What:		/sys/devices/platform/<i2c-demux-name>/cur_master
Date:		January 2016
KernelVersion:	4.6
Contact:	Wolfram Sang <wsa@the-dreams.de>
Description:

This file selects the active I2C master for a demultiplexed bus.

Write 0 there for the first master, 1 for the second etc. Reading the file will
give you a list with the active master marked. Example from a Renesas Lager
board:

root@Lager:~# cat /sys/devices/platform/i2c@8/cur_master
* 0 - /i2c@9
  1 - /i2c@e6520000
  2 - /i2c@e6530000

root@Lager:~# echo 2 > /sys/devices/platform/i2c@8/cur_master

root@Lager:~# cat /sys/devices/platform/i2c@8/cur_master
  0 - /i2c@9
  1 - /i2c@e6520000
* 2 - /i2c@e6530000