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-rw-r--r--include/hw/misc/tz-ppc.h8
1 files changed, 7 insertions, 1 deletions
diff --git a/include/hw/misc/tz-ppc.h b/include/hw/misc/tz-ppc.h
index fc8b806e4d..080d6e2ec1 100644
--- a/include/hw/misc/tz-ppc.h
+++ b/include/hw/misc/tz-ppc.h
@@ -38,7 +38,13 @@
*
* QEMU interface:
* + sysbus MMIO regions 0..15: MemoryRegions defining the upstream end
- * of each of the 16 ports of the PPC
+ * of each of the 16 ports of the PPC. When a port is unused (i.e. no
+ * downstream MemoryRegion is connected to it) at the end of the 0..15
+ * range then no sysbus MMIO region is created for its upstream. When an
+ * unused port lies in the middle of the range with other used ports at
+ * higher port numbers, a dummy MMIO region is created to ensure that
+ * port N's upstream is always sysbus MMIO region N. Dummy regions should
+ * not be mapped, and will assert if any access is made to them.
* + Property "port[0..15]": MemoryRegion defining the downstream device(s)
* for each of the 16 ports of the PPC
* + Named GPIO inputs "cfg_nonsec[0..15]": set to 1 if the port should be