[ARM] 3439/2: xsc3: add I/O coherency support

Patch from Lennert Buytenhek

This patch adds support for the I/O coherent cache available on the
xsc3.  The approach is to provide a simple API to determine whether the
chipset supports coherency by calling arch_is_coherent() and then
setting the appropriate system memory PTE and PMD bits.  In addition,
we call this API on dma_alloc_coherent() and dma_map_single() calls.
A generic version exists that will compile out all the coherency-related
code that is not needed on the majority of ARM systems.

Note that we do not check for coherency in the dma_alloc_writecombine()
function as that still requires a special PTE setting.  We also don't
touch dma_mmap_coherent() as that is a special ARM-only API that is by
definition only used on non-coherent system.

Signed-off-by: Deepak Saxena <dsaxena@plexity.net>
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/asm-arm/memory.h b/include/asm-arm/memory.h
index afa5c3e..2b3cf69 100644
--- a/include/asm-arm/memory.h
+++ b/include/asm-arm/memory.h
@@ -234,6 +234,14 @@ static inline __deprecated void *bus_to_virt(unsigned long x)
 #define virt_to_dma(dev, addr)		(__arch_virt_to_dma(dev, addr))
 #endif
 
+/*
+ * Optional coherency support.  Currently used only by selected
+ * Intel XSC3-based systems.
+ */
+#ifndef arch_is_coherent
+#define arch_is_coherent()		0
+#endif
+
 #endif
 
 #include <asm-generic/memory_model.h>