drivers: i2c: Add support for clock stretching in the i2c-gpio module.

Some I2C peripherals like TI charger or gauge chips need support for I2C
clock stretching. This patch includes that and makes these modules
usable with I2C emulation over GPIO.

Signed-off-by: Bas van Loon <bas@arch-embedded.com>

Author: bas-archembedded

drivers/i2c/Kconfig.gpio

@@ -8,3 +8,19 @@ config I2C_GPIO
 	select I2C_BITBANG
 	help
 	  Enable software driven (bit banging) I2C support using GPIO pins
+
+if I2C_GPIO
+
+config I2C_GPIO_CLOCK_STRETCHING
+	bool "GPIO bit banging I2C clock stretching support"
+	default y
+	help
+	  Enable Slave clock stretching support
+
+config I2C_GPIO_CLOCK_STRETCHING_TIMEOUT_US
+	int "GPIO bit banging I2C clock stretching timeout (us)"
+	default 100000
+	help
+	  Timeout for clock stretching in microseconds.
+
+endif # I2C_GPIO

drivers/i2c/i2c_bitbang.c

@@ -20,6 +20,7 @@
 #include <errno.h>
 #include <zephyr/kernel.h>
 #include <zephyr/drivers/i2c.h>
+#include <zephyr/sys/util.h>
 #include "i2c_bitbang.h"
 
 /*
@@ -79,6 +80,14 @@ int i2c_bitbang_get_config(struct i2c_bitbang *context, uint32_t *config)
 static void i2c_set_scl(struct i2c_bitbang *context, int state)
 {
 	context->io->set_scl(context->io_context, state);
+#ifdef CONFIG_I2C_GPIO_CLOCK_STRETCHING
+	if (state == 1) {
+		/* Wait for slave to release the clock */
+		WAIT_FOR(context->io->get_scl(context->io_context) != 0,
+			 CONFIG_I2C_GPIO_CLOCK_STRETCHING_TIMEOUT_US,
+			 ;);
+	}
+#endif
 }
 
 static void i2c_set_sda(struct i2c_bitbang *context, int state)

drivers/i2c/i2c_bitbang.h

@@ -12,6 +12,10 @@
 struct i2c_bitbang_io {
 	/* Set the state of the SCL line (zero/non-zero value) */
 	void (*set_scl)(void *io_context, int state);
+#ifdef CONFIG_I2C_GPIO_CLOCK_STRETCHING
+	/* Return the state of the SCL line (zero/non-zero value) */
+	int (*get_scl)(void *io_context);
+#endif
 	/* Set the state of the SDA line (zero/non-zero value) */
 	void (*set_sda)(void *io_context, int state);
 	/* Return the state of the SDA line (zero/non-zero value) */

drivers/i2c/i2c_gpio.c

@@ -57,6 +57,16 @@ static void i2c_gpio_set_scl(void *io_context, int state)
 	gpio_pin_set_dt(&config->scl_gpio, state);
 }
 
+#ifdef CONFIG_I2C_GPIO_CLOCK_STRETCHING
+static int i2c_gpio_get_scl(void *io_context)
+{
+	const struct i2c_gpio_config *config = io_context;
+	int rc = gpio_pin_get_dt(&config->scl_gpio);
+
+	return rc != 0;
+}
+#endif
+
 static void i2c_gpio_set_sda(void *io_context, int state)
 {
 	const struct i2c_gpio_config *config = io_context;
@@ -75,6 +85,9 @@ static int i2c_gpio_get_sda(void *io_context)
 
 static const struct i2c_bitbang_io io_fns = {
 	.set_scl = &i2c_gpio_set_scl,
+#ifdef CONFIG_I2C_GPIO_CLOCK_STRETCHING
+	.get_scl = &i2c_gpio_get_scl,
+#endif
 	.set_sda = &i2c_gpio_set_sda,
 	.get_sda = &i2c_gpio_get_sda,
 };
@@ -162,7 +175,14 @@ static int i2c_gpio_init(const struct device *dev)
 		return -ENODEV;
 	}
 
+#ifdef CONFIG_I2C_GPIO_CLOCK_STRETCHING
+	err = gpio_pin_configure_dt(&config->scl_gpio, GPIO_INPUT | GPIO_OUTPUT_HIGH);
+	if (err == -ENOTSUP) {
+		err = gpio_pin_configure_dt(&config->scl_gpio, GPIO_OUTPUT_HIGH);
+	}
+#else
 	err = gpio_pin_configure_dt(&config->scl_gpio, GPIO_OUTPUT_HIGH);
+#endif
 	if (err) {
 		LOG_ERR("failed to configure SCL GPIO pin (err %d)", err);
 		return err;