What:		/sys/bus/i2c/.../idle_state
Date:		January 2019
KernelVersion:	5.2
Contact:	Robert Shearman <robert.shearman@att.com>
Description:
		Value that exists only for mux devices that can be
		written to control the behaviour of the multiplexer on
		idle. Possible values:

		===========  ===============================================
		-2	     disconnect on idle, i.e. deselect the last used
			     channel, which is useful when there is a device
			     with an address that conflicts with another
			     device on another mux on the same parent bus.
		-1	     leave the mux as-is, which is the most optimal
			     setting in terms of I2C operations and is the
			     default mode.
		0..<nchans>  set the mux to a predetermined channel,
			     which is useful if there is one channel that is
			     used almost always, and you want to reduce the
			     latency for normal operations after rare
			     transactions on other channels
		===========  ===============================================
