i2c: soft_i2c: add simple GPIO implementation

Since the vast majority of GPIO I2C implementations behave the same way,
support the common GPIO framework with default settings.

This adds two new defines CONFIG_SOFT_I2C_GPIO_{SCL,SDA} so that boards
which want GPIO I2C support need only define these.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Tested-by: Thomas Chou <thomas@wytron.com.tw>

README

@@ -1495,6 +1495,16 @@ The following options need to be configured:
 
 		#define I2C_DELAY  udelay(2)
 
+		CONFIG_SOFT_I2C_GPIO_SCL / CONFIG_SOFT_I2C_GPIO_SDA
+
+		If your arch supports the generic GPIO framework (asm/gpio.h),
+		then you may alternatively define the two GPIOs that are to be
+		used as SCL / SDA.  Any of the previous I2C_xxx macros will
+		have GPIO-based defaults assigned to them as appropriate.
+
+		You should define these to the GPIO value as given directly to
+		the generic GPIO functions.
+
 		CONFIG_SYS_I2C_INIT_BOARD
 
 		When a board is reset during an i2c bus transfer

drivers/i2c/soft_i2c.c

@@ -51,6 +51,58 @@
 #endif
 #include <i2c.h>
 
+#if defined(CONFIG_SOFT_I2C_GPIO_SCL)
+# include <asm/gpio.h>
+
+# ifndef I2C_GPIO_SYNC
+#  define I2C_GPIO_SYNC
+# endif
+
+# ifndef I2C_INIT
+#  define I2C_INIT \
+	do { \
+		gpio_request(CONFIG_SOFT_I2C_GPIO_SCL, "soft_i2c"); \
+		gpio_request(CONFIG_SOFT_I2C_GPIO_SDA, "soft_i2c"); \
+	} while (0)
+# endif
+
+# ifndef I2C_ACTIVE
+#  define I2C_ACTIVE do { } while (0)
+# endif
+
+# ifndef I2C_TRISTATE
+#  define I2C_TRISTATE do { } while (0)
+# endif
+
+# ifndef I2C_READ
+#  define I2C_READ gpio_get_value(CONFIG_SOFT_I2C_GPIO_SDA)
+# endif
+
+# ifndef I2C_SDA
+#  define I2C_SDA(bit) \
+	do { \
+		if (bit) \
+			gpio_direction_input(CONFIG_SOFT_I2C_GPIO_SDA); \
+		else \
+			gpio_direction_output(CONFIG_SOFT_I2C_GPIO_SDA, 0); \
+		I2C_GPIO_SYNC; \
+	} while (0)
+# endif
+
+# ifndef I2C_SCL
+#  define I2C_SCL(bit) \
+	do { \
+		gpio_direction_output(CONFIG_SOFT_I2C_GPIO_SCL, bit); \
+		I2C_GPIO_SYNC; \
+	} while (0)
+# endif
+
+# ifndef I2C_DELAY
+#  define I2C_DELAY udelay(5)	/* 1/4 I2C clock duration */
+# endif
+
+#endif
+
 /* #define	DEBUG_I2C	*/
 
 #ifdef DEBUG_I2C