ARM: mvebu: completely disable hardware I/O coherency

The current hardware I/O coherency is known to cause problems with DMA
coherent buffers, as it still requires explicit I/O synchronization
barriers, which is not compatible with the semantics expected by the
Linux DMA coherent buffers API.

So, in order to have enough time to validate a new solution based on
automatic I/O synchronization barriers, this commit disables hardware
I/O coherency entirely. Future patches will re-enable it.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: <stable@vger.kernel.org> # v3.8+
Signed-off-by: Andrew Lunn <andrew@lunn.ch>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/arm/mach-mvebu/coherency.c b/arch/arm/mach-mvebu/coherency.c
index 3585cb394e9b..caa21e9b8cd9 100644
--- a/arch/arm/mach-mvebu/coherency.c
+++ b/arch/arm/mach-mvebu/coherency.c
@@ -246,9 +246,14 @@ static int coherency_type(void)
         return type;
 }
 
+/*
+ * As a precaution, we currently completely disable hardware I/O
+ * coherency, until enough testing is done with automatic I/O
+ * synchronization barriers to validate that it is a proper solution.
+ */
 int coherency_available(void)
 {
-        return coherency_type() != COHERENCY_FABRIC_TYPE_NONE;
+        return false;
 }
 
 int __init coherency_init(void)