SNDRV_PCM_IOCTL_START
snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_START, NULL);
cmd = SNDRV_PCM_IOCTL_START;
cmd = SNDRV_PCM_IOCTL_START;
case SNDRV_PCM_IOCTL_START:
case SNDRV_PCM_IOCTL_START:
case SNDRV_PCM_IOCTL_START: