i2c-core: Erase pointer to clientdata on removal

After discovering that a lot of i2c-drivers leave the pointer to their
clientdata dangling, it was decided to let the core handle this issue.
It is assumed that the core may access the private data after remove()
as there are no guarantees for the lifetime of such pointers anyhow (see
thread starting at http://lkml.org/lkml/2010/3/21/68)
Signed-off-by: NWolfram Sang <w.sang@pengutronix.de>
Signed-off-by: NJean Delvare <khali@linux-fr.org>

Documentation/i2c/writing-clients

@@ -74,6 +74,11 @@ structure at all.  You should use this to keep device-specific data.
 	/* retrieve the value */
 	void *i2c_get_clientdata(const struct i2c_client *client);
 
+Note that starting with kernel 2.6.34, you don't have to set the `data' field
+to NULL in remove() or if probe() failed anymore. The i2c-core does this
+automatically on these occasions. Those are also the only times the core will
+touch this field.
+
 
 Accessing the client
 ====================

drivers/i2c/i2c-core.c

@@ -117,8 +117,10 @@ static int i2c_device_probe(struct device *dev)
 	dev_dbg(dev, "probe\n");
 
 	status = driver->probe(client, i2c_match_id(driver->id_table, client));
-	if (status)
+	if (status) {
 		client->driver = NULL;
+		i2c_set_clientdata(client, NULL);
+	}
 	return status;
 }
 
@@ -139,8 +141,10 @@ static int i2c_device_remove(struct device *dev)
 		dev->driver = NULL;
 		status = 0;
 	}
-	if (status == 0)
+	if (status == 0) {
 		client->driver = NULL;
+		i2c_set_clientdata(client, NULL);
+	}
 	return status;
 }