Input: synaptics-rmi4 - avoid processing unknown IRQs

Input: synaptics-rmi4 - avoid processing unknown IRQs

rmi_process_interrupt_requests() calls handle_nested_irq() for
each interrupt status bit it finds. If the irq domain mapping for
this bit had not yet been set up, then it ends up calling
handle_nested_irq(0), which causes a NULL pointer dereference.

There's already code that masks the irq_status bits coming out of the
hardware with current_irq_mask, presumably to avoid this situation.
However current_irq_mask seems to more reflect the actual mask set
in the hardware rather than the IRQs software has set up and registered
for. For example, in rmi_driver_reset_handler(), the current_irq_mask
is initialized based on what is read from the hardware. If the reset
value of this mask enables IRQs that Linux has not set up yet, then
we end up in this situation.

There appears to be a third unused bitmask that used to serve this
purpose, fn_irq_bits. Use that bitmask instead of current_irq_mask
to avoid calling handle_nested_irq() on IRQs that have not yet been
set up.

Signed-off-by: Evan Green <evgreen@chromium.org>
Reviewed-by: Andrew Duggan <aduggan@synaptics.com>
Link: https://lore.kernel.org/r/20191008223657.163366-1-evgreen@chromium.org
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>