memory: introduce memory_region_present

This new API will avoid having too many memory_region_ref/unref
in paths that currently use memory_region_find.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/acpi/piix4.c

@@ -388,10 +388,10 @@ static void piix4_pm_machine_ready(Notifier *n, void *opaque)
 
     pci_conf = s->dev.config;
     pci_conf[0x5f] = 0x10 |
-        (memory_region_find(io_as, 0x378, 1).mr ? 0x80 : 0);
+        (memory_region_present(io_as, 0x378) ? 0x80 : 0);
     pci_conf[0x63] = 0x60;
-    pci_conf[0x67] = (memory_region_find(io_as, 0x3f8, 1).mr ? 0x08 : 0) |
-        (memory_region_find(io_as, 0x2f8, 1).mr ? 0x90 : 0);
+    pci_conf[0x67] = (memory_region_present(io_as, 0x3f8) ? 0x08 : 0) |
+        (memory_region_present(io_as, 0x2f8) ? 0x90 : 0);
 }
 
 static int piix4_pm_initfn(PCIDevice *dev)

hw/isa/lpc_ich9.c

@@ -481,19 +481,19 @@ static void ich9_lpc_machine_ready(Notifier *n, void *opaque)
     uint8_t *pci_conf;
 
     pci_conf = s->d.config;
-    if (memory_region_find(io_as, 0x3f8, 1).mr) {
+    if (memory_region_present(io_as, 0x3f8)) {
         /* com1 */
         pci_conf[0x82] |= 0x01;
     }
-    if (memory_region_find(io_as, 0x2f8, 1).mr) {
+    if (memory_region_present(io_as, 0x2f8)) {
         /* com2 */
         pci_conf[0x82] |= 0x02;
     }
-    if (memory_region_find(io_as, 0x378, 1).mr) {
+    if (memory_region_present(io_as, 0x378)) {
         /* lpt */
         pci_conf[0x82] |= 0x04;
     }
-    if (memory_region_find(io_as, 0x3f0, 1).mr) {
+    if (memory_region_present(io_as, 0x3f0)) {
         /* floppy */
         pci_conf[0x82] |= 0x08;
     }

include/exec/memory.h

@@ -836,6 +836,18 @@ void memory_region_set_address(MemoryRegion *mr, hwaddr addr);
 void memory_region_set_alias_offset(MemoryRegion *mr,
                                     hwaddr offset);
 
+/**
+ * memory_region_present: translate an address/size relative to a
+ * MemoryRegion into a #MemoryRegionSection.
+ *
+ * Answer whether a #MemoryRegion within @parent covers the address
+ * @addr.
+ *
+ * @parent: a MemoryRegion within which @addr is a relative address
+ * @addr: the area within @parent to be searched
+ */
+bool memory_region_present(MemoryRegion *parent, hwaddr addr);
+
 /**
  * memory_region_find: translate an address/size relative to a
  * MemoryRegion into a #MemoryRegionSection.

memory.c

@@ -1478,6 +1478,15 @@ static FlatRange *address_space_lookup(AddressSpace *as, AddrRange addr)
                    sizeof(FlatRange), cmp_flatrange_addr);
 }
 
+bool memory_region_present(MemoryRegion *parent, hwaddr addr)
+{
+    MemoryRegion *mr = memory_region_find(parent, addr, 1).mr;
+    if (!mr) {
+        return false;
+    }
+    return true;
+}
+
 MemoryRegionSection memory_region_find(MemoryRegion *mr,
                                        hwaddr addr, uint64_t size)
 {