DT: Add overlays to configure I2C pins

Lifted from
https://www.raspberrypi.org/forums/viewtopic.php?f=107&t=120938&p=825883
so not claiming this to be my own work.
Adds overlays i2c0-bcm2708 and i2c1-bcm2708 that allow the pin
allocations for i2c-0 and i2c-1 to be changed.

Author: 6by9

arch/arm/boot/dts/overlays/Makefile

@@ -29,6 +29,8 @@ dtb-$(RPI_DT_OVERLAYS) += hy28a-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += hy28b-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += i2c-rtc-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += i2c-gpio-overlay.dtb
+dtb-$(RPI_DT_OVERLAYS) += i2c0-bcm2708-overlay.dtb
+dtb-$(RPI_DT_OVERLAYS) += i2c1-bcm2708-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += i2s-mmap-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += iqaudio-dac-overlay.dtb
 dtb-$(RPI_DT_OVERLAYS) += iqaudio-dacplus-overlay.dtb

arch/arm/boot/dts/overlays/README

@@ -371,6 +371,22 @@ Params: ds1307                  Select the DS1307 device
         pcf8563                 Select the PCF8563 device
 
 
+Name:   i2c0-bcm2708
+Info:   Enable the i2c_bcm2708 driver for the i2c0 bus
+Load:   dtoverlay=i2c0-bcm2708,<param>=<val>
+Params: sda0_pin                GPIO pin for SDA0 (0, 28 [or 44] - default 0)
+        scl0_pin                GPIO pin for SCL0 (1, 29 [or 45] - default 1)
+
+
+Name:   i2c1-bcm2708
+Info:   Enable the i2c_bcm2708 driver for the i2c1 bus
+Load:   dtoverlay=i2c1-bcm2708,<param>=<val>
+Params: sda1_pin                GPIO pin for SDA1 (2 or 44 - default 2)
+        scl1_pin                GPIO pin for SCL1 (3 or 45 - default 3)
+        pin_func                Alternative pin function (4 (alt0), 6 (alt2) -
+                                default 4)
+
+
 Name:   i2s-mmap
 Info:   Enables mmap support in the bcm2708-i2s driver
 Load:   dtoverlay=i2s-mmap

arch/arm/boot/dts/overlays/i2c0-bcm2708-overlay.dts

@@ -0,0 +1,36 @@
+/*
+ * Device tree overlay for i2c_bcm2708, i2c0 bus
+ *
+ * Compile:
+ * dtc -@ -I dts -O dtb -o i2c0-bcm2708-overlay.dtb i2c0-bcm2708-overlay.dts
+ */
+
+/dts-v1/;
+/plugin/;
+
+/{
+   compatible = "brcm,bcm2708";
+
+   fragment@0 {
+      target = <&i2c0>;
+      __overlay__ {
+         pinctrl-0 = <&i2c0_pins>;
+         status = "okay";
+      };
+   };
+
+   fragment@1 {
+      target = <&gpio>;
+      __overlay__ {
+         i2c0_pins: i2c0 {
+            brcm,pins = <0 1>;
+            brcm,function = <4>; /* alt0 */
+         };
+      };
+   };
+
+   __overrides__ {
+      sda0_pin = <&i2c0_pins>,"brcm,pins:0";
+      scl0_pin = <&i2c0_pins>,"brcm,pins:4";
+   };
+};

arch/arm/boot/dts/overlays/i2c1-bcm2708-overlay.dts

@@ -0,0 +1,37 @@
+/*
+ * Device tree overlay for i2c_bcm2708, i2c1 bus
+ *
+ * Compile:
+ * dtc -@ -I dts -O dtb -o i2c1-bcm2708-overlay.dtb i2c1-bcm2708-overlay.dts
+ */
+
+/dts-v1/;
+/plugin/;
+
+/{
+   compatible = "brcm,bcm2708";
+
+   fragment@0 {
+      target = <&i2c1>;
+      __overlay__ {
+         pinctrl-0 = <&i2c1_pins>;
+         status = "okay";
+      };
+   };
+
+   fragment@1 {
+      target = <&gpio>;
+      __overlay__ {
+         i2c1_pins: i2c1 {
+            brcm,pins = <2 3>;
+            brcm,function = <4>; /* alt0 */
+         };
+      };
+   };
+
+   __overrides__ {
+      sda1_pin = <&i2c1_pins>,"brcm,pins:0";
+      scl1_pin = <&i2c1_pins>,"brcm,pins:4";
+      pin_func = <&i2c1_pins>,"brcm,function:0";
+   };
+};