v4.19.13 snapshot.
diff --git a/sound/usb/debug.h b/sound/usb/debug.h
new file mode 100644
index 0000000..7dd983c
--- /dev/null
+++ b/sound/usb/debug.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __USBAUDIO_DEBUG_H
+#define __USBAUDIO_DEBUG_H
+
+/*
+ * h/w constraints
+ */
+
+#ifdef HW_CONST_DEBUG
+#define hwc_debug(fmt, args...) printk(KERN_DEBUG fmt, ##args)
+#else
+#define hwc_debug(fmt, args...) do { } while(0)
+#endif
+
+#endif /* __USBAUDIO_DEBUG_H */
+