[PATCH V3 1/2] i2c/adapter: Add bus recovery infrastructure

[Viresh Kumar <viresh.kumar-qxv4g6HH51o@public.gmane.org>]

Add i2c bus recovery infrastructure to i2c adapters as specified in the i2c
protocol Rev. 03 section 3.16 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.

Signed-off-by: Viresh Kumar <viresh.kumar-qxv4g6HH51o@public.gmane.org>
---
 drivers/i2c/i2c-core.c |  125 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/i2c.h    |   52 ++++++++++++++++++++
 2 files changed, 177 insertions(+), 0 deletions(-)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index e9c1893..5cd5f83 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -26,7 +26,9 @@
 
 #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>
@@ -103,6 +105,88 @@ 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 i2c_gpio_recover_bus(struct i2c_adapter *adap)
+{
+	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
+	unsigned long delay = 1000000;
+	int i, ret, val = 1;
+
+	if (bri->get_gpio)
+		bri->get_gpio(bri->scl_gpio);
+
+	ret = gpio_request_one(bri->scl_gpio, bri->scl_gpio_flags, "i2c-scl");
+	if (ret < 0) {
+		dev_warn(&adap->dev, "gpio request fail: %d\n", bri->scl_gpio);
+		return ret;
+	}
+
+	if (!bri->skip_sda_polling) {
+		if (bri->get_gpio)
+			bri->get_gpio(bri->sda_gpio);
+
+		ret = gpio_request_one(bri->sda_gpio, bri->sda_gpio_flags,
+				"i2c-sda");
+		if (ret < 0) {
+			/* work without sda polling */
+			dev_warn(&adap->dev,
+				"sda_gpio request fail: %d. Skip sda polling\n",
+				bri->scl_gpio);
+			bri->skip_sda_polling = true;
+			if (bri->put_gpio)
+				bri->put_gpio(bri->sda_gpio);
+		}
+	}
+
+	delay /= bri->clock_rate_khz * 2;
+
+	for (i = 0; i < bri->clock_cnt * 2; i++, val = !val) {
+		ndelay(delay);
+		gpio_set_value(bri->scl_gpio, val);
+
+		/* break if sda got high, check only when scl line is high */
+		if (!bri->skip_sda_polling && val)
+			if (gpio_get_value(bri->sda_gpio))
+				break;
+	}
+
+	gpio_free(bri->scl_gpio);
+
+	if (bri->put_gpio)
+		bri->put_gpio(bri->scl_gpio);
+
+	if (!bri->skip_sda_polling) {
+		gpio_free(bri->sda_gpio);
+
+		if (bri->put_gpio)
+			bri->put_gpio(bri->sda_gpio);
+	}
+
+	return 0;
+}
+
+static int i2c_scl_recover_bus(struct i2c_adapter *adap)
+{
+	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
+	int i, val = 0;
+	unsigned long delay = 1000000;
+
+	delay /= bri->clock_rate_khz * 2;
+
+	for (i = 0; i < bri->clock_cnt * 2; i++,
+			val = !val) {
+		bri->set_scl(adap, val);
+		ndelay(delay);
+
+		/* break if sda got high, check only when scl line is high */
+		if (!bri->skip_sda_polling && val)
+			if (bri->get_sda(adap))
+				break;
+	}
+
+	return 0;
+}
+
 static int i2c_device_probe(struct device *dev)
 {
 	struct i2c_client	*client = i2c_verify_client(dev);
@@ -861,6 +945,47 @@ 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_info(&adap->dev,
+				"registered for non-generic bus recovery\n");
+		} else {
+			/* Use generic recovery routines */
+			if (!bri->clock_rate_khz) {
+				dev_warn(&adap->dev,
+					"doesn't have valid recovery clock rate\n");
+				goto exit_recovery;
+			}
+
+			/* Most controller need 9 clocks at max */
+			if (!bri->clock_cnt)
+				bri->clock_cnt = 9;
+
+			if (bri->is_gpio_recovery) {
+				bri->recover_bus = i2c_gpio_recover_bus;
+				dev_info(&adap->dev,
+					"registered for gpio bus recovery\n");
+			} else if (bri->set_scl) {
+				if (!bri->skip_sda_polling && !bri->get_sda) {
+					dev_warn(&adap->dev,
+						"!get_sda. skip sda polling\n");
+					bri->skip_sda_polling = true;
+				}
+
+				bri->recover_bus = i2c_scl_recover_bus;
+				dev_info(&adap->dev,
+					"registered for scl bus recovery\n");
+			} else {
+				dev_warn(&adap->dev,
+					"doesn't have valid recovery type\n");
+			}
+		}
+	}
+
+exit_recovery:
 	/* create pre-declared device nodes */
 	if (adap->nr < __i2c_first_dynamic_bus_num)
 		i2c_scan_static_board_info(adap);
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 8e25a91..1310d1a 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -365,6 +365,55 @@ 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
+ *	pass it NULL to use generic ones, i.e. gpio or scl based.
+ * @skip_sda_polling: if true, bus recovery will not poll sda line to check if
+ *	it became high or not. Only required if recover_bus == NULL.
+ * @is_gpio_recovery: true, select gpio type else scl type. Only required if
+ *	recover_bus == NULL.
+ * @clock_rate_khz: clock rate of dummy clock in khz. Required for both gpio and
+ *	scl type recovery.
+ * @clock_cnt: count of max clocks to be generated. Required for both gpio and
+ *	scl type recovery.
+ * @set_scl: controller specific scl configuration routine. Only required if
+ *	is_gpio_recovery == false
+ * @get_sda: controller specific sda read routine. Only required if
+ *	is_gpio_recovery == false and skip_sda_polling == false.
+ * @get_gpio: called before recover_bus() to get padmux configured for scl line.
+ *	as gpio. Only required if is_gpio_recovery == true.
+ * @put_gpio: called after recover_bus() to get padmux configured for scl line
+ *	as scl. Only required if is_gpio_recovery == true.
+ * @scl_gpio: gpio number of the scl line. Only required if is_gpio_recovery ==
+ *	true.
+ * @sda_gpio: gpio number of the sda line. Only required if is_gpio_recovery ==
+ *	true and skip_sda_polling == false.
+ * @scl_gpio_flags: flag for gpio_request_one of scl_gpio. 0 implies
+ *	GPIOF_OUT_INIT_LOW.
+ * @sda_gpio_flags: flag for gpio_request_one of sda_gpio. 0 implies
+ *	GPIOF_OUT_INIT_LOW.
+ */
+struct i2c_bus_recovery_info {
+	int (*recover_bus)(struct i2c_adapter *);
+	bool skip_sda_polling;
+	bool is_gpio_recovery;
+	u32 clock_rate_khz;
+	u8 clock_cnt;
+
+	/* scl/sda recovery */
+	void (*set_scl)(struct i2c_adapter *, int val);
+	int (*get_sda)(struct i2c_adapter *);
+
+	/* gpio recovery */
+	int (*get_gpio)(unsigned gpio);
+	int (*put_gpio)(unsigned gpio);
+	u32 scl_gpio;
+	u32 sda_gpio;
+	u32 scl_gpio_flags;
+	u32 sda_gpio_flags;
+};
+
 /*
  * i2c_adapter is the structure used to identify a physical i2c bus along
  * with the access algorithms necessary to access it.
@@ -388,6 +437,9 @@ struct i2c_adapter {
 
 	struct mutex userspace_clients_lock;
 	struct list_head userspace_clients;
+
+	/* Pass valid pointer if recovery infrastructure is required */
+	struct i2c_bus_recovery_info *bus_recovery_info;
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)
 
-- 
1.7.8.110.g4cb5d