[alsa-devel] [PATCH v5] ALSA: usb: Work around CM6631 sample rate change bug

[Clemens Ladisch]

Takashi Iwai wrote:
> Torstein Hegge wrote:
>> The C-Media CM6631 USB receiver doesn't respond to changes in sample rate
>> while the interface is active. The same behavior is observed in other UAC2
>> hardware like the VIA VT1731.
>>
>> Reset the interface after setting the sampling frequency on sample rate
>> changes, 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
>> stream, causing distorted sound on sample rate changes.
>>
>> The reset is performed for all UAC2 devices, as it should not affect a
>> standards compliant device, but it is only necessary for C-Media CM6631,
>> VIA VT1731 and possibly others.
>>
>> Failure to read sample rate from the device is not handled as an error in
>> set_sample_rate_v2(), as (permanent or intermittent) failure to read sample
>> rate isn't essential for a successful sample rate set.
>>
>> Signed-off-by: Torstein Hegge <hegge at resisty.net>
>
> What about the latest status of the patch?
>
> If both Clemens and Daniel are happy with it, I can apply it for the
> next 3.9-rc.

Acked-by: Clemens Ladisch <clemens at ladisch.de>
with or without this change:

> Though, it would be nicer if two identical calls of snd_usb_ctl_msg
> can be put into a single function,


Regards,
Clemens