[PATCH 2/4] i2c: core: add generic I2C GPIO recovery

[Codrin Ciubotariu <codrin.ciubotariu@microchip.com>]

Multiple I2C bus drivers use similar bindings to obtain information needed
for I2C recovery. For example, for platforms using device-tree, the
properties look something like this:

&i2c {
	...
	pinctrl-names = "default", "gpio";
	pinctrl-0 = <&pinctrl_i2c_default>;
	pinctrl-1 = <&pinctrl_i2c_gpio>;
	sda-gpios = <&pio 0 GPIO_ACTIVE_HIGH>;
	scl-gpios = <&pio 1 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
	...
}

For this reason, we can add this common initialization in the core. This
way, other I2C bus drivers will be able to support GPIO recovery just by
providing a pointer to platform's pinctrl and calling i2c_recover_bus()
when SDA is stuck low.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
---

Changes from RFC:
 - removed comment with "recovery" pinctrl state from description;
 - pinctrl state is changed to gpio after calling prepare_recovery()
   callback;
 - addressed requested changes on comments;
 - removed cleanup_pinctrl label from i2c_gpio_init_pinctrl_recovery()
 - added glitch protection for SDA line when its corresponding gpio is
   taken at initialization;

 drivers/i2c/i2c-core-base.c | 126 ++++++++++++++++++++++++++++++++++++
 include/linux/i2c.h         |  11 ++++
 2 files changed, 137 insertions(+)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 69217d2193da..cf0c5eb152e1 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -32,6 +32,7 @@
 #include <linux/of_device.h>
 #include <linux/of.h>
 #include <linux/of_irq.h>
+#include <linux/pinctrl/consumer.h>
 #include <linux/pm_domain.h>
 #include <linux/pm_runtime.h>
 #include <linux/pm_wakeirq.h>
@@ -181,6 +182,8 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
 
 	if (bri->prepare_recovery)
 		bri->prepare_recovery(adap);
+	if (bri->pinctrl)
+		pinctrl_select_state(bri->pinctrl, bri->pins_gpio);
 
 	/*
 	 * If we can set SDA, we will always create a STOP to ensure additional
@@ -236,6 +239,8 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
 
 	if (bri->unprepare_recovery)
 		bri->unprepare_recovery(adap);
+	if (bri->pinctrl)
+		pinctrl_select_state(bri->pinctrl, bri->pins_default);
 
 	return ret;
 }
@@ -251,6 +256,125 @@ int i2c_recover_bus(struct i2c_adapter *adap)
 }
 EXPORT_SYMBOL_GPL(i2c_recover_bus);
 
+static void i2c_gpio_init_pinctrl_recovery(struct i2c_adapter *adap)
+{
+	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
+	struct device *dev = &adap->dev;
+	struct pinctrl *p = bri->pinctrl;
+
+	/*
+	 * we can't change states without pinctrl, so remove the states if
+	 * populated
+	 */
+	if (!p) {
+		bri->pins_default = NULL;
+		bri->pins_gpio = NULL;
+		return;
+	}
+
+	if (!bri->pins_default) {
+		bri->pins_default = pinctrl_lookup_state(p,
+							 PINCTRL_STATE_DEFAULT);
+		if (IS_ERR(bri->pins_default)) {
+			dev_dbg(dev, PINCTRL_STATE_DEFAULT " state not found for GPIO recovery\n");
+			bri->pins_default = NULL;
+		}
+	}
+	if (!bri->pins_gpio) {
+		bri->pins_gpio = pinctrl_lookup_state(p, "gpio");
+		if (IS_ERR(bri->pins_gpio))
+			bri->pins_gpio = pinctrl_lookup_state(p, "recovery");
+
+		if (IS_ERR(bri->pins_gpio)) {
+			dev_dbg(dev, "no gpio or recovery state found for GPIO recovery\n");
+			bri->pins_gpio = NULL;
+		}
+	}
+
+	/* for pinctrl state changes, we need all the information */
+	if (!bri->pins_default || !bri->pins_gpio) {
+		bri->pinctrl = NULL;
+		bri->pins_default = NULL;
+		bri->pins_gpio = NULL;
+	} else {
+		dev_info(dev, "using pinctrl states for GPIO recovery");
+	}
+}
+
+static int i2c_gpio_init_generic_recovery(struct i2c_adapter *adap)
+{
+	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
+	struct device *dev = &adap->dev;
+	struct gpio_desc *gpiod;
+	int ret = 0;
+
+	/*
+	 * don't touch the recovery information if the driver is not using
+	 * generic SCL recovery
+	 */
+	if (bri->recover_bus && bri->recover_bus != i2c_generic_scl_recovery)
+		return 0;
+
+	/*
+	 * pins might be taken as GPIO, so we should inform pinctrl about
+	 * this and move the state to GPIO
+	 */
+	if (bri->pinctrl)
+		pinctrl_select_state(bri->pinctrl, bri->pins_gpio);
+
+	/*
+	 * if there is incomplete or no recovery information, see if generic
+	 * GPIO recovery is available
+	 */
+	if (!bri->scl_gpiod) {
+		gpiod = devm_gpiod_get(dev, "scl", GPIOD_OUT_HIGH_OPEN_DRAIN);
+		if (PTR_ERR(gpiod) == -EPROBE_DEFER) {
+			ret  = -EPROBE_DEFER;
+			goto cleanup_pinctrl_state;
+		}
+		if (!IS_ERR(gpiod)) {
+			bri->scl_gpiod = gpiod;
+			bri->recover_bus = i2c_generic_scl_recovery;
+			dev_info(dev, "using generic GPIOs for recovery\n");
+		}
+	}
+
+	/* SDA GPIOD line is optional, so we care about DEFER only */
+	if (!bri->sda_gpiod) {
+		/*
+		 * We have SCL. Pull SCL low and wait a bit so that SDA glitches
+		 * have no effect.
+		 */
+		gpiod_direction_output(bri->scl_gpiod, 0);
+		udelay(10);
+		gpiod = devm_gpiod_get(dev, "sda", GPIOD_IN);
+
+		/* Wait a bit in case of a SDA glitch, and then release SCL. */
+		udelay(10);
+		gpiod_direction_output(bri->scl_gpiod, 1);
+
+		if (PTR_ERR(gpiod) == -EPROBE_DEFER) {
+			ret = -EPROBE_DEFER;
+			goto cleanup_pinctrl_state;
+		}
+		if (!IS_ERR(gpiod))
+			bri->sda_gpiod = gpiod;
+	}
+
+cleanup_pinctrl_state:
+	/* change the state of the pins back to their default state */
+	if (bri->pinctrl)
+		pinctrl_select_state(bri->pinctrl, bri->pins_default);
+
+	return ret;
+}
+
+static int i2c_gpio_init_recovery(struct i2c_adapter *adap)
+{
+	i2c_gpio_init_pinctrl_recovery(adap);
+	return i2c_gpio_init_generic_recovery(adap);
+}
+
 static void i2c_init_recovery(struct i2c_adapter *adap)
 {
 	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
@@ -259,6 +383,8 @@ static void i2c_init_recovery(struct i2c_adapter *adap)
 	if (!bri)
 		return;
 
+	i2c_gpio_init_recovery(adap);
+
 	if (!bri->recover_bus) {
 		err_str = "no recover_bus() found";
 		goto err;
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 176bf971cbe0..93b6b698f150 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -606,6 +606,14 @@ struct i2c_timings {
  *	may configure padmux here for SDA/SCL line or something else they want.
  * @scl_gpiod: gpiod of the SCL line. Only required for GPIO recovery.
  * @sda_gpiod: gpiod of the SDA line. Only required for GPIO recovery.
+ * @pinctrl: pinctrl used by GPIO recovery to change the state of the I2C pins.
+ *      Optional.
+ * @pins_default: default state of SCL/SDA lines, when they are assigned to the
+ *      I2C bus. Optional. Populated internally for GPIO recovery, if a state with
+ *      the name PINCTRL_STATE_DEFAULT is found and pinctrl is valid.
+ * @pins_gpio: recovery state of SCL/SDA lines, when they are used as GPIOs.
+ *      Optional. Populated internally for GPIO recovery, if this state is called
+ *      "gpio" or "recovery" and pinctrl is valid.
  */
 struct i2c_bus_recovery_info {
 	int (*recover_bus)(struct i2c_adapter *adap);
@@ -622,6 +630,9 @@ struct i2c_bus_recovery_info {
 	/* gpio recovery */
 	struct gpio_desc *scl_gpiod;
 	struct gpio_desc *sda_gpiod;
+	struct pinctrl *pinctrl;
+	struct pinctrl_state *pins_default;
+	struct pinctrl_state *pins_gpio;
 };
 
 int i2c_recover_bus(struct i2c_adapter *adap);
-- 
2.25.1