Build i2c_gpio module and add a device tree overlay to configure it.

Author: ali1234

arch/arm/boot/dts/overlays/Makefile

@@ -25,6 +25,7 @@ dtb-$(RPI_DT_OVERLAYS) += hifiberry-digi-overlay.dtb
 dtb-$(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) += 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

@@ -284,6 +284,17 @@ Params: speed                    Display SPI bus speed
         ledgpio                  GPIO used to control backlight
 
 
+Name:   i2c-gpio
+Info:   Adds support for software i2c controller on gpio pins
+Load:   dtoverlay=i2c-gpio,<param>
+Params: i2c_gpio_sda             GPIO used for I2C data (default "23")
+
+        i2c_gpio_scl             GPIO used for I2C clock (default "24")
+
+        i2c_gpio_delay_us        Clock delay in microseconds
+                                 (default "2" = ~100kHz)
+
+
 Name:   i2c-rtc
 Info:   Adds support for a number of I2C Real Time Clock devices
 Load:   dtoverlay=i2c-rtc,<param>

arch/arm/boot/dts/overlays/i2c-gpio-overlay.dts

@@ -0,0 +1,28 @@
+// Overlay for i2c_gpio bitbanging host bus.
+/dts-v1/;
+/plugin/;
+
+/ {
+	compatible = "brcm,bcm2708";
+
+	fragment@0 {
+		target-path = "/";
+		__overlay__ {
+			i2c_gpio: i2c@0 {
+				compatible = "i2c-gpio";
+				gpios = <&gpio 23 0 /* sda */
+					 &gpio 24 0 /* scl */
+					>;
+				i2c-gpio,delay-us = <2>;        /* ~100 kHz */
+				#address-cells = <1>;
+				#size-cells = <0>;
+			};
+		};
+	};
+	__overrides__ {
+		i2c_gpio_sda = <&i2c_gpio>,"gpios:4";
+		i2c_gpio_scl = <&i2c_gpio>,"gpios:16";
+		i2c_gpio_delay_us = <&i2c_gpio>,"i2c-gpio,delay-us:0";
+	};
+};
+

arch/arm/configs/bcm2709_defconfig

@@ -595,6 +595,7 @@ CONFIG_BCM_VC_SM=y
 CONFIG_I2C=y
 CONFIG_I2C_CHARDEV=m
 CONFIG_I2C_BCM2708=m
+CONFIG_I2C_GPIO=m
 CONFIG_SPI=y
 CONFIG_SPI_BCM2835=m
 CONFIG_SPI_BCM2708=m

arch/arm/configs/bcmrpi_defconfig

@@ -588,6 +588,7 @@ CONFIG_BCM_VC_SM=y
 CONFIG_I2C=y
 CONFIG_I2C_CHARDEV=m
 CONFIG_I2C_BCM2708=m
+CONFIG_I2C_GPIO=m
 CONFIG_SPI=y
 CONFIG_SPI_BCM2835=m
 CONFIG_SPI_BCM2708=m