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+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