I am trying to make a Focusrite Scarlett 18i20 (2nd Generation) work as a USB audio capture device with Linux.  Using the most current Linux kernel without change (v4.12-rc6), Mic inputs 1 and 2 are successfully captured.  However, no other inputs are heard.  The Scarlett device also presents a very limited set of ALSA controls.

exxothermic@exxothermic-BFC:~$ lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 002: ID 1235:8201 Focusrite-Novation
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
exxothermic@exxothermic-BFC:~$ amixer -c 1 contents
numid=3,iface=MIXER,name='ADAT Validity'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on
numid=4,iface=MIXER,name='Clock Source'
  ; type=ENUMERATED,access=rw------,values=1,items=3
  ; Item #0 'Internal'
  ; Item #1 'S/PDIF'
  ; Item #2 'ADAT'
  : values=0
numid=1,iface=MIXER,name='Internal Validity'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on
numid=2,iface=MIXER,name='S/PDIF Validity'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on

I modified sound/usb driver files mixer_quirks.c and mixer_scarlett.c to treat the Scarlett 2nd generation device the same way it handles the Scarlett 1st generation

0x1235:0x800c    1st Generation
0x1235:0x8201    2nd Generation

When checking with amixer, 228 controls are now listed, along with errors that prevent alsamixer from being used.  I have no information about how to properly configure these controls.

I am interested in any pointer to or information about how to configure and use this Scarlett 2nd Generation device.

Thank you,

Lloyd Dickman
lloyd@audioeverywhere.com