[PATCH] i2c: mux: create proper topology in sysfs

[Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>]

The current implementation creates muxed i2c-<n> busses as immediate
children of their i2c-<n> parent bus. In case of multiple muxes on one
bus, it is impossible to determine which muxed bus comes from which mux.

Change the topology so that they are created under the corresponding mux
device. This way, multiple muxes on the same segment can coexist and
children busses are grouped accordingly.

So for instance, by adding a pca9547 device with address 0x70 to
bus i2c-0, instead of:

/sys/class/i2c-dev/i2c-0/device/i2c-1
...
/sys/class/i2c-dev/i2c-0/device/i2c-8

we get:

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

Symlinks for backward compatibility are provided.

Signed-off-by: Gerlando Falauto <gerlando.falauto-SkAbAL50j+5BDgjK7y7TUQ@public.gmane.org>

[wsa: Ported to top-of-tree (1 line left :)) and added the compatibility
links.]
Signed-off-by: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
Cc: Jean Delvare <jdelvare-l3A5Bk7waGM@public.gmane.org>
Cc: Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>
Cc: Martin Belanger <martin.belanger-Ir6+u9MVKBtBDgjK7y7TUQ@public.gmane.org>
Cc: Rodolfo Giometti <giometti-AVVDYK/kqiJWk0Htik3J/w@public.gmane.org>
Cc: Michael Lawnick <ml.lawnick-Mmb7MZpHnFY@public.gmane.org>
Cc: Jeroen De Wachter <jeroen.de.wachter-CNXmb7IdZIWZIoH1IeqzKA@public.gmane.org>
---

So, this is what I came up with to fix the mux-topology problem. Since I don't
really use muxes, please review/comment/test. And give Acks/Tested-by tags if
this works for you.

 drivers/i2c/i2c-mux.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 2d0847b6be62..5b482ea32faf 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -138,7 +138,7 @@ struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
 	priv->adap.owner = THIS_MODULE;
 	priv->adap.algo = &priv->algo;
 	priv->adap.algo_data = priv;
-	priv->adap.dev.parent = &parent->dev;
+	priv->adap.dev.parent = mux_dev;
 	priv->adap.retries = parent->retries;
 	priv->adap.timeout = parent->timeout;
 
@@ -183,6 +183,9 @@ struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
 		return NULL;
 	}
 
+	WARN(sysfs_create_link(&parent->dev.kobj, &priv->adap.dev.kobj, priv->adap.dev.kobj.name),
+				"can't create compatibility link for old mux name scheme\n");
+
 	dev_info(&parent->dev, "Added multiplexed i2c bus %d\n",
 		 i2c_adapter_id(&priv->adap));
 
@@ -194,6 +197,7 @@ void i2c_del_mux_adapter(struct i2c_adapter *adap)
 {
 	struct i2c_mux_priv *priv = adap->algo_data;
 
+	sysfs_remove_link(&priv->parent->dev.kobj, adap->dev.kobj.name);
 	i2c_del_adapter(adap);
 	kfree(priv);
 }
-- 
2.1.1