i2c: mux: create "channel-n" symlinks for child segments in the mux device

This makes the topology clearer. For instance, by adding a pca9547
device with address 0x70 to bus i2c-0, you get:

/sys/class/i2c-dev/i2c-0/device/0-0070/channel-0 -> i2c-1
...
/sys/class/i2c-dev/i2c-0/device/0-0070/channel-7 -> i2c-8

Signed-off-by: Gerlando Falauto <gerlando.falauto@keymile.com>
[wsa: simplified sysfs-usage and fixed format string usage]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Martin Belanger <martin.belanger@cyaninc.com>
Acked-by: Danielle Costantino <danielle.costantino@gmail.com>

drivers/i2c/i2c-mux.c

@@ -110,6 +110,7 @@ struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
 						 void *, u32))
 {
 	struct i2c_mux_priv *priv;
+	char symlink_name[20];
 	int ret;
 
 	priv = kzalloc(sizeof(struct i2c_mux_priv), GFP_KERNEL);
@@ -186,6 +187,9 @@ struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
 	WARN(sysfs_create_link(&priv->adap.dev.kobj, &mux_dev->kobj, "mux_device"),
 			       "can't create symlink to mux device\n");
 
+	snprintf(symlink_name, sizeof(symlink_name), "channel-%u", chan_id);
+	WARN(sysfs_create_link(&mux_dev->kobj, &priv->adap.dev.kobj, symlink_name),
+			       "can't create symlink for channel %u\n", chan_id);
 	dev_info(&parent->dev, "Added multiplexed i2c bus %d\n",
 		 i2c_adapter_id(&priv->adap));
 
@@ -196,6 +200,10 @@ EXPORT_SYMBOL_GPL(i2c_add_mux_adapter);
 void i2c_del_mux_adapter(struct i2c_adapter *adap)
 {
 	struct i2c_mux_priv *priv = adap->algo_data;
+	char symlink_name[20];
+
+	snprintf(symlink_name, sizeof(symlink_name), "channel-%u", priv->chan_id);
+	sysfs_remove_link(&adap->dev.parent->kobj, symlink_name);
 
 	sysfs_remove_link(&priv->adap.dev.kobj, "mux_device");
 	i2c_del_adapter(adap);