Some Renesas controllers get into a weird state if they are reset while
programmed with 64bit addresses (they will preserve the top half of the
address in internal, non visible registers).

You end up with half the address coming from the kernel, and the other
half coming from the firmware.

Also, changing the programming leads to extra accesses even if the
controller is supposed to be halted. The controller ends up with a fatal
fault, and is then ripe for being properly reset. On the flip side,
this is completely unsafe if the defvice isn't behind an IOMMU, so
we have to make sure that this is the case. Can you say "broken"?

This is an alternative method to the one introduced in 8466489e
("xhci: Reset Renesas uPD72020x USB controller for 32-bit DMA issue"),
which will subsequently be removed.
Tested-by: Domenico Andreoli <domenico.andreoli@linux.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Tested-by: Faiz Abbas <faiz_abbas@ti.com>
Tested-by: Domenico Andreoli <domenico.andreoli@linux.com>
Acked-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>