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 6ae2f1a07ab9..cb16e59d87b6 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)