--- linux-4.9.37/drivers/usb/gadget/legacy/Kconfig	2017-07-12 16:42:41.000000000 +0300
+++ linux-4.9.y/drivers/usb/gadget/legacy/Kconfig	2021-06-07 13:01:34.000000000 +0300
@@ -56,6 +56,7 @@
 	select SND_PCM
 	select USB_F_UAC1 if GADGET_UAC1
 	select USB_F_UAC2 if !GADGET_UAC1
+	select USB_U_AUDIO if USB_F_UAC2
 	help
 	  This Gadget Audio driver is compatible with USB Audio Class
 	  specification 2.0. It implements 1 AudioControl interface,