diff --git a/sound/usb/card.c b/sound/usb/card.c
index b443a33..32e4be8 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -216,6 +216,11 @@
 	}
 
 	switch (protocol) {
+	default:
+		snd_printdd(KERN_WARNING "unknown interface protocol %#02x, assuming v1\n",
+			    protocol);
+		/* fall through */
+
 	case UAC_VERSION_1: {
 		struct uac1_ac_header_descriptor *h1 = control_header;
 
@@ -253,10 +258,6 @@
 
 		break;
 	}
-
-	default:
-		snd_printk(KERN_ERR "unknown protocol version 0x%02x\n", protocol);
-		return -EINVAL;
 	}
 
 	return 0;
diff --git a/sound/usb/clock.c b/sound/usb/clock.c
index b853f8d..7754a10 100644
--- a/sound/usb/clock.c
+++ b/sound/usb/clock.c
@@ -295,12 +295,11 @@
 
 	switch (altsd->bInterfaceProtocol) {
 	case UAC_VERSION_1:
+	default:
 		return set_sample_rate_v1(chip, iface, alts, fmt, rate);
 
 	case UAC_VERSION_2:
 		return set_sample_rate_v2(chip, iface, alts, fmt, rate);
 	}
-
-	return -EINVAL;
 }
 
diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 1a701f1..ef0a07e 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -275,6 +275,12 @@
 
 		/* get audio formats */
 		switch (protocol) {
+		default:
+			snd_printdd(KERN_WARNING "%d:%u:%d: unknown interface protocol %#02x, assuming v1\n",
+				    dev->devnum, iface_no, altno, protocol);
+			protocol = UAC_VERSION_1;
+			/* fall through */
+
 		case UAC_VERSION_1: {
 			struct uac1_as_header_descriptor *as =
 				snd_usb_find_csint_desc(alts->extra, alts->extralen, NULL, UAC_AS_GENERAL);
@@ -336,11 +342,6 @@
 				   dev->devnum, iface_no, altno, as->bTerminalLink);
 			continue;
 		}
-
-		default:
-			snd_printk(KERN_ERR "%d:%u:%d : unknown interface protocol %04x\n",
-				   dev->devnum, iface_no, altno, protocol);
-			continue;
 		}
 
 		/* get format type */
diff --git a/sound/usb/format.c b/sound/usb/format.c
index 3a13754..6914821 100644
--- a/sound/usb/format.c
+++ b/sound/usb/format.c
@@ -49,7 +49,8 @@
 	u64 pcm_formats;
 
 	switch (protocol) {
-	case UAC_VERSION_1: {
+	case UAC_VERSION_1:
+	default: {
 		struct uac_format_type_i_discrete_descriptor *fmt = _fmt;
 		sample_width = fmt->bBitResolution;
 		sample_bytes = fmt->bSubframeSize;
@@ -64,9 +65,6 @@
 		format <<= 1;
 		break;
 	}
-
-	default:
-		return -EINVAL;
 	}
 
 	pcm_formats = 0;
@@ -384,6 +382,10 @@
 	 * audio class v2 uses class specific EP0 range requests for that.
 	 */
 	switch (protocol) {
+	default:
+		snd_printdd(KERN_WARNING "%d:%u:%d : invalid protocol version %d, assuming v1\n",
+			   chip->dev->devnum, fp->iface, fp->altsetting, protocol);
+		/* fall through */
 	case UAC_VERSION_1:
 		fp->channels = fmt->bNrChannels;
 		ret = parse_audio_format_rates_v1(chip, fp, (unsigned char *) fmt, 7);
@@ -392,10 +394,6 @@
 		/* fp->channels is already set in this case */
 		ret = parse_audio_format_rates_v2(chip, fp);
 		break;
-	default:
-		snd_printk(KERN_ERR "%d:%u:%d : invalid protocol version %d\n",
-			   chip->dev->devnum, fp->iface, fp->altsetting, protocol);
-		return -EINVAL;
 	}
 
 	if (fp->channels < 1) {
@@ -438,6 +436,10 @@
 	fp->channels = 1;
 
 	switch (protocol) {
+	default:
+		snd_printdd(KERN_WARNING "%d:%u:%d : invalid protocol version %d, assuming v1\n",
+			   chip->dev->devnum, fp->iface, fp->altsetting, protocol);
+		/* fall through */
 	case UAC_VERSION_1: {
 		struct uac_format_type_ii_discrete_descriptor *fmt = _fmt;
 		brate = le16_to_cpu(fmt->wMaxBitRate);
@@ -456,10 +458,6 @@
 		ret = parse_audio_format_rates_v2(chip, fp);
 		break;
 	}
-	default:
-		snd_printk(KERN_ERR "%d:%u:%d : invalid protocol version %d\n",
-			   chip->dev->devnum, fp->iface, fp->altsetting, protocol);
-		return -EINVAL;
 	}
 
 	return ret;
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index c166db0..3ed3901 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -2175,7 +2175,15 @@
 	}
 
 	host_iface = &usb_ifnum_to_if(chip->dev, ctrlif)->altsetting[0];
-	mixer->protocol = get_iface_desc(host_iface)->bInterfaceProtocol;
+	switch (get_iface_desc(host_iface)->bInterfaceProtocol) {
+	case UAC_VERSION_1:
+	default:
+		mixer->protocol = UAC_VERSION_1;
+		break;
+	case UAC_VERSION_2:
+		mixer->protocol = UAC_VERSION_2;
+		break;
+	}
 
 	if ((err = snd_usb_mixer_controls(mixer)) < 0 ||
 	    (err = snd_usb_mixer_status_create(mixer)) < 0)
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 3634ced..3b5135c 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -173,13 +173,12 @@
 
 	switch (altsd->bInterfaceProtocol) {
 	case UAC_VERSION_1:
+	default:
 		return init_pitch_v1(chip, iface, alts, fmt);
 
 	case UAC_VERSION_2:
 		return init_pitch_v2(chip, iface, alts, fmt);
 	}
-
-	return -EINVAL;
 }
 
 /*