[PATCH] i2c: gpio: Add custom deblock sequence

[Marek Vasut]

Add custom deblock dequence for the I2C bus, needed on some devices.
This sequence is issued once, when probing the driver, and is controlled
by DT property, "i2c-gpio,deblock".

Signed-off-by: Marek Vasut <marex at denx.de>
---
 drivers/i2c/i2c-gpio.c | 67 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)

diff --git a/drivers/i2c/i2c-gpio.c b/drivers/i2c/i2c-gpio.c
index 4e8fa21473..46975ef5c8 100644
--- a/drivers/i2c/i2c-gpio.c
+++ b/drivers/i2c/i2c-gpio.c
@@ -39,6 +39,11 @@ static int i2c_gpio_sda_get(struct gpio_desc *sda)
 	return dm_gpio_get_value(sda);
 }
 
+static int i2c_gpio_scl_get(struct gpio_desc *scl)
+{
+	return dm_gpio_get_value(scl);
+}
+
 static void i2c_gpio_sda_set(struct gpio_desc *sda, int bit)
 {
 	if (bit)
@@ -305,6 +310,67 @@ static int i2c_gpio_set_bus_speed(struct udevice *dev, unsigned int speed_hz)
 	return 0;
 }
 
+/*
+ * I2C is a synchronous protocol and resets of the processor in the middle
+ * of an access can block the I2C Bus until a powerdown of the full unit is
+ * done. This function toggles the SCL until the SCL and SCA line are
+ * released, but max. 16 times, after this a I2C start-sequence is sent.
+ * This I2C Deblocking mechanism was developed by Keymile in association
+ * with Anatech and Atmel in 1998.
+ */
+static void i2c_gpio_make_abort(struct udevice *dev)
+{
+	struct i2c_gpio_bus *bus = dev_get_priv(dev);
+	struct gpio_desc *scl = &bus->gpios[PIN_SCL];
+	struct gpio_desc *sda = &bus->gpios[PIN_SDA];
+	int scl_state = 0;
+	int sda_state = 0;
+	int i = 0;
+	int ret = 0;
+
+#define DELAY_ABORT_SEQ	62	/* @200kHz 9 clocks = 44us, 62us is ok */
+
+	i2c_gpio_scl_set(scl, 1);
+
+	if (!i2c_gpio_sda_get(sda)) {
+		ret = -1;
+		for (i = 0; i < 16; i++) {
+			i2c_gpio_scl_set(scl, 0);
+			udelay(DELAY_ABORT_SEQ);
+			i2c_gpio_scl_set(scl, 1);
+			udelay(DELAY_ABORT_SEQ);
+			scl_state = i2c_gpio_scl_get(scl);
+			sda_state = i2c_gpio_sda_get(sda);
+			if (scl_state && sda_state) {
+				ret = 0;
+				break;
+			}
+		}
+	}
+
+	if (!ret) {
+		for (i = 0; i < 5; i++) {
+			i2c_gpio_send_start(scl, sda, 2 * bus->udelay);
+			i2c_gpio_scl_set(scl, 0);
+		}
+	}
+
+	/* respect stop setup time */
+	udelay(DELAY_ABORT_SEQ);
+	i2c_gpio_scl_set(scl, 1);
+	udelay(DELAY_ABORT_SEQ);
+	i2c_gpio_sda_set(sda, 1);
+	i2c_gpio_sda_get(sda);
+}
+
+static int i2c_gpio_drv_probe(struct udevice *dev)
+{
+	if (dev_read_bool(dev, "i2c-gpio,deblock"))
+		i2c_gpio_make_abort(dev);
+
+	return 0;
+}
+
 static int i2c_gpio_ofdata_to_platdata(struct udevice *dev)
 {
 	struct i2c_gpio_bus *bus = dev_get_priv(dev);
@@ -341,6 +407,7 @@ U_BOOT_DRIVER(i2c_gpio) = {
 	.name	= "i2c-gpio",
 	.id	= UCLASS_I2C,
 	.of_match = i2c_gpio_ids,
+	.probe	= i2c_gpio_drv_probe,
 	.ofdata_to_platdata = i2c_gpio_ofdata_to_platdata,
 	.priv_auto_alloc_size = sizeof(struct i2c_gpio_bus),
 	.ops	= &i2c_gpio_ops,
-- 
2.24.1