[config] Expose `get_total_num_hidden_layers()` in ModelConfig (#28961)

Signed-off-by: tovam <tovam@pliops.com>
Co-authored-by: Wentao Ye <44945378+yewentao256@users.noreply.github.com>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>

vllm/config/model.py

@@ -1369,11 +1369,7 @@ class ModelConfig:
         # Coerce to 0 if explicitly set to None
         return num_experts or 0
 
-    def get_layers_start_end_indices(
-        self, parallel_config: ParallelConfig
-    ) -> tuple[int, int]:
-        from vllm.distributed.utils import get_pp_indices
-
+    def get_total_num_hidden_layers(self) -> int:
         if (
             self.hf_text_config.model_type == "deepseek_mtp"
             or self.hf_config.model_type == "mimo_mtp"
@@ -1393,6 +1389,15 @@ class ModelConfig:
             total_num_hidden_layers = getattr(
                 self.hf_text_config, "num_hidden_layers", 0
             )
+        return total_num_hidden_layers
+
+    def get_layers_start_end_indices(
+        self, parallel_config: ParallelConfig
+    ) -> tuple[int, int]:
+        from vllm.distributed.utils import get_pp_indices
+
+        total_num_hidden_layers = self.get_total_num_hidden_layers()
+
         # the layout order is: DP x PP x TP
         pp_rank = (
             parallel_config.rank // parallel_config.tensor_parallel_size