iio: xoadc: augment DT bindings a bit

In order to accommodate in a logical manner for the premuxed channels
in PM8921 and the similarly addressed channels in later PMICs, we
need a twocell arrangement with premux and analog mux setting as
a tuple to uniquely identify a hardware channel.

These bindings are not yet in use, so it should be fine to augment
them before we actually start using it in drivers and device trees.

This scheme came out of lengthy discussions and reverse-engineering
and reading of the few information sources we have.

Cc: devicetree@vger.kernel.org
Acked-by: Rob Herring <robh+dt@kernel.org>
Suggested-by: Björn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/qcom,pm8xxx-xoadc.txt

@@ -19,46 +19,56 @@ Required properties:
   with PMIC variant but is typically something like 2.2 or 1.8V.
 
 The following required properties are standard for IO channels, see
-iio-bindings.txt for more details:
+iio-bindings.txt for more details, but notice that this particular
+ADC has a special addressing scheme that require two cells for
+identifying each ADC channel:
 
-- #address-cells: should be set to <1>
+- #address-cells: should be set to <2>, the first cell is the
+  prescaler (on PM8058) or premux (on PM8921) with two valid bits
+  so legal values are 0x00, 0x01 or 0x02. The second cell
+  is the main analog mux setting (0x00..0x0f). The combination
+  of prescaler/premux and analog mux uniquely addresses a hardware
+  channel on all systems.
 
 - #size-cells: should be set to <0>
 
-- #io-channel-cells: should be set to <1>
+- #io-channel-cells: should be set to <2>, again the cells are
+  precaler or premux followed by the analog muxing line.
 
 - interrupts: should refer to the parent PMIC interrupt controller
   and reference the proper ADC interrupt.
 
 Required subnodes:
 
-The ADC channels are configured as subnodes of the ADC. Since some of
-them are used for calibrating the ADC, these nodes are compulsory:
+The ADC channels are configured as subnodes of the ADC.
+
+Since some of them are used for calibrating the ADC, these nodes are
+compulsory:
 
 adc-channel@c {
-	reg = <0x0c>;
+	reg = <0x00 0x0c>;
 };
 
 adc-channel@d {
-	reg = <0x0d>;
+	reg = <0x00 0x0d>;
 };
 
 adc-channel@f {
-	reg = <0x0f>;
+	reg = <0x00 0x0f>;
 };
 
 These three nodes are used for absolute and ratiometric calibration
 and only need to have these reg values: they are by hardware definition
 1:1 ratio converters that sample 625, 1250 and 0 milliV and create
 an interpolation calibration for all other ADCs.
 
-Optional subnodes: any channels other than channel 0x0c, 0x0d and
-0x0f are optional.
+Optional subnodes: any channels other than channels [0x00 0x0c],
+[0x00 0x0d] and [0x00 0x0f] are optional.
 
 Required channel node properties:
 
 - reg: should contain the hardware channel number in the range
-  0 .. 0x0f (4 bits). The hardware only supports 16 channels.
+  0 .. 0xff (8 bits).
 
 Optional channel node properties:
 
@@ -94,56 +104,54 @@ Example:
 xoadc: xoadc@197 {
 	compatible = "qcom,pm8058-adc";
 	reg = <0x197>;
-	interrupt-parent = <&pm8058>;
-	interrupts = <76 1>;
-	#address-cells = <1>;
+	interrupts-extended = <&pm8058 76 IRQ_TYPE_EDGE_RISING>;
+	#address-cells = <2>;
 	#size-cells = <0>;
-	#io-channel-cells = <1>;
+	#io-channel-cells = <2>;
 
 	vcoin: adc-channel@0 {
-		reg = <0x00>;
+		reg = <0x00 0x00>;
 	};
 	vbat: adc-channel@1 {
-		reg = <0x01>;
+		reg = <0x00 0x01>;
 	};
 	dcin: adc-channel@2 {
-		reg = <0x02>;
+		reg = <0x00 0x02>;
 	};
 	ichg: adc-channel@3 {
-		reg = <0x03>;
+		reg = <0x00 0x03>;
 	};
 	vph_pwr: adc-channel@4 {
-		reg = <0x04>;
+		reg = <0x00 0x04>;
 	};
 	usb_vbus: adc-channel@a {
-		reg = <0x0a>;
+		reg = <0x00 0x0a>;
 	};
 	die_temp: adc-channel@b {
-		reg = <0x0b>;
+		reg = <0x00 0x0b>;
 	};
 	ref_625mv: adc-channel@c {
-		reg = <0x0c>;
+		reg = <0x00 0x0c>;
 	};
 	ref_1250mv: adc-channel@d {
-		reg = <0x0d>;
+		reg = <0x00 0x0d>;
 	};
 	ref_325mv: adc-channel@e {
-		reg = <0x0e>;
+		reg = <0x00 0x0e>;
 	};
 	ref_muxoff: adc-channel@f {
-		reg = <0x0f>;
+		reg = <0x00 0x0f>;
 	};
 };
 
-
 /* IIO client node */
 iio-hwmon {
 	compatible = "iio-hwmon";
-	io-channels = <&xoadc 0x01>, /* Battery */
-		    <&xoadc 0x02>, /* DC in (charger) */
-		    <&xoadc 0x04>, /* VPH the main system voltage */
-		    <&xoadc 0x0b>, /* Die temperature */
-		    <&xoadc 0x0c>, /* Reference voltage 1.25V */
-		    <&xoadc 0x0d>, /* Reference voltage 0.625V */
-		    <&xoadc 0x0e>; /* Reference voltage 0.325V */
+	io-channels = <&xoadc 0x00 0x01>, /* Battery */
+		    <&xoadc 0x00 0x02>, /* DC in (charger) */
+		    <&xoadc 0x00 0x04>, /* VPH the main system voltage */
+		    <&xoadc 0x00 0x0b>, /* Die temperature */
+		    <&xoadc 0x00 0x0c>, /* Reference voltage 1.25V */
+		    <&xoadc 0x00 0x0d>, /* Reference voltage 0.625V */
+		    <&xoadc 0x00 0x0e>; /* Reference voltage 0.325V */
 };