GPIO expander user space access(ie. pca9552)

[Matt Barth]

Is there a defined process/interface to access GPIO expanders from user 
space to be able to determine when the state changes? Possibly polling a 
fd or getting notified on the state change?

Previously this was an i2c device that was accessed over i2c and the set 
of interested bits were simply read into the application. An example is 
the use of a pca9552 for presence detection on chassis fans.

Thanks,

Matt