i2c: Replace list-based mechanism for handling auto-detected clients

So far a list is used to track auto-detected clients per driver.
The same functionality can be achieved much simpler by flagging
auto-detected clients.

Two notes regarding the usage of driver_for_each_device:
In our case it can't fail, however the function is annotated __must_check.
So a little workaround is needed to avoid a compiler warning.
Then we may remove nodes from the list over which we iterate.
This is safe, see the explanation at the beginning of lib/klist.c.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
[wsa: fixed description of the new flag]
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Author: hkallweit

drivers/i2c/i2c-core-base.c

@@ -1696,23 +1696,6 @@ int i2c_add_numbered_adapter(struct i2c_adapter *adap)
 }
 EXPORT_SYMBOL_GPL(i2c_add_numbered_adapter);
 
-static void i2c_do_del_adapter(struct i2c_driver *driver,
-			      struct i2c_adapter *adapter)
-{
-	struct i2c_client *client, *_n;
-
-	/* Remove the devices we created ourselves as the result of hardware
-	 * probing (using a driver's detect method) */
-	list_for_each_entry_safe(client, _n, &driver->clients, detected) {
-		if (client->adapter == adapter) {
-			dev_dbg(&adapter->dev, "Removing %s at 0x%x\n",
-				client->name, client->addr);
-			list_del(&client->detected);
-			i2c_unregister_device(client);
-		}
-	}
-}
-
 static int __unregister_client(struct device *dev, void *dummy)
 {
 	struct i2c_client *client = i2c_verify_client(dev);
@@ -1728,12 +1711,6 @@ static int __unregister_dummy(struct device *dev, void *dummy)
 	return 0;
 }
 
-static int __process_removed_adapter(struct device_driver *d, void *data)
-{
-	i2c_do_del_adapter(to_i2c_driver(d), data);
-	return 0;
-}
-
 /**
  * i2c_del_adapter - unregister I2C adapter
  * @adap: the adapter being unregistered
@@ -1757,11 +1734,6 @@ void i2c_del_adapter(struct i2c_adapter *adap)
 	}
 
 	i2c_acpi_remove_space_handler(adap);
-	/* Tell drivers about this removal */
-	mutex_lock(&core_lock);
-	bus_for_each_drv(&i2c_bus_type, NULL, adap,
-			       __process_removed_adapter);
-	mutex_unlock(&core_lock);
 
 	/* Remove devices instantiated from sysfs */
 	mutex_lock_nested(&adap->userspace_clients_lock,
@@ -1780,8 +1752,10 @@ void i2c_del_adapter(struct i2c_adapter *adap)
 	 * we can't remove the dummy devices during the first pass: they
 	 * could have been instantiated by real devices wishing to clean
 	 * them up properly, so we give them a chance to do that first. */
+	mutex_lock(&core_lock);
 	device_for_each_child(&adap->dev, NULL, __unregister_client);
 	device_for_each_child(&adap->dev, NULL, __unregister_dummy);
+	mutex_unlock(&core_lock);
 
 	/* device name is gone after device_unregister */
 	dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
@@ -2001,7 +1975,6 @@ int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
 	/* add the driver to the list of i2c drivers in the driver core */
 	driver->driver.owner = owner;
 	driver->driver.bus = &i2c_bus_type;
-	INIT_LIST_HEAD(&driver->clients);
 
 	/* When registration returns, the driver core
 	 * will have called probe() for all matching-but-unbound devices.
@@ -2019,10 +1992,13 @@ int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
 }
 EXPORT_SYMBOL(i2c_register_driver);
 
-static int __process_removed_driver(struct device *dev, void *data)
+static int __i2c_unregister_detected_client(struct device *dev, void *argp)
 {
-	if (dev->type == &i2c_adapter_type)
-		i2c_do_del_adapter(data, to_i2c_adapter(dev));
+	struct i2c_client *client = i2c_verify_client(dev);
+
+	if (client && client->flags & I2C_CLIENT_AUTO)
+		i2c_unregister_device(client);
+
 	return 0;
 }
 
@@ -2033,7 +2009,12 @@ static int __process_removed_driver(struct device *dev, void *data)
  */
 void i2c_del_driver(struct i2c_driver *driver)
 {
-	i2c_for_each_dev(driver, __process_removed_driver);
+	mutex_lock(&core_lock);
+	/* Satisfy __must_check, function can't fail */
+	if (driver_for_each_device(&driver->driver, NULL, NULL,
+				   __i2c_unregister_detected_client)) {
+	}
+	mutex_unlock(&core_lock);
 
 	driver_unregister(&driver->driver);
 	pr_debug("driver [%s] unregistered\n", driver->driver.name);
@@ -2460,6 +2441,7 @@ static int i2c_detect_address(struct i2c_client *temp_client,
 	/* Finally call the custom detection function */
 	memset(&info, 0, sizeof(struct i2c_board_info));
 	info.addr = addr;
+	info.flags = I2C_CLIENT_AUTO;
 	err = driver->detect(temp_client, &info);
 	if (err) {
 		/* -ENODEV is returned if the detection fails. We catch it
@@ -2486,9 +2468,7 @@ static int i2c_detect_address(struct i2c_client *temp_client,
 		dev_dbg(&adapter->dev, "Creating %s at 0x%02x\n",
 			info.type, info.addr);
 		client = i2c_new_client_device(adapter, &info);
-		if (!IS_ERR(client))
-			list_add_tail(&client->detected, &driver->clients);
-		else
+		if (IS_ERR(client))
 			dev_err(&adapter->dev, "Failed creating %s at 0x%02x\n",
 				info.type, info.addr);
 	}

include/linux/i2c.h

@@ -244,7 +244,6 @@ enum i2c_driver_flags {
  * @id_table: List of I2C devices supported by this driver
  * @detect: Callback for device detection
  * @address_list: The I2C addresses to probe (for detect)
- * @clients: List of detected clients we created (for i2c-core use only)
  * @flags: A bitmask of flags defined in &enum i2c_driver_flags
  *
  * The driver.owner field should be set to the module owner of this driver.
@@ -299,7 +298,6 @@ struct i2c_driver {
 	/* Device detection callback for automatic device creation */
 	int (*detect)(struct i2c_client *client, struct i2c_board_info *info);
 	const unsigned short *address_list;
-	struct list_head clients;
 
 	u32 flags;
 };
@@ -334,6 +332,7 @@ struct i2c_client {
 #define I2C_CLIENT_SLAVE	0x20	/* we are the slave */
 #define I2C_CLIENT_HOST_NOTIFY	0x40	/* We want to use I2C host notify */
 #define I2C_CLIENT_WAKE		0x80	/* for board_info; true iff can wake */
+#define I2C_CLIENT_AUTO		0x100	/* client was auto-detected */
 #define I2C_CLIENT_SCCB		0x9000	/* Use Omnivision SCCB protocol */
 					/* Must match I2C_M_STOP|IGNORE_NAK */