Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/include/uapi/linux/usb/audio.h b/include/uapi/linux/usb/audio.h
index ddc5396..76b7c3f 100644
--- a/include/uapi/linux/usb/audio.h
+++ b/include/uapi/linux/usb/audio.h
@@ -450,6 +450,43 @@
 	}
 }
 
+/*
+ * Extension Unit (XU) has almost compatible layout with Processing Unit, but
+ * on UAC2, it has a different bmControls size (bControlSize); it's 1 byte for
+ * XU while 2 bytes for PU.  The last iExtension field is a one-byte index as
+ * well as iProcessing field of PU.
+ */
+static inline __u8 uac_extension_unit_bControlSize(struct uac_processing_unit_descriptor *desc,
+						   int protocol)
+{
+	switch (protocol) {
+	case UAC_VERSION_1:
+		return desc->baSourceID[desc->bNrInPins + 4];
+	case UAC_VERSION_2:
+		return 1; /* in UAC2, this value is constant */
+	case UAC_VERSION_3:
+		return 4; /* in UAC3, this value is constant */
+	default:
+		return 1;
+	}
+}
+
+static inline __u8 uac_extension_unit_iExtension(struct uac_processing_unit_descriptor *desc,
+						 int protocol)
+{
+	__u8 control_size = uac_extension_unit_bControlSize(desc, protocol);
+
+	switch (protocol) {
+	case UAC_VERSION_1:
+	case UAC_VERSION_2:
+	default:
+		return *(uac_processing_unit_bmControls(desc, protocol)
+			 + control_size);
+	case UAC_VERSION_3:
+		return 0; /* UAC3 does not have this field */
+	}
+}
+
 /* 4.5.2 Class-Specific AS Interface Descriptor */
 struct uac1_as_header_descriptor {
 	__u8  bLength;			/* in bytes: 7 */