[RFC]sound:usb:mixer.c: Solving 'Generic AB13X USB Audio' Unlikely volume range.

[Sidharth Seela <sidharthseela@gmail.com>]

Dear Maintainers,
I am using a generic "boat" make earphones, which are too loud across
different systems with eg: iOS, macOS, Debian Linux. And hence I believe
the issue is not with a driver but the headphones.

After connecting this device to laptop I get the following in dmesg logs:
	usb 1-5: New USB device found, idVendor=001f, idProduct=0b21, bcdDevice= 1.00
	usb 1-5: New USB device strings: Mfr=1, Product=2, SerialNumber=3
	usb 1-5: Product: AB13X USB Audio
	usb 1-5: Manufacturer: Generic
	usb 1-5: SerialNumber: 20210726905926
	usb 1-5: Warning! Unlikely big volume range (=11520), cval->res is probably wrong.
	usb 1-5: [2] FU [PCM Playback Volume] ch = 2, val = -11520/0/1
	usb 1-5: Warning! Unlikely big volume range (=8191), cval->res is probably wrong.
	usb 1-5: [5] FU [Mic Capture Volume] ch = 1, val = 0/8191/1

By using pavucontrol, I am able to get fair sound, after reducing 17dB in
Analog Stereo Output and reducing 6dB in Digital Stereo Output.

I believe this issue could be solved by adding a quirk patch to
sound/usb/mixer.c:1096 (/* volume control quriks */).


BR,
Sidharth Seela