diff --git a/Documentation/devicetree/bindings/sound/gtm601.txt b/Documentation/devicetree/bindings/sound/gtm601.txt
index 5efc8c068de0..efa32a486c4a 100644
--- a/Documentation/devicetree/bindings/sound/gtm601.txt
+++ b/Documentation/devicetree/bindings/sound/gtm601.txt
@@ -1,10 +1,16 @@
 GTM601 UMTS modem audio interface CODEC
 
-This device has no configuration interface. Sample rate is fixed - 8kHz.
+This device has no configuration interface. The sample rate and channels are
+based on the compatible string
+	"option,gtm601" = 8kHz mono
+	"broadmobi,bm818" = 48KHz stereo
 
 Required properties:
 
-  - compatible : "option,gtm601"
+  - compatible : one of
+	"option,gtm601"
+	"broadmobi,bm818"
+
 
 Example: