From 1d8d6428d1da642ddd75b0be2d1bb1123ff8e017 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Tue, 24 Apr 2018 11:11:48 +0200
Subject: [PATCH] ALSA: usb-audio: Skip broken EU on Dell dock USB-audio
References: bsc#1090658
Git-commit: 1d8d6428d1da642ddd75b0be2d1bb1123ff8e017
Patch-mainline: v4.17-rc3

The Dell Dock USB-audio device with 0bda:4014 is behaving notoriously
bad, and we have already applied some workaround to avoid the firmware
hiccup.  Yet we still need to skip one thing, the Extension Unit at ID
4, which doesn't react correctly to the mixer ctl access.

Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1090658
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

---
 sound/usb/mixer_maps.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/sound/usb/mixer_maps.c
+++ b/sound/usb/mixer_maps.c
@@ -353,8 +353,11 @@ static struct usbmix_name_map bose_compa
 /*
  * Dell usb dock with ALC4020 codec had a firmware problem where it got
  * screwed up when zero volume is passed; just skip it as a workaround
+ *
+ * Also the extension unit gives an access error, so skip it as well.
  */
 static const struct usbmix_name_map dell_alc4020_map[] = {
+	{ 4, NULL },	/* extension unit */
 	{ 16, NULL },
 	{ 19, NULL },
 	{ 0 }