ARM: mvebu: implement L2/PCIe deadlock workaround

ARM: mvebu: implement L2/PCIe deadlock workaround

The Marvell Armada 375 and Armada 38x SOCs, which use the Cortex-A9
CPU core, the PL310 cache and the Marvell PCIe hardware block are
affected a L2/PCIe deadlock caused by a system erratum when hardware
I/O coherency is used.

This deadlock can be avoided by mapping the PCIe memory areas as
strongly-ordered (note: MT_UNCACHED is strongly-ordered), and by
removing the outer cache sync done in software. This is implemented in
this patch by:

 * Registering a custom arch_ioremap_caller function that allows to
   make sure PCI memory regions are mapped MT_UNCACHED.

 * Adding at runtime the 'arm,io-coherent' property to the PL310 cache
   controller. This cannot be done permanently in the DT, because the
   hardware I/O coherency can only be enabled when CONFIG_SMP is
   enabled, in the current kernel situation.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Link: https://lkml.kernel.org/r/1400165974-9059-4-git-send-email-thomas.petazzoni@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>