ppc/pnv: add a helper to calculate MMIO addresses registers

Some controllers (ICP, PSI) have a base register address which is
calculated using the chip id.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

include/hw/ppc/pnv.h

@@ -91,14 +91,24 @@ typedef struct PnvChipClass {
     OBJECT_CHECK(PnvChip, (obj), TYPE_PNV_CHIP_POWER9)
 
 /*
- * This generates a HW chip id depending on an index:
+ * This generates a HW chip id depending on an index, as found on a
+ * two socket system with dual chip modules :
  *
  *    0x0, 0x1, 0x10, 0x11
  *
  * 4 chips should be the maximum
+ *
+ * TODO: use a machine property to define the chip ids
  */
 #define PNV_CHIP_HWID(i) ((((i) & 0x3e) << 3) | ((i) & 0x1))
 
+/*
+ * Converts back a HW chip id to an index. This is useful to calculate
+ * the MMIO addresses of some controllers which depend on the chip id.
+ */
+#define PNV_CHIP_INDEX(chip)                                    \
+    (((chip)->chip_id >> 2) * 2 + ((chip)->chip_id & 0x3))
+
 #define TYPE_POWERNV_MACHINE       MACHINE_TYPE_NAME("powernv")
 #define POWERNV_MACHINE(obj) \
     OBJECT_CHECK(PnvMachineState, (obj), TYPE_POWERNV_MACHINE)