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Subject: Re: [alsa-devel] ALSA:usb audio Higher sample rates on usb audio no
 longer working.
To:     Takashi Iwai <tiwai@suse.de>, Con Kolivas <kernel@kolivas.org>
Cc:     saranya.gopal@intel.com, alsa-devel@alsa-project.org,
        linux-usb@vger.kernel.org,
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        felipe.balbi@linux.intel.com
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From:   Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
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Date:   Fri, 4 Jan 2019 09:23:38 -0600
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> [ 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.

-Pierre