diff --git a/hw/misc/allwinner-r40-dramc.c b/hw/misc/allwinner-r40-dramc.c
index 2cc0254a55..3d81ddb2e1 100644
--- a/hw/misc/allwinner-r40-dramc.c
+++ b/hw/misc/allwinner-r40-dramc.c
@@ -414,7 +414,6 @@ static void allwinner_r40_dramc_reset(DeviceState *dev)
 static void allwinner_r40_dramc_realize(DeviceState *dev, Error **errp)
 {
     AwR40DramCtlState *s = AW_R40_DRAMC(dev);
-    SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
 
     if (!get_match_ddr(s->ram_size)) {
         error_report("%s: ram-size %u MiB is not supported",
@@ -422,23 +421,23 @@ static void allwinner_r40_dramc_realize(DeviceState *dev, Error **errp)
         exit(1);
     }
 
-    /* R40 support max 2G memory but we only support up to 1G now. index 3 */
+    /* R40 support max 2G memory but we only support up to 1G now. */
     memory_region_init_io(&s->detect_cells, OBJECT(s),
                           &allwinner_r40_detect_ops, s,
                           "DRAMCELLS", 1 * GiB);
-    sysbus_init_mmio(sbd, &s->detect_cells);
-    sysbus_mmio_map_overlap(sbd, 3, s->ram_addr, 10);
+    memory_region_add_subregion_overlap(get_system_memory(), s->ram_addr,
+                                        &s->detect_cells, 10);
     memory_region_set_enabled(&s->detect_cells, false);
 
     /*
      * We only support DRAM size up to 1G now, so prepare a high memory page
-     * after 1G for dualrank detect. index = 4
+     * after 1G for dualrank detect.
      */
     memory_region_init_io(&s->dram_high, OBJECT(s),
                             &allwinner_r40_dualrank_detect_ops, s,
                             "DRAMHIGH", KiB);
-    sysbus_init_mmio(SYS_BUS_DEVICE(s), &s->dram_high);
-    sysbus_mmio_map(SYS_BUS_DEVICE(s), 4, s->ram_addr + GiB);
+    memory_region_add_subregion(get_system_memory(), s->ram_addr + GiB,
+                                &s->dram_high);
 }
 
 static void allwinner_r40_dramc_init(Object *obj)