Index: firmware/drivers/audio/wm8975.c
===================================================================
--- firmware/drivers/audio/wm8975.c	(revision 28315)
+++ firmware/drivers/audio/wm8975.c	(working copy)
@@ -319,6 +319,22 @@
 
 void audiohw_set_monitor(bool enable)
 {
-    (void)enable;
+    if (enable) {
+        // set volume to 0 dB
+        wm8975_regs[LOUTMIX1] &= ~LOUTMIX1_LI2LOVOL_MASK;
+        wm8975_regs[LOUTMIX1] |= LOUTMIX1_LI2LOVOL(2);
+        wm8975_regs[ROUTMIX2] &= ~ROUTMIX2_RI2ROVOL_MASK;
+        wm8975_regs[ROUTMIX2] |= ROUTMIX2_RI2ROVOL(2);
+        // set mux to line input
+        wm8975_write_and(LOUTMIX1, ~7);
+        wm8975_write_and(ROUTMIX1, ~7);
+        // enable bypass
+        wm8975_write_or(LOUTMIX1, LOUTMIX1_LI2LO);
+        wm8975_write_or(ROUTMIX2, ROUTMIX2_RI2RO);
+    } else {
+        // disable bypass
+        wm8975_write_and(LOUTMIX1, ~LOUTMIX1_LI2LO);
+        wm8975_write_and(ROUTMIX2, ~ROUTMIX2_RI2RO);
+    }
 }
 #endif /* HAVE_RECORDING */