Add BCM2708 mailbox definitions and implementation.

The mailbox is used to communicate with the VideoCore on the rPi for
various tasks. First it will be used to configure the framebuffer.

headers/private/kernel/arch/arm/bcm2708.h

@@ -40,6 +40,18 @@
 #define BCM2708_SDRAM_BASE		0x00000000
 #define BCM2708_PERIPHERAL_BASE	0x20000000
 
+// Added to physical addresses to select the different cache behaviours
+#define BCM2708_VIDEO_CORE_L1_L2_CACHED		(0 << 30)
+#define BCM2708_VIDEO_CORE_L2_COHERENT		(1 << 30)
+#define BCM2708_VIDEO_CORE_L2_CACHED		(2 << 30)
+#define BCM2708_VIDEO_CORE_UNCACHED			(3 << 30)
+
+// The highest two bits are used to select aliases to the physical memory
+// with different cache semantic. Clearing them converts the address to
+// physical memory as seen by ARM.
+#define BCM2708_BUS_TO_PHYSICAL(x)			(x & ~BCM2708_VIDEO_CORE_UNCACHED)
+
+
 #define ST_BASE			0x3000
 	// System Timer, sec 12.0, page 172
 #define DMA_BASE		0x7000
@@ -122,4 +134,19 @@
 #define UART_SYSC   20
 
 
+/* Mailbox */
+#define ARM_CTRL_0_MAILBOX_BASE				(ARM_CTRL_0_SBM_BASE + 0x80)
+
+#define ARM_MAILBOX_READ					0x00
+#define ARM_MAILBOX_STATUS					0x18
+#define ARM_MAILBOX_WRITE					0x20
+
+#define ARM_MAILBOX_FULL					(1 << 31)
+#define ARM_MAILBOX_EMPTY					(1 << 30)
+
+#define ARM_MAILBOX_DATA_MASK				0xfffffff0
+#define ARM_MAILBOX_CHANNEL_MASK			0x0000000f
+
+#define ARM_MAILBOX_CHANNEL_FRAMEBUFFER		1
+
 #endif /* __PLATFORM_BCM2708_H */