[PATCH] ALSA: usb: mixer: volume quirk for ESS Technology Asus USB DAC

[Chris Chiu]

The Asus USB DAC is a USB type-C audio dongle for connecting to
the headset and headphone. The volume minimum value -23040 which
is 0xa600 in hexadecimal with the resolution value 1 indicates
this should be endianness issue caused by the firmware bug. Add
a volume quirk to fix the volume control problem.

Also fixes this warning:
  Warning! Unlikely big volume range (=23040), cval->res is probably wrong.
  [5] FU [Headset Capture Volume] ch = 1, val = -23040/0/1
  Warning! Unlikely big volume range (=23040), cval->res is probably wrong.
  [7] FU [Headset Playback Volume] ch = 1, val = -23040/0/1

Signed-off-by: Chris Chiu <chiu at endlessm.com>
---
 sound/usb/mixer.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 81b2db0edd5f..0b568a9fdab3 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1171,6 +1171,14 @@ static void volume_control_quirks(struct usb_mixer_elem_info *cval,
 			cval->res = 384;
 		}
 		break;
+	case USB_ID(0x0495, 0x3042): /* ESS Technology Asus USB DAC */
+		if ((strstr(kctl->id.name, "Playback Volume") != NULL) ||
+			strstr(kctl->id.name, "Capture Volume") != NULL) {
+			cval->min >>= 8;
+			cval->max = 0;
+			cval->res = 1;
+		}
+		break;
 	}
 }
 
-- 
2.20.1