i2c/pca954x: Initialize the mux to disconnected state
authorPetri Gynther <pgynther@google.com>
Wed, 29 Jun 2011 09:36:11 +0000 (11:36 +0200)
committerJean Delvare <khali@endymion.delvare>
Wed, 29 Jun 2011 09:36:11 +0000 (11:36 +0200)
commitcd823db8b1161ef0d756514d280715a576d65cc3
tree96eb9acd38c9206be203219023df5bde4700ce88
parent9b640f2e154268cb516efcaf9c434f2e73c6783e
i2c/pca954x: Initialize the mux to disconnected state

pca954x power-on default is channel 0 connected. If multiple pca954x
muxes are connected to the same physical I2C bus, the parent bus will
see channel 0 devices behind both muxes by default. This is bad.

Scenario:
            -- pca954x @ 0x70 -- ch 0 (I2C-bus-101) -- EEPROM @ 0x50
            |
I2C-bus-1 ---
            |
            -- pca954x @ 0x71 -- ch 0 (I2C-bus-111) -- EEPROM @ 0x50

1. Load I2C bus driver: creates I2C-bus-1
2. Load pca954x driver: creates virtual I2C-bus-101 and I2C-bus-111
3. Load eeprom driver
4. Try to read EEPROM @ 0x50 on I2C-bus-101. The transaction will also bleed
   onto I2C-bus-111 because pca954x @ 0x71 channel 0 is connected by default.

Fix: Initialize pca954x to disconnected state in pca954x_probe()

Signed-off-by: Petri Gynther <pgynther@google.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: stable@kernel.org
drivers/i2c/muxes/pca954x.c