2 files changed, 20 insertions, 0 deletions
diff --git a/memory.c b/memory.c
index 5f2c9efa2a..7dd7cacf04 100644
--- a/memory.c
+++ b/memory.c
@@ -14,6 +14,7 @@
 #include "memory.h"
 #include "exec-memory.h"
 #include "ioport.h"
+#include "bitops.h"
 #include <assert.h>
 
 typedef struct AddrRange AddrRange;
@@ -506,6 +507,10 @@ static uint32_t memory_region_read_thunk_n(void *_mr,
         return -1U; /* FIXME: better signalling */
     }
 
+    if (!mr->ops->read) {
+        return mr->ops->old_mmio.read[bitops_ffsl(size)](mr->opaque, addr);
+    }
+
     /* FIXME: support unaligned access */
 
     access_size_min = mr->ops->impl.min_access_size;
@@ -542,6 +547,11 @@ static void memory_region_write_thunk_n(void *_mr,
         return; /* FIXME: better signalling */
     }
 
+    if (!mr->ops->write) {
+        mr->ops->old_mmio.write[bitops_ffsl(size)](mr->opaque, addr, data);
+        return;
+    }
+
     /* FIXME: support unaligned access */
 
     access_size_min = mr->ops->impl.min_access_size;
diff --git a/memory.h b/memory.h
index 40ab95a98c..003c999219 100644
--- a/memory.h
+++ b/memory.h
@@ -28,6 +28,7 @@
 typedef struct MemoryRegionOps MemoryRegionOps;
 typedef struct MemoryRegion MemoryRegion;
 typedef struct MemoryRegionPortio MemoryRegionPortio;
+typedef struct MemoryRegionMmio MemoryRegionMmio;
 
 /* Must match *_DIRTY_FLAGS in cpu-all.h.  To be replaced with dynamic
  * registration.
@@ -36,6 +37,11 @@ typedef struct MemoryRegionPortio MemoryRegionPortio;
 #define DIRTY_MEMORY_CODE      1
 #define DIRTY_MEMORY_MIGRATION 3
 
+struct MemoryRegionMmio {
+    CPUReadMemoryFunc *read[3];
+    CPUWriteMemoryFunc *write[3];
+};
+
 /*
  * Memory region callbacks
  */
@@ -85,6 +91,10 @@ struct MemoryRegionOps {
      * backwards compatibility with old portio registration
      */
     const MemoryRegionPortio *old_portio;
+    /* If .read and .write are not present, old_mmio may be used for
+     * backwards compatibility with old mmio registration
+     */
+    const MemoryRegionMmio old_mmio;
 };
 
 typedef struct CoalescedMemoryRange CoalescedMemoryRange;