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-rw-r--r--arch/arm/mach-footbridge/include/mach/memory.h9
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/arm/mach-footbridge/include/mach/memory.h b/arch/arm/mach-footbridge/include/mach/memory.h
index 6ae2f1a07ab..cb16e59d87b 100644
--- a/arch/arm/mach-footbridge/include/mach/memory.h
+++ b/arch/arm/mach-footbridge/include/mach/memory.h
@@ -30,9 +30,18 @@
extern unsigned long __virt_to_bus(unsigned long);
extern unsigned long __bus_to_virt(unsigned long);
#endif
+#define __virt_to_bus __virt_to_bus
+#define __bus_to_virt __bus_to_virt
#elif defined(CONFIG_FOOTBRIDGE_HOST)
+/*
+ * The footbridge is programmed to expose the system RAM at the corresponding
+ * address. So, if PAGE_OFFSET is 0xc0000000, RAM appears at 0xe0000000.
+ * If 0x80000000, then its exposed at 0xa0000000 on the bus. etc.
+ * The only requirement is that the RAM isn't placed at bus address 0 which
+ * would clash with VGA cards.
+ */
#define __virt_to_bus(x) ((x) - 0xe0000000)
#define __bus_to_virt(x) ((x) + 0xe0000000)