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