[alsa-devel] Some information about UsbPre2 UAC2 support

Clemens Ladisch clemens at ladisch.de
Mon Jan 28 15:17:01 CET 2013

shal at free.fr wrote:
>>> I have to plug/unplug the sound card in order to have 2 configurations
>>> descriptor for this device.
>> That's strange; the get_descriptor request should be the same.
> - I used a standard kernel (with 64 as get_descriptor buffer size)
> ...
> - I reboot with modified kernel (with 65 as get_descriptor buffer size)
> ...
> - Now the sound card provides a UAC1+UAC2 configuration

So the modified get_descriptor is stil necessary.

> - I performed a usb_reset()
> - I performed a get_descriptor using a usb_control() with 65 as buffer size

The USB core will already issue the get_descriptor request before
the driver gets informed that the device is there, so this won't


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