diff --git a/hw/misc/aspeed_sdmc.c b/hw/misc/aspeed_sdmc.c
index 0df008e52a..24fd4aee2d 100644
--- a/hw/misc/aspeed_sdmc.c
+++ b/hw/misc/aspeed_sdmc.c
@@ -126,10 +126,12 @@ static void aspeed_sdmc_write(void *opaque, hwaddr addr, uint64_t data,
         case AST2400_A0_SILICON_REV:
         case AST2400_A1_SILICON_REV:
             data &= ~ASPEED_SDMC_READONLY_MASK;
+            data |= s->fixed_conf;
             break;
         case AST2500_A0_SILICON_REV:
         case AST2500_A1_SILICON_REV:
             data &= ~ASPEED_SDMC_AST2500_READONLY_MASK;
+            data |= s->fixed_conf;
             break;
         default:
             g_assert_not_reached();
@@ -198,25 +200,7 @@ static void aspeed_sdmc_reset(DeviceState *dev)
     memset(s->regs, 0, sizeof(s->regs));
 
     /* Set ram size bit and defaults values */
-    switch (s->silicon_rev) {
-    case AST2400_A0_SILICON_REV:
-    case AST2400_A1_SILICON_REV:
-        s->regs[R_CONF] |=
-            ASPEED_SDMC_VGA_COMPAT |
-            ASPEED_SDMC_DRAM_SIZE(s->ram_bits);
-        break;
-
-    case AST2500_A0_SILICON_REV:
-    case AST2500_A1_SILICON_REV:
-        s->regs[R_CONF] |=
-            ASPEED_SDMC_HW_VERSION(1) |
-            ASPEED_SDMC_VGA_APERTURE(ASPEED_SDMC_VGA_64MB) |
-            ASPEED_SDMC_DRAM_SIZE(s->ram_bits);
-        break;
-
-    default:
-        g_assert_not_reached();
-    }
+    s->regs[R_CONF] = s->fixed_conf;
 }
 
 static void aspeed_sdmc_realize(DeviceState *dev, Error **errp)
@@ -234,10 +218,15 @@ static void aspeed_sdmc_realize(DeviceState *dev, Error **errp)
     case AST2400_A0_SILICON_REV:
     case AST2400_A1_SILICON_REV:
         s->ram_bits = ast2400_rambits(s);
+        s->fixed_conf = ASPEED_SDMC_VGA_COMPAT |
+            ASPEED_SDMC_DRAM_SIZE(s->ram_bits);
         break;
     case AST2500_A0_SILICON_REV:
     case AST2500_A1_SILICON_REV:
         s->ram_bits = ast2500_rambits(s);
+        s->fixed_conf = ASPEED_SDMC_HW_VERSION(1) |
+            ASPEED_SDMC_VGA_APERTURE(ASPEED_SDMC_VGA_64MB) |
+            ASPEED_SDMC_DRAM_SIZE(s->ram_bits);
         break;
     default:
         g_assert_not_reached();
diff --git a/include/hw/misc/aspeed_sdmc.h b/include/hw/misc/aspeed_sdmc.h
index 682f0f5d56..e079c66a7d 100644
--- a/include/hw/misc/aspeed_sdmc.h
+++ b/include/hw/misc/aspeed_sdmc.h
@@ -27,6 +27,7 @@ typedef struct AspeedSDMCState {
     uint32_t silicon_rev;
     uint32_t ram_bits;
     uint64_t ram_size;
+    uint32_t fixed_conf;
 
 } AspeedSDMCState;