[PATCH] ARM: mvebu: don't set the PL310 in I/O coherency mode when I/O coherency is disabled

[Thomas Petazzoni]

Since commit f2c3c67f00 (merge commit that adds commit "ARM: mvebu:
completely disable hardware I/O coherency"), we disable I/O coherency
on Armada EBU platforms.

However, we continue to initialize the coherency fabric, because this
coherency fabric is needed on Armada XP for inter-CPU
coherency. Unfortunately, due to this, we also continued to execute
the coherency fabric initialization code for Armada 375/38x, which
switched the PL310 into I/O coherent mode. This has the effect of
disabling the outer cache sync operation: this is needed when I/O
coherency is enabled to work around a PCIe/L2 deadlock. But obviously,
when I/O coherency is disabled, having the outer cache sync operation
is crucial.

Therefore, this commit fixes the armada_375_380_coherency_init() so
that the PL310 is switched to I/O coherent mode only if I/O coherency
is enabled.

Without this fix, all devices using DMA are broken on Armada 375/38x.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
Cc: <stable at vger.kernel.org>
---
This fix is needed in 3.19-rc, and in all stable kernel releases in
which f2c3c67f00 was added.

In mainline, it is not strictly needed, since we have since then
re-enabled I/O coherency using automatic barriers.

Commit applies on top of 3.19-rc6, and has been tested on Armada XP,
Armada 375 and Armada 38x, by checking that the XOR engine self-tests
are working properly, which is a good indication that DMA and I/O
coherency is minimally working. Without the fix, the XOR engine
self-tests were not even working on Armada 38x.

 arch/arm/mach-mvebu/coherency.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm/mach-mvebu/coherency.c b/arch/arm/mach-mvebu/coherency.c
index caa21e9..ccef880 100644
--- a/arch/arm/mach-mvebu/coherency.c
+++ b/arch/arm/mach-mvebu/coherency.c
@@ -190,6 +190,13 @@ static void __init armada_375_380_coherency_init(struct device_node *np)
 	arch_ioremap_caller = armada_pcie_wa_ioremap_caller;
 
 	/*
+	 * We should switch the PL310 to I/O coherency mode only if
+	 * I/O coherency is actually enabled.
+	 */
+	if (!coherency_available())
+		return;
+
+	/*
 	 * Add the PL310 property "arm,io-coherent". This makes sure the
 	 * outer sync operation is not used, which allows to
 	 * workaround the system erratum that causes deadlocks when
-- 
2.1.0