I originally overlooked a couple flag bits defined in the fdt binding docs.
One flag suppresses the pad configuration (pullup/pulldown/etc). The other
one requires that the SION (set input on) flag be set in the mux register.
Also, it appears from the data involved that if the input register
address in the config tuple is zero, there is no input configuration. The
old code was writing to register zero, which contains a collection of misc
control bits (having nothing to do with input configuration) that probably
shouldn't get overwritten arbitrarily. The bindings doc doesn't explictly
mention this.
3a8af166a2