[alsa-devel] Some information about UsbPre2 UAC2 support

Clemens Ladisch clemens at ladisch.de
Sat Jan 26 21:29:10 CET 2013

shal at free.fr wrote:
> For some compatibility raison, Sound device developer want only send a UAC1 configuration when the Operating system is Windows.
> The used method is based on the length of the  setup packet during the device get_descriptor function.
> If the length is 64, the OS is considered as Windows.
> Linux have choosen also this value.

Because there are buggy devices that haven been tested only with Windows
and will blow up if other values are chosen.

I guess somebody has to add a quirk for this device to the driver.

> Now, the USB device descriptor has two configuration descriptors :the first is a UAC1 and the second is a UAC2.
> As UAC1 is a valid configuration descriptor, the usb stack choose this configuration.
> I have patched the usb_choose_configuration() function in file driver/usb/core/generic.c for overwrite the value with the good one.

This can be changed later in the driver with usb_driver_set_configuration().


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