[alsa-devel] [PATCH] ALSA: usb: Work around CM6631 sample rate change bug

[Daniel Mack]

On 02.03.2013 14:04, Torstein Hegge wrote:
> The C-Media CM6631 USB-to-S/PDIF receiver doesn't respond to changes in
> sampling frequency while the interface is active.
> 
> Reset the interface after setting the sampling frequency, to ensure that the
> sample rate set by snd_usb_init_sample_rate() is used. Otherwise, the device
> will try to use the sample rate of the previous file, causing distorted sound
> on sample rate changes.
> 
> Signed-off-by: Torstein Hegge <hegge at resisty.net>

Acked-by: Daniel Mack <zonque at gmail.com>


Thanks!

Daniel


> ---
>  sound/usb/pcm.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
> index d82e378..01978a6 100644
> --- a/sound/usb/pcm.c
> +++ b/sound/usb/pcm.c
> @@ -710,6 +710,16 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
>  		subs->need_setup_ep = false;
>  	}
>  
> +	/* Some devices doesn't respond to sample rate changes while the
> +	 * interface is active. */
> +	switch (subs->stream->chip->usb_id) {
> +	case USB_ID(0x0d8c, 0x0304): /* C-Media - Schiit USB Interface */
> +	case USB_ID(0x0d8c, 0x0309): /* C-Media CM6631 */
> +		usb_set_interface(subs->dev, subs->cur_audiofmt->iface,
> +					subs->cur_audiofmt->altset_idx);
> +		break;
> +	}
> +
>  	/* some unit conversions in runtime */
>  	subs->data_endpoint->maxframesize =
>  		bytes_to_frames(runtime, subs->data_endpoint->maxpacksize);
>