Hi. I have a patch lying around for some month now and would need some hints how to correctly implement it.

1. What's the correct way to save the state of a special feature? There is a switch which turns on a certain feature in the usb mixer. Looking at the struct usb_mixer_interface I implemented it similar to "audigy2nx_leds" - by adding a new u8 (and the necessary functions).

2. Should one rather set ignore_ctl_error to 1 (which I currently do) or sort the errors out by adding a handling for a specific device?

3. For the switch to active I need an interrupt message for which I implemented snd_usb_interrupt_trans since I did not find any other convenience function to do this.