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: NPetri Gynther <pgynther@google.com>
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Cc: stable@kernel.org

Add an i2c mux driver providing access to i2c bus segments using a
hardware MUX sitting on a master bus and controlled through gpio pins.

E.G. something like:

  ----------              ----------  Bus segment 1   - - - - -
 |          | SCL/SDA    |          |-------------- |           |
 |          |------------|          |
 |          |            |          | Bus segment 2 |           |
 |  Linux   | GPIO 1..N  |   MUX    |---------------   Devices
 |          |------------|          |               |           |
 |          |            |          | Bus segment M
 |          |            |          |---------------|           |
  ----------              ----------                  - - - - -

SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M
according to the settings of the GPIO pins 1..N.
Signed-off-by: NPeter Korsgaard <peter.korsgaard@barco.com>
Signed-off-by: NJean Delvare <khali@linux-fr.org>

The underlying I2C adapter may or may not be present when this driver
gets initialized, and may disappear later, so there is no safe time at
which the probe and remove functions can be discarded.
Signed-off-by: NGuenter Roeck <guenter.roeck@ericsson.com>
Signed-off-by: NJean Delvare <khali@linux-fr.org>

This patch adds support for PCA9541, an I2C Bus Master Selector.
The driver is modeled as single channel I2C Multiplexer to be able to utilize
the I2C multiplexer framework.
Signed-off-by: NGuenter Roeck <guenter.roeck@ericsson.com>
Reviewed-by: NTom Grennan <tom.grennan@ericsson.com>
Acked-by: NJean Delvare <khali@linux-fr.org>

Replace EXTRA_CFLAGS with ccflags-y.
Signed-off-by: Nmatt mooney <mfm@muteddisk.com>
Signed-off-by: NJean Delvare <khali@linux-fr.org>

I2C driver for PCA954x I2C multiplexer series.
Signed-off-by: NMichael Lawnick <ml.lawnick@gmx.de>
Acked-by: NRodolfo Giometti <giometti@linux.it>
Signed-off-by: NJean Delvare <khali@linux-fr.org>