[FT C400, PATCH RFC, v3 4/9] usb-audio: skip UAC2 EFFECT_UNIT

[Eldad Zack <eldad@fogrefinery.com>]

Current code mishandles the case where the device is a UAC2
and the bDescriptorSubtype is a UAC2 Effect Unit (0x07).
It tries to parse it as a Processing Unit (which is similar to two
other UAC1 units with overlapping subtypes), but since the structure
is different (See: 4.7.2.10, 4.7.2.11 in UAC2 standard), the parsing
is done incorrectly and prevents the device from initializing.
For now, just ignore the unit.

Signed-off-by: Eldad Zack <eldad@fogrefinery.com>
---
 sound/usb/mixer.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index b0fc6ae..4eacbe2 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -723,8 +723,19 @@ static int check_input_term(struct mixer_build *state, int id, struct usb_audio_
 			return 0;
 		}
 		case UAC1_PROCESSING_UNIT:
-		case UAC1_EXTENSION_UNIT: {
+		case UAC1_EXTENSION_UNIT:
+		/* UAC2_PROCESSING_UNIT_V2 */
+		/* UAC2_EFFECT_UNIT */ {
 			struct uac_processing_unit_descriptor *d = p1;
+
+			if (state->mixer->protocol == UAC_VERSION_2 &&
+				hdr[2] == UAC2_EFFECT_UNIT) {
+				/* UAC2/UAC1 unit IDs overlap here in an
+				 * uncompatible way. Ignore this unit for now.
+				 */
+				return 0;
+			}
+
 			if (d->bNrInPins) {
 				id = d->baSourceID[0];
 				break; /* continue to parse */
-- 
1.7.8.6