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The GIC architecture specification defines a set of registers
for redistributors and ITSes that control the sharebility and
cacheability attributes of redistributors/ITSes initiator ports
on the interconnect (GICR_[V]PROPBASER, GICR_[V]PENDBASER,
GITS_BASER<n>).

Architecturally the GIC provides a means to drive shareability
and cacheability attributes signals and related IWB/OWB/ISH barriers
but it is not mandatory for designs to wire up the corresponding
interconnect signals that control the cacheability/shareability
of transactions.

Redistributors and ITSes interconnect ports can be connected to
non-coherent interconnects that are not able to manage the
shareability/cacheability attributes; this implicitly makes
the redistributors and ITSes non-coherent observers.

So far, the GIC driver on probe executes a write to "probe" for
the redistributors and ITSes registers shareability bitfields
by writing a value (ie InnerShareable - the sh...