
>         if (delta < 0) {
> -               delta += runtime->buffer_size;
> +               if (runtime->periods == 1)
> +                       delta += runtime->buffer_size;
>                 if (delta < 0) {
>                         hw_ptr_error(substream,
>                                      "Unexpected hw_pointer value "
>                                      "(stream=%i, pos=%ld, intr_ptr=%ld)\n",
>                                      substream->stream, (long)pos,
>                                      (long)hw_ptr_interrupt);
> +#if 1
> +                       /* simply skipping the hwptr update seems more
> +                        * robust in some cases, e.g. on VMware with
> +                        * inaccurate timer source
> +                        */
> +                       return 0; /* skip this update */
> +#else                  
>                         /* rebase to interrupt position */
>                         hw_base = new_hw_ptr = hw_ptr_interrupt;
>                         /* align hw_base to buffer_size */
>                         hw_base -= hw_base % runtime->buffer_size;
>