mvebu: add a coherency fix which didn't make it to -stable, yet

Signed-off-by: Imre Kaloz <kaloz@openwrt.org>

SVN-Revision: 45024

target/linux/mvebu/patches-3.18/030-do_not_register_custom_DMA_operations_when_coherency_is_disabled.patch

@@ -0,0 +1,48 @@
+This patch is a partial backport of commit ef01c6c36bb8 ("ARM: mvebu:
+remove Armada 375 Z1 workaround for I/O coherency"). This commit was
+merged in v3.19, so kernel versions later than v3.19 are not affected
+by the problem that this commit fixes.
+
+It does not make a lot of sense to backport this commit entirely,
+since it is mainly removing some no longer useful code. However, this
+commit is also making sure that the bus_register_notifier that
+register the custom DMA operations that should be used for HW I/O
+coherency does not get registered when said HW I/O coherency is not
+enabled.
+
+This is particularly critical since we have decided to disable HW I/O
+coherency completely in all kernels < 4.0, to be on the safe side,
+while experimenting a new implementation of the HW I/O coherency in >=
+4.0.
+
+Without this commit, kernels earlier than 3.18 have the custom DMA
+operations normally used for HW I/O coherency registered (they don't
+do cache maintenance operations), while HW I/O coherency is
+disabled. It essentially causes every DMA transfer to transfer
+garbage.
+
+The issue fixed by this commit was introduced by 5ab5afd8ba83 ("ARM:
+mvebu: implement Armada 375 coherency workaround"), but it was not
+visible until now since it didn't cause any problem when HW I/O
+coherency is enabled.
+
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Cc: <stable@vger.kernel.org> v3.16..v3.18
+---
+ arch/arm/mach-mvebu/coherency.c | 5 +++--
+ 1 file changed, 3 insertions(+), 2 deletions(-)
+
+--- a/arch/arm/mach-mvebu/coherency.c
++++ b/arch/arm/mach-mvebu/coherency.c
+@@ -391,8 +391,9 @@ static int __init coherency_late_init(vo
+ 			armada_375_coherency_init_wa();
+ 	}
+ 
+-	bus_register_notifier(&platform_bus_type,
+-			      &mvebu_hwcc_nb);
++	if (coherency_available())
++		bus_register_notifier(&platform_bus_type,
++				      &mvebu_hwcc_nb);
+ 
+ 	return 0;
+ }