[MISC] correct DeviceConfig device field static type analysis (#19699)

Signed-off-by: Andy Xie <andy.xning@gmail.com>

Author: andyxning

vllm/config.py

@@ -2285,7 +2285,7 @@ def is_multi_step(self) -> bool:
 class DeviceConfig:
     """Configuration for the device to use for vLLM execution."""
 
-    device: SkipValidation[Union[Device, torch.device]] = "auto"
+    device: SkipValidation[Optional[Union[Device, torch.device]]] = "auto"
     """Device type for vLLM execution.
     This parameter is deprecated and will be
     removed in a future release.
@@ -2327,7 +2327,10 @@ def __post_init__(self):
                     "to turn on verbose logging to help debug the issue.")
         else:
             # Device type is assigned explicitly
-            self.device_type = self.device
+            if isinstance(self.device, str):
+                self.device_type = self.device
+            elif isinstance(self.device, torch.device):
+                self.device_type = self.device.type
 
         # Some device types require processing inputs on CPU
         if self.device_type in ["neuron"]:

vllm/engine/arg_utils.py

@@ -1018,7 +1018,8 @@ def create_engine_config(
         from vllm.platforms import current_platform
         current_platform.pre_register_and_update()
 
-        device_config = DeviceConfig(device=current_platform.device_type)
+        device_config = DeviceConfig(
+            device=cast(Device, current_platform.device_type))
         model_config = self.create_model_config()
 
         # * If VLLM_USE_V1 is unset, we enable V1 for "supported features"