[U-Boot] [PATCH v2 2/2] dm: i2c: implement gpio-based I2C deblock

[Alexander Kochetkov]

The commit implement a gpio-based software deblocking. The code
extract I2C pins description from device tree, switch pins to GPIO
mode, toggle SCL until slave release SDA, send I2C stop and switch
I2C pins back to I2C mode.

Signed-off-by: Alexander Kochetkov <al.kochet at gmail.com>
---
 drivers/i2c/i2c-uclass.c |  118 ++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 109 insertions(+), 9 deletions(-)

diff --git a/drivers/i2c/i2c-uclass.c b/drivers/i2c/i2c-uclass.c
index 920811a..4ac6ef8 100644
--- a/drivers/i2c/i2c-uclass.c
+++ b/drivers/i2c/i2c-uclass.c
@@ -11,9 +11,19 @@
 #include <malloc.h>
 #include <dm/device-internal.h>
 #include <dm/lists.h>
+#include <dm/pinctrl.h>
+#ifdef CONFIG_DM_GPIO
+#include <asm/gpio.h>
+#endif
 
 #define I2C_MAX_OFFSET_LEN	4
 
+enum {
+	PIN_SDA = 0,
+	PIN_SCL,
+	PIN_COUNT,
+};
+
 /* Useful debugging function */
 void i2c_dump_msgs(struct i2c_msg *msg, int nmsgs)
 {
@@ -445,20 +455,110 @@ int i2c_get_chip_offset_len(struct udevice *dev)
 	return chip->offset_len;
 }
 
+#ifdef CONFIG_DM_GPIO
+static void i2c_gpio_set_pin(struct gpio_desc *pin, int bit)
+{
+	if (bit)
+		dm_gpio_set_dir_flags(pin, GPIOD_IS_IN);
+	else
+		dm_gpio_set_dir_flags(pin, GPIOD_IS_OUT |
+					   GPIOD_ACTIVE_LOW |
+					   GPIOD_IS_OUT_ACTIVE);
+}
+
+static int i2c_gpio_get_pin(struct gpio_desc *pin)
+{
+	return dm_gpio_get_value(pin);
+}
+
+static int i2c_deblock_gpio_loop(struct gpio_desc *sda_pin,
+				 struct gpio_desc *scl_pin)
+{
+	int counter = 9;
+	int ret = 0;
+
+	i2c_gpio_set_pin(sda_pin, 1);
+	i2c_gpio_set_pin(scl_pin, 1);
+	udelay(5);
+
+	/*  Toggle SCL until slave release SDA */
+	while (counter-- >= 0) {
+		i2c_gpio_set_pin(scl_pin, 1);
+		udelay(5);
+		i2c_gpio_set_pin(scl_pin, 0);
+		udelay(5);
+		if (i2c_gpio_get_pin(sda_pin))
+			break;
+	}
+
+	/* Then, send I2C stop */
+	i2c_gpio_set_pin(sda_pin, 0);
+	udelay(5);
+
+	i2c_gpio_set_pin(scl_pin, 1);
+	udelay(5);
+
+	i2c_gpio_set_pin(sda_pin, 1);
+	udelay(5);
+
+	if (!i2c_gpio_get_pin(sda_pin) || !i2c_gpio_get_pin(scl_pin))
+		ret = -EREMOTEIO;
+
+	return ret;
+}
+
+static int i2c_deblock_gpio(struct udevice *bus)
+{
+	struct gpio_desc gpios[PIN_COUNT];
+	int ret, ret0;
+
+	ret = gpio_request_list_by_name(bus, "gpios", gpios,
+					ARRAY_SIZE(gpios), GPIOD_IS_IN);
+	if (ret != ARRAY_SIZE(gpios)) {
+		debug("%s: I2C Node '%s' has no 'gpios' property %s\n",
+		      __func__, dev_read_name(bus), bus->name);
+		if (ret >= 0) {
+			gpio_free_list(bus, gpios, ret);
+			ret = -ENOENT;
+		}
+		goto out;
+	}
+
+	ret = pinctrl_select_state(bus, "gpio");
+	if (ret) {
+		debug("%s: I2C Node '%s' has no 'gpio' pinctrl state. %s\n",
+		      __func__, dev_read_name(bus), bus->name);
+		goto out_no_pinctrl;
+	}
+
+	ret0 = i2c_deblock_gpio_loop(&gpios[PIN_SDA], &gpios[PIN_SCL]);
+
+	ret = pinctrl_select_state(bus, "default");
+	if (ret) {
+		debug("%s: I2C Node '%s' has no 'default' pinctrl state. %s\n",
+		      __func__, dev_read_name(bus), bus->name);
+	}
+
+	ret = !ret ? ret0 : ret;
+
+out_no_pinctrl:
+	gpio_free_list(bus, gpios, ARRAY_SIZE(gpios));
+out:
+	return ret;
+}
+#else
+static int i2c_deblock_gpio(struct udevice *bus)
+{
+	return -ENOSYS;
+}
+#endif // CONFIG_DM_GPIO
+
 int i2c_deblock(struct udevice *bus)
 {
 	struct dm_i2c_ops *ops = i2c_get_ops(bus);
 
-	/*
-	 * We could implement a software deblocking here if we could get
-	 * access to the GPIOs used by I2C, and switch them to GPIO mode
-	 * and then back to I2C. This is somewhat beyond our powers in
-	 * driver model at present, so for now just fail.
-	 *
-	 * See https://patchwork.ozlabs.org/patch/399040/
-	 */
 	if (!ops->deblock)
-		return -ENOSYS;
+		return i2c_deblock_gpio(bus);
 
 	return ops->deblock(bus);
 }
-- 
1.7.9.5