[RFC,v4,1/1] i2c debug counters as sysfs attributes

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 84f12bf90644..53688b1d855a 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -270,11 +270,22 @@  EXPORT_SYMBOL_GPL(i2c_generic_scl_recovery);
 
 int i2c_recover_bus(struct i2c_adapter *adap)
 {
+
+	if (adap->stats == NULL)
+		i2c_adapter_create_stats_directory(adap);
+
 	if (!adap->bus_recovery_info)
 		return -EBUSY;
 
 	dev_dbg(&adap->dev, "Trying i2c bus recovery\n");
-	return adap->bus_recovery_info->recover_bus(adap);
+	int ret = adap->bus_recovery_info->recover_bus(adap);
+
+	if (ret == 0)
+		++(adap->stats->recovery_successes);
+	else
+		++(adap->stats->recovery_failures);
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(i2c_recover_bus);
 
@@ -2223,6 +2234,23 @@  int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 		trace_i2c_result(adap, num, ret);
 	}
 
+	if (adap->stats == NULL) {
+		i2c_adapter_create_stats_directory(adap);
+	}
+
+	if (ret < 0) {
+		if (ret == -ENXIO)
+			++(adap->stats->nacks);
+		else if (ret == -ETIMEDOUT)
+			++(adap->stats->timeouts);
+		else
+			++(adap->stats->bus_errors);
+	}
+
+	if (ret == num) {
+		++(adap->stats->transfers);
+	}
+
 	return ret;
 }
 EXPORT_SYMBOL(__i2c_transfer);
@@ -2485,6 +2513,7 @@  static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver)
 	}
 
 	kfree(temp_client);
+	i2c_adapter_create_stats_directory(adapter);
 	return err;
 }
 
@@ -2617,6 +2646,7 @@  void i2c_put_dma_safe_msg_buf(u8 *buf, struct i2c_msg *msg, bool xferred)
 
 	kfree(buf);
 }
+
 EXPORT_SYMBOL_GPL(i2c_put_dma_safe_msg_buf);
 
 MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index 77f576e51652..253622706b63 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -767,6 +767,100 @@  static void __exit i2c_dev_exit(void)
 	unregister_chrdev_region(MKDEV(I2C_MAJOR, 0), I2C_MINORS);
 }
 
+static struct i2c_adapter *kobj_to_adapter(struct device *pdev)
+{
+	struct kobject *dev_kobj;
+	struct device *dev;
+
+	dev_kobj = ((struct kobject *)pdev)->parent;
+	dev = container_of(dev_kobj, struct device, kobj);
+	return to_i2c_adapter(dev);
+}
+
+ssize_t bus_errors_show(struct device *pdev,
+			struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%llu\n", kobj_to_adapter(pdev)->stats->bus_errors);
+}
+DEVICE_ATTR_RO(bus_errors);
+
+ssize_t transfers_show(struct device *pdev,
+			     struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%llu\n", kobj_to_adapter(pdev)->stats->transfers);
+}
+DEVICE_ATTR_RO(transfers);
+
+ssize_t nacks_show(struct device *pdev,
+		   struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%llu\n", kobj_to_adapter(pdev)->stats->nacks);
+}
+DEVICE_ATTR_RO(nacks);
+
+ssize_t recovery_successes_show(struct device *pdev,
+				struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%llu\n", kobj_to_adapter(pdev)->stats->recovery_successes);
+}
+DEVICE_ATTR_RO(recovery_successes);
+
+ssize_t recovery_failures_show(struct device *pdev,
+			       struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%llu\n", kobj_to_adapter(pdev)->stats->recovery_failures);
+}
+DEVICE_ATTR_RO(recovery_failures);
+
+ssize_t timeouts_show(struct device *pdev,
+		      struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%llu\n", kobj_to_adapter(pdev)->stats->timeouts);
+}
+DEVICE_ATTR_RO(timeouts);
+
+/**
+ * i2c_adapter_create_stats_directory - creates folder for I2C statistics.
+ * @adapter: the i2c_adapter to create the stats directory for.
+ *
+ * Return: 0 if successful, 1 if failed.
+ */
+int i2c_adapter_create_stats_directory(struct i2c_adapter *adapter)
+{
+	struct i2c_adapter_stats *stats;
+	int ret = 1;
+
+	stats = kzalloc(sizeof(*stats), GFP_KERNEL);
+	if (!stats) {
+		adapter->stats = NULL;
+		return ret;
+	}
+	adapter->stats = stats;
+	adapter->stats->kobj = kobject_create_and_add("stats", &adapter->dev.kobj);
+
+	ret = sysfs_create_file(adapter->stats->kobj, &dev_attr_transfers.attr);
+	if (ret)
+		dev_warn(&adapter->dev, "Failed to create sysfs file for tx_complete_cnt\n");
+
+	ret = sysfs_create_file(adapter->stats->kobj, &dev_attr_bus_errors.attr);
+	if (ret)
+		dev_warn(&adapter->dev, "Failed to create sysfs file for bus_errors\n");
+
+	ret = sysfs_create_file(adapter->stats->kobj, &dev_attr_nacks.attr);
+	if (ret)
+		dev_warn(&adapter->dev, "Failed to create sysfs file for nacks\n");
+
+	ret = sysfs_create_file(adapter->stats->kobj, &dev_attr_recovery_successes.attr);
+	if (ret)
+		dev_warn(&adapter->dev, "Failed to create sysfs file for recovery_successes\n");
+
+	ret = sysfs_create_file(adapter->stats->kobj, &dev_attr_recovery_failures.attr);
+	if (ret)
+		dev_warn(&adapter->dev, "Failed to create sysfs file for recovery_failures\n");
+
+	return ret;
+}
+
 MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>");
 MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
 MODULE_DESCRIPTION("I2C /dev entries driver");
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 3eb60a2e9e61..c8608378da2a 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -21,6 +21,7 @@ 
 #include <linux/of.h>		/* for struct device_node */
 #include <linux/swab.h>		/* for swab16 */
 #include <uapi/linux/i2c.h>
+#include <linux/slab.h> /* for kzalloc */
 
 extern struct bus_type i2c_bus_type;
 extern struct device_type i2c_adapter_type;
@@ -684,6 +685,25 @@  struct i2c_adapter_quirks {
 	u16 max_comb_2nd_msg_len;
 };
 
+/**
+ * I2C statistics
+ * The list of statistics are currently copied from npcm7xx.
+ * Perhaps a more universal set of statistics can be used.
+ *
+ * The stats are currently modeled as pointers to members in the bus drivers.
+ * A null pointer indicates the counter is not supported by the bus driver.
+ */
+struct i2c_adapter_stats {
+	struct kobject *kobj;
+
+	u64 transfers;
+	u64 bus_errors;
+	u64 nacks;
+	u64 recovery_successes;
+	u64 recovery_failures;
+	u64 timeouts;
+};
+
 /* enforce max_num_msgs = 2 and use max_comb_*_len for length checks */
 #define I2C_AQ_COMB			BIT(0)
 /* first combined message must be write */
@@ -735,12 +755,18 @@  struct i2c_adapter {
 
 	struct i2c_bus_recovery_info *bus_recovery_info;
 	const struct i2c_adapter_quirks *quirks;
+	struct i2c_adapter_stats *stats;
 
 	struct irq_domain *host_notify_domain;
 	struct regulator *bus_regulator;
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)
 
+int i2c_adapter_create_stats_directory(struct i2c_adapter *adapter);
+
+void i2c_adapter_stats_register_counter(struct i2c_adapter *adapter,
+					const char *counter_name, void *data_source);
+
 static inline void *i2c_get_adapdata(const struct i2c_adapter *adap)
 {
 	return dev_get_drvdata(&adap->dev);