dm: i2c: add i2c-gpio driver

This commit adds driver model support to software emulated i2c bus driver.
This driver supports kernel-style device tree bindings. Fdt properties in use:
- compatible - "i2c-gpio"
- gpios      - data and clock GPIO pin phandles
- delay-us   - micro seconds delay between GPIOs toggle operations,
               which is 1/4 of I2C speed clock period.

Added:
- Config: CONFIG_DM_I2C_GPIO
- File: drivers/i2c/i2c-gpio.c
- File: doc/device-tree-bindings/i2c/i2c-gpio.txt

Driver base code is taken from: drivers/i2c/soft-i2c.c, changes:
- use "i2c-gpio" naming
- update comments style
- move preprocesor macros into functions
- add device tree support
- add driver model i2c support
- code cleanup,
- add Kconfig entry

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Added braces in i2c_gpio_xfer() to fix style nit:
Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/doc/device-tree-bindings/i2c/i2c-gpio.txt b/doc/device-tree-bindings/i2c/i2c-gpio.txt
new file mode 100644
index 0000000000..ba56ed5dea
--- /dev/null
+++ b/doc/device-tree-bindings/i2c/i2c-gpio.txt
@@ -0,0 +1,37 @@
+I2C gpio device binding
+=======================
+
+Driver:
+- drivers/i2c/i2c-gpio.c
+
+Software i2c device-tree node properties:
+Required:
+* #address-cells = <1>;
+* #size-cells = <0>;
+* compatible = "i2c-gpio";
+* gpios = <sda ...>, <scl ...>;
+
+Optional:
+* i2c-gpio,delay-us = <5>;
+   The resulting transfer speed can be adjusted by setting the delay[us]
+   between gpio-toggle operations. Speed [Hz] = 1000000 / 4 * udelay[us],
+   It not defined, then default is 5us (~50KHz).
+
+Example:
+
+i2c-gpio@1 {
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	compatible = "i2c-gpio";
+	gpios = <&gpd1 0 GPIO_ACTIVE_HIGH>, /* SDA */
+		<&gpd1 1 GPIO_ACTIVE_HIGH>; /* CLK */
+
+	i2c-gpio,delay-us = <5>;
+
+	some_device@5 {
+		compatible = "some_device";
+		reg = <0x5>;
+		...
+	};
+};