[018/121] ALSA: usb-audio: skip UAC2 EFFECT_UNIT

[Ben Hutchings]

3.2.51-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eldad Zack <eldad@xxxxxxxxxxxxxxx>

commit 5dae5fd24071319bb67d3375217d5b0b6d16cb0b upstream.

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@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 sound/usb/mixer.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -720,8 +720,19 @@ static int check_input_term(struct mixer
 			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 */

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