i2c: Add bus recovery infrastructure

Add i2c bus recovery infrastructure to i2c adapters as specified in the i2c
protocol Rev. 03 section 3.1.16 titled "Bus clear".

http://www.nxp.com/documents/user_manual/UM10204.pdf

Sometimes during operation i2c bus hangs and we need to give dummy clocks to
slave device to start the transfer again. Now we may have capability in the bus
controller to generate these clocks or platform may have gpio pins which can be
toggled to generate dummy clocks. This patch supports both.

This patch also adds in generic bus recovery routines gpio or scl line based
which can be used by bus controller. In addition controller driver may provide
its own version of the bus recovery routine.

This doesn't support multi-master recovery for now.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
[wsa: changed gpio type to int and minor reformatting]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/i2c-core.c

@@ -27,7 +27,9 @@
 
 #include <linux/module.h>
 #include <linux/kernel.h>
+#include <linux/delay.h>
 #include <linux/errno.h>
+#include <linux/gpio.h>
 #include <linux/slab.h>
 #include <linux/i2c.h>
 #include <linux/init.h>
@@ -109,6 +111,130 @@ static int i2c_device_uevent(struct device *dev, struct kobj_uevent_env *env)
 #define i2c_device_uevent	NULL
 #endif	/* CONFIG_HOTPLUG */
 
+/* i2c bus recovery routines */
+static int get_scl_gpio_value(struct i2c_adapter *adap)
+{
+	return gpio_get_value(adap->bus_recovery_info->scl_gpio);
+}
+
+static void set_scl_gpio_value(struct i2c_adapter *adap, int val)
+{
+	gpio_set_value(adap->bus_recovery_info->scl_gpio, val);
+}
+
+static int get_sda_gpio_value(struct i2c_adapter *adap)
+{
+	return gpio_get_value(adap->bus_recovery_info->sda_gpio);
+}
+
+static int i2c_get_gpios_for_recovery(struct i2c_adapter *adap)
+{
+	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
+	struct device *dev = &adap->dev;
+	int ret = 0;
+
+	ret = gpio_request_one(bri->scl_gpio, GPIOF_OPEN_DRAIN |
+			GPIOF_OUT_INIT_HIGH, "i2c-scl");
+	if (ret) {
+		dev_warn(dev, "Can't get SCL gpio: %d\n", bri->scl_gpio);
+		return ret;
+	}
+
+	if (bri->get_sda) {
+		if (gpio_request_one(bri->sda_gpio, GPIOF_IN, "i2c-sda")) {
+			/* work without SDA polling */
+			dev_warn(dev, "Can't get SDA gpio: %d. Not using SDA polling\n",
+					bri->sda_gpio);
+			bri->get_sda = NULL;
+		}
+	}
+
+	return ret;
+}
+
+static void i2c_put_gpios_for_recovery(struct i2c_adapter *adap)
+{
+	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
+
+	if (bri->get_sda)
+		gpio_free(bri->sda_gpio);
+
+	gpio_free(bri->scl_gpio);
+}
+
+/*
+ * We are generating clock pulses. ndelay() determines durating of clk pulses.
+ * We will generate clock with rate 100 KHz and so duration of both clock levels
+ * is: delay in ns = (10^6 / 100) / 2
+ */
+#define RECOVERY_NDELAY		5000
+#define RECOVERY_CLK_CNT	9
+
+static int i2c_generic_recovery(struct i2c_adapter *adap)
+{
+	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
+	int i = 0, val = 1, ret = 0;
+
+	if (bri->prepare_recovery)
+		bri->prepare_recovery(bri);
+
+	/*
+	 * By this time SCL is high, as we need to give 9 falling-rising edges
+	 */
+	while (i++ < RECOVERY_CLK_CNT * 2) {
+		if (val) {
+			/* Break if SDA is high */
+			if (bri->get_sda && bri->get_sda(adap))
+					break;
+			/* SCL shouldn't be low here */
+			if (!bri->get_scl(adap)) {
+				dev_err(&adap->dev,
+					"SCL is stuck low, exit recovery\n");
+				ret = -EBUSY;
+				break;
+			}
+		}
+
+		val = !val;
+		bri->set_scl(adap, val);
+		ndelay(RECOVERY_NDELAY);
+	}
+
+	if (bri->unprepare_recovery)
+		bri->unprepare_recovery(bri);
+
+	return ret;
+}
+
+int i2c_generic_scl_recovery(struct i2c_adapter *adap)
+{
+	adap->bus_recovery_info->set_scl(adap, 1);
+	return i2c_generic_recovery(adap);
+}
+
+int i2c_generic_gpio_recovery(struct i2c_adapter *adap)
+{
+	int ret;
+
+	ret = i2c_get_gpios_for_recovery(adap);
+	if (ret)
+		return ret;
+
+	ret = i2c_generic_recovery(adap);
+	i2c_put_gpios_for_recovery(adap);
+
+	return ret;
+}
+
+int i2c_recover_bus(struct i2c_adapter *adap)
+{
+	if (!adap->bus_recovery_info)
+		return -EOPNOTSUPP;
+
+	dev_dbg(&adap->dev, "Trying i2c bus recovery\n");
+	return adap->bus_recovery_info->recover_bus(adap);
+}
+
 static int i2c_device_probe(struct device *dev)
 {
 	struct i2c_client	*client = i2c_verify_client(dev);
@@ -902,6 +1028,39 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
 			 "Failed to create compatibility class link\n");
 #endif
 
+	/* bus recovery specific initialization */
+	if (adap->bus_recovery_info) {
+		struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
+
+		if (!bri->recover_bus) {
+			dev_err(&adap->dev, "No recover_bus() found, not using recovery\n");
+			adap->bus_recovery_info = NULL;
+			goto exit_recovery;
+		}
+
+		/* Generic GPIO recovery */
+		if (bri->recover_bus == i2c_generic_gpio_recovery) {
+			if (!gpio_is_valid(bri->scl_gpio)) {
+				dev_err(&adap->dev, "Invalid SCL gpio, not using recovery\n");
+				adap->bus_recovery_info = NULL;
+				goto exit_recovery;
+			}
+
+			if (gpio_is_valid(bri->sda_gpio))
+				bri->get_sda = get_sda_gpio_value;
+			else
+				bri->get_sda = NULL;
+
+			bri->get_scl = get_scl_gpio_value;
+			bri->set_scl = set_scl_gpio_value;
+		} else if (!bri->set_scl || !bri->get_scl) {
+			/* Generic SCL recovery */
+			dev_err(&adap->dev, "No {get|set}_gpio() found, not using recovery\n");
+			adap->bus_recovery_info = NULL;
+		}
+	}
+
+exit_recovery:
 	/* create pre-declared device nodes */
 	if (adap->nr < __i2c_first_dynamic_bus_num)
 		i2c_scan_static_board_info(adap);

include/linux/i2c.h

@@ -370,6 +370,45 @@ struct i2c_algorithm {
 	u32 (*functionality) (struct i2c_adapter *);
 };
 
+/**
+ * struct i2c_bus_recovery_info - I2C bus recovery information
+ * @recover_bus: Recover routine. Either pass driver's recover_bus() routine, or
+ *	i2c_generic_scl_recovery() or i2c_generic_gpio_recovery().
+ * @get_scl: This gets current value of SCL line. Mandatory for generic SCL
+ *      recovery. Used internally for generic GPIO recovery.
+ * @set_scl: This sets/clears SCL line. Mandatory for generic SCL recovery. Used
+ *      internally for generic GPIO recovery.
+ * @get_sda: This gets current value of SDA line. Optional for generic SCL
+ *      recovery. Used internally, if sda_gpio is a valid GPIO, for generic GPIO
+ *      recovery.
+ * @prepare_recovery: This will be called before starting recovery. Platform may
+ *	configure padmux here for SDA/SCL line or something else they want.
+ * @unprepare_recovery: This will be called after completing recovery. Platform
+ *	may configure padmux here for SDA/SCL line or something else they want.
+ * @scl_gpio: gpio number of the SCL line. Only required for GPIO recovery.
+ * @sda_gpio: gpio number of the SDA line. Only required for GPIO recovery.
+ */
+struct i2c_bus_recovery_info {
+	int (*recover_bus)(struct i2c_adapter *);
+
+	int (*get_scl)(struct i2c_adapter *);
+	void (*set_scl)(struct i2c_adapter *, int val);
+	int (*get_sda)(struct i2c_adapter *);
+
+	void (*prepare_recovery)(struct i2c_bus_recovery_info *bri);
+	void (*unprepare_recovery)(struct i2c_bus_recovery_info *bri);
+
+	/* gpio recovery */
+	int scl_gpio;
+	int sda_gpio;
+};
+
+int i2c_recover_bus(struct i2c_adapter *adap);
+
+/* Generic recovery routines */
+int i2c_generic_gpio_recovery(struct i2c_adapter *adap);
+int i2c_generic_scl_recovery(struct i2c_adapter *adap);
+
 /*
  * i2c_adapter is the structure used to identify a physical i2c bus along
  * with the access algorithms necessary to access it.
@@ -393,6 +432,8 @@ struct i2c_adapter {
 
 	struct mutex userspace_clients_lock;
 	struct list_head userspace_clients;
+
+	struct i2c_bus_recovery_info *bus_recovery_info;
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)