Re: [alsa-devel] ALSA:usb audio Higher sample rates on usb audio no longer working.

From: Pierre-Louis Bossart
Date: Fri Jan 04 2019 - 12:13:34 EST

On 1/4/19 10:52 AM, Gopal, Saranya wrote:
[ Adding linux-usb ML to Cc, as it's a core USB issue ]

So the device seems incorrectly advertising as if it were supporting
UAC3 -- assuming the device is still not UAC3-capable.

IOW, it's a buggy firmware. We need some blacklisting, or revert the
commit for now, unless any real UAC3 device comes up to the market.
IIRC an UAC3-capable device is required to expose a backwards-compatible
configuration (either UAC1 or UAC2). Maybe an additional test can be
done to harden the detection so that UAC3 is only chosen if indeed a
second audio configuration is present as well.

I also vaguely recall there was talk about adding information in the BOS
descriptor, but I don't know if this was ever published.

The current detection logic is that UAC3 configuration is chosen only when a device has a configuration with audio interface supporting UAC3 protocol.
Additionally, it already makes sure that UAC3 is selected only when there is more than one configuration.
What I meant if that the other configurations are not checked for UAC1 or UAC2 capabilities, you only check that there is more than one configuration