i2c: add core-managed per-client directory in debugfs

More and more I2C client drivers use debugfs entries and currently they
need to manage a subdir for their files on their own. This means
inconsistent naming for these subdirs and they are scattered all over
the debugfs-tree as well. Not to mention the duplicated code.

Let the I2C core provide and maintain a proper directory per client.

Note: It was considered to save the additional pointer in 'struct
i2c_client' and only provide a subdir when requested via a helper
function. When sketching this approach, more and more corner cases
appeared, though, so the current solution with its simple and unabiguous
code was chosen.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>

drivers/i2c/i2c-core-base.c

@@ -1015,6 +1015,8 @@ i2c_new_client_device(struct i2c_adapter *adap, struct i2c_board_info const *inf
 	if (status)
 		goto out_remove_swnode;
 
+	client->debugfs = debugfs_create_dir(dev_name(&client->dev), adap->debugfs);
+
 	dev_dbg(&adap->dev, "client [%s] registered with bus id %s\n",
 		client->name, dev_name(&client->dev));
 
@@ -1058,6 +1060,8 @@ void i2c_unregister_device(struct i2c_client *client)
 
 	if (ACPI_COMPANION(&client->dev))
 		acpi_device_clear_enumerated(ACPI_COMPANION(&client->dev));
+
+	debugfs_remove_recursive(client->debugfs);
 	device_remove_software_node(&client->dev);
 	device_unregister(&client->dev);
 }

include/linux/i2c.h

@@ -347,6 +347,7 @@ struct i2c_client {
 	i2c_slave_cb_t slave_cb;	/* callback for slave mode	*/
 #endif
 	void *devres_group_id;		/* ID of probe devres group	*/
+	struct dentry *debugfs;		/* per-client debugfs dir	*/
 };
 #define to_i2c_client(d) container_of(d, struct i2c_client, dev)