From d8d0db7bb358ef65d60726a61bfcd08eccff0bc0 Mon Sep 17 00:00:00 2001
From: Tom Yan <tom.ty89@gmail.com>
Date: Tue, 18 Aug 2020 01:20:11 +0800
Subject: [PATCH] ALSA: usb-audio: ignore broken processing/extension unit
Git-commit: d8d0db7bb358ef65d60726a61bfcd08eccff0bc0
Patch-mainline: v5.9-rc2
References: git-fixes

Some devices have broken extension unit where getting current value
doesn't work. Attempt that once when creating mixer control for it. If
it fails, just ignore it, so that it won't cripple the device entirely
(and/or make the error floods).

Signed-off-by: Tom Yan <tom.ty89@gmail.com>
Link: https://lore.kernel.org/r/5f3abc52.1c69fb81.9cf2.fe91@mx.google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

---
 sound/usb/mixer.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -2382,7 +2382,7 @@ static int build_audio_procunit(struct m
 	int num_ins;
 	struct usb_mixer_elem_info *cval;
 	struct snd_kcontrol *kctl;
-	int i, err, nameid, type, len;
+	int i, err, nameid, type, len, val;
 	struct procunit_info *info;
 	struct procunit_value_info *valinfo;
 	const struct usbmix_name_map *map;
@@ -2485,6 +2485,12 @@ static int build_audio_procunit(struct m
 			break;
 		}
 
+		err = get_cur_ctl_value(cval, cval->control << 8, &val);
+		if (err < 0) {
+			usb_mixer_elem_info_free(cval);
+			return -EINVAL;
+		}
+
 		kctl = snd_ctl_new1(&mixer_procunit_ctl, cval);
 		if (!kctl) {
 			usb_mixer_elem_info_free(cval);