Re: [alsa-devel] [PATCH] ASoC: pcm: allow changing the playback/capture rates for symmetric links

On Wed, Apr 27, 2016 at 10:49:19AM +0200, Peter Rosin wrote:

The below program fails on a dai link with symmetric rates without this patch. The patch makes it work.

You've not articulated the problem you're trying to fix here, what in concrete terms is the program trying to accomplish and why should it succeed?

if ((fd = open("/dev/dsp", O_WRONLY, 0)) == -1) {
        perror("open");
        return 1;
}

This is using the OSS interfaces which really haven't ever been especially supported for ASoC.

• if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {

• if (!cpu_dai->capture_active)
  

• 	return 0;
  

• } else if (substream->stream == SNDRV_PCM_STREAM_CAPTURE) {

• if (!cpu_dai->playback_active)
  

• 	return 0;
  

• }
• rate = params_rate(params); channels = params_channels(params); sample_bits = snd_pcm_format_physical_width(params_format(params));

This means we've opened up a race where the stream is configured but not started where the opposite direction can configure a different setup. Since starting both directions very close together is a common operation it seems likely to cause issues.