Merge pull request #1458 from DigitalDreamtimeLtd/rpi-4.4.y-iq_24db

Allow up to 24dB digital gain to be applied when using IQAudIO DAC (original DAC, not DAC+)

Author: pelwell

arch/arm/boot/dts/overlays/README

@@ -490,8 +490,21 @@ Params: <None>
 
 Name:   iqaudio-dac
 Info:   Configures the IQaudio DAC audio card
-Load:   dtoverlay=iqaudio-dac
-Params: <None>
+Load:   dtoverlay=iqaudio-dac,<param>
+Params: 24db_digital_gain       Allow gain to be applied via the PCM512x codec
+                                Digital volume control. Enable with
+                                "dtoverlay=iqaudio-dac,24db_digital_gain"
+                                (The default behaviour is that the Digital
+                                volume control is limited to a maximum of
+                                0dB. ie. it can attenuate but not provide
+                                gain. For most users, this will be desired
+                                as it will prevent clipping. By appending
+                                the 24db_digital_gain parameter, the Digital
+                                volume control will allow up to 24dB of
+                                gain. If this parameter is enabled, it is the
+                                responsibility of the user to ensure that
+                                the Digital volume control is set to a value
+                                that does not result in clipping/distortion!)
 
 
 Name:   iqaudio-dacplus

arch/arm/boot/dts/overlays/iqaudio-dac-overlay.dts

@@ -30,10 +30,14 @@
 
 	fragment@2 {
 		target = <&sound>;
-		__overlay__ {
+		frag2: __overlay__ {
 			compatible = "iqaudio,iqaudio-dac";
 			i2s-controller = <&i2s>;
 			status = "okay";
 		};
 	};
+
+	__overrides__ {
+		24db_digital_gain = <&frag2>,"iqaudio,24db_digital_gain?";
+	};
 };