diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
index 354fae8e2e0b..2239bbc66caf 100644
--- a/drivers/gpu/drm/i915/display/intel_bios.c
+++ b/drivers/gpu/drm/i915/display/intel_bios.c
@@ -2785,27 +2785,35 @@ static void parse_ddi_ports(struct drm_i915_private *i915)
 	}
 }
 
+static int child_device_expected_size(u16 version)
+{
+	BUILD_BUG_ON(sizeof(struct child_device_config) < 40);
+
+	if (version > 256)
+		return -ENOENT;
+	else if (version >= 256)
+		return 40;
+	else if (version >= 216)
+		return 39;
+	else if (version >= 196)
+		return 38;
+	else if (version >= 195)
+		return 37;
+	else if (version >= 111)
+		return LEGACY_CHILD_DEVICE_CONFIG_SIZE;
+	else if (version >= 106)
+		return 27;
+	else
+		return 22;
+}
+
 static bool child_device_size_valid(struct drm_i915_private *i915, int size)
 {
 	int expected_size;
 
-	if (i915->display.vbt.version < 106) {
-		expected_size = 22;
-	} else if (i915->display.vbt.version < 111) {
-		expected_size = 27;
-	} else if (i915->display.vbt.version < 195) {
-		expected_size = LEGACY_CHILD_DEVICE_CONFIG_SIZE;
-	} else if (i915->display.vbt.version == 195) {
-		expected_size = 37;
-	} else if (i915->display.vbt.version <= 215) {
-		expected_size = 38;
-	} else if (i915->display.vbt.version <= 255) {
-		expected_size = 39;
-	} else if (i915->display.vbt.version <= 256) {
-		expected_size = 40;
-	} else {
+	expected_size = child_device_expected_size(i915->display.vbt.version);
+	if (expected_size < 0) {
 		expected_size = sizeof(struct child_device_config);
-		BUILD_BUG_ON(sizeof(struct child_device_config) < 40);
 		drm_dbg(&i915->drm,
 			"Expected child device config size for VBT version %u not known; assuming %d\n",
 			i915->display.vbt.version, expected_size);