[ARM] remove a common set of __virt_to_bus definitions

Let's provide an overridable default instead of having every machine
class define __virt_to_bus and __bus_to_virt to the same thing.  What
most platforms are using is bus_addr == phys_addr so such is the default.

One exception is ebsa110 which has no DMA what so ever, so the actual
definition is not important except only for proper compilation.  Also
added a comment about the special footbridge bus translation.

Let's also remove comments alluding to set_dma_addr which is not
(and should not) be commonly used.

Signed-off-by: Nicolas Pitre <nico@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

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)