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

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Date:   Fri, 4 Jan 2019 11:13:29 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     "Gopal, Saranya" <saranya.gopal@...el.com>,
        Takashi Iwai <tiwai@...e.de>, Con Kolivas <kernel@...ivas.org>
Cc:     "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "felipe.balbi@...ux.intel.com" <felipe.balbi@...ux.intel.com>
Subject: Re: [alsa-devel] ALSA:usb audio Higher sample rates on usb audio no
 longer working.


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.
>>
>> -Pierre
> 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