memory: Provide memory_region_init_rom()

Provide a new helper function memory_region_init_rom() for memory
regions which are read-only (and unlike those created by
memory_region_init_rom_device() don't have special behaviour
for writes). This has the same behaviour as calling
memory_region_init_ram() and then memory_region_set_readonly()
(which is what we do today in boards with pure ROMs) but is a
more easily discoverable API for the purpose.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1467122287-24974-2-git-send-email-peter.maydell@linaro.org

docs/memory.txt

@@ -41,8 +41,13 @@ MemoryRegion):
   MemoryRegionOps structure describing the callbacks.
 
 - ROM: a ROM memory region works like RAM for reads (directly accessing
-  a region of host memory), but like MMIO for writes (invoking a callback).
-  You initialize these with memory_region_init_rom_device().
+  a region of host memory), and forbids writes. You initialize these with
+  memory_region_init_rom().
+
+- ROM device: a ROM device memory region works like RAM for reads
+  (directly accessing a region of host memory), but like MMIO for
+  writes (invoking a callback).  You initialize these with
+  memory_region_init_rom_device().
 
 - IOMMU region: an IOMMU region translates addresses of accesses made to it
   and forwards them to some other target memory region.  As the name suggests,

include/exec/memory.h

@@ -444,6 +444,25 @@ void memory_region_init_alias(MemoryRegion *mr,
                               hwaddr offset,
                               uint64_t size);
 
+/**
+ * memory_region_init_rom: Initialize a ROM memory region.
+ *
+ * This has the same effect as calling memory_region_init_ram()
+ * and then marking the resulting region read-only with
+ * memory_region_set_readonly().
+ *
+ * @mr: the #MemoryRegion to be initialized.
+ * @owner: the object that tracks the region's reference count
+ * @name: the name of the region.
+ * @size: size of the region.
+ * @errp: pointer to Error*, to store an error if it happens.
+ */
+void memory_region_init_rom(MemoryRegion *mr,
+                            struct Object *owner,
+                            const char *name,
+                            uint64_t size,
+                            Error **errp);
+
 /**
  * memory_region_init_rom_device:  Initialize a ROM memory region.  Writes are
  *                                 handled via callbacks.

memory.c

@@ -1376,6 +1376,21 @@ void memory_region_init_alias(MemoryRegion *mr,
     mr->alias_offset = offset;
 }
 
+void memory_region_init_rom(MemoryRegion *mr,
+                            struct Object *owner,
+                            const char *name,
+                            uint64_t size,
+                            Error **errp)
+{
+    memory_region_init(mr, owner, name, size);
+    mr->ram = true;
+    mr->readonly = true;
+    mr->terminates = true;
+    mr->destructor = memory_region_destructor_ram;
+    mr->ram_block = qemu_ram_alloc(size, mr, errp);
+    mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
+}
+
 void memory_region_init_rom_device(MemoryRegion *mr,
                                    Object *owner,
                                    const MemoryRegionOps *ops,