hwmon: (ads1015) Make gain and datarate configurable

Configuration for ads1015 gain and datarate is possible via
devicetree or platform data.

This is a followup patch to previous ads1015 patches on Jean Delvares
tree.

Signed-off-by: Dirk Eibach <eibach@gdsys.de>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

Documentation/devicetree/bindings/hwmon/ads1015.txt

@@ -5,25 +5,69 @@ This device is a 12-bit A-D converter with 4 inputs.
 The inputs can be used single ended or in certain differential combinations.
 
 For configuration all possible combinations are mapped to 8 channels:
-0: Voltage over AIN0 and AIN1.
-1: Voltage over AIN0 and AIN3.
-2: Voltage over AIN1 and AIN3.
-3: Voltage over AIN2 and AIN3.
-4: Voltage over AIN0 and GND.
-5: Voltage over AIN1 and GND.
-6: Voltage over AIN2 and GND.
-7: Voltage over AIN3 and GND.
+  0: Voltage over AIN0 and AIN1.
+  1: Voltage over AIN0 and AIN3.
+  2: Voltage over AIN1 and AIN3.
+  3: Voltage over AIN2 and AIN3.
+  4: Voltage over AIN0 and GND.
+  5: Voltage over AIN1 and GND.
+  6: Voltage over AIN2 and GND.
+  7: Voltage over AIN3 and GND.
 
-Optional properties:
+Each channel can be configured individually:
+ - pga is the programmable gain amplifier (values are full scale)
+    0: +/- 6.144 V
+    1: +/- 4.096 V
+    2: +/- 2.048 V (default)
+    3: +/- 1.024 V
+    4: +/- 0.512 V
+    5: +/- 0.256 V
+ - data_rate in samples per second
+    0: 128
+    1: 250
+    2: 490
+    3: 920
+    4: 1600 (default)
+    5: 2400
+    6: 3300
 
- - exported-channels : exported_channels is a bitmask that specifies which
-		       channels should be accessable by the user.
+1) The /ads1015 node
 
-Example:
-ads1015@49 {
-	compatible = "ti,ads1015";
-	reg = <0x49>;
-	exported-channels = <0x14>;
-};
+  Required properties:
 
-In this example only channel 2 and 4 would be accessable by the user.
+   - compatible : must be "ti,ads1015"
+   - reg : I2C bus address of the device
+   - #address-cells : must be <1>
+   - #size-cells : must be <0>
+
+  The node contains child nodes for each channel that the platform uses.
+
+  Example ADS1015 node:
+
+    ads1015@49 {
+	    compatible = "ti,ads1015";
+	    reg = <0x49>;
+	    #address-cells = <1>;
+	    #size-cells = <0>;
+
+	    [ child node definitions... ]
+    }
+
+2) channel nodes
+
+  Required properties:
+
+   - reg : the channel number
+
+  Optional properties:
+
+   - ti,gain : the programmable gain amplifier setting
+   - ti,datarate : the converter data rate
+
+  Example ADS1015 channel node:
+
+    channel@4 {
+	    reg = <4>;
+	    ti,gain = <3>;
+	    ti,datarate = <5>;
+    };