Allow torchao quant to support quantization configs relying on module swap

Summary:
Current torchao integration quantizes the weights by wrapping weights
in a top level linear module and use quantize_ to quantize it, this works
for quantization methods that do inplace changes to the weight itself, such as
int4, float8, but there are quantization configs that would need module swap,
such as awq, that's not supported, in order to support these, we wrap the linear
in nn.Sequential so it is no longer a top level module and can be swapped to another module.

Test Plan:
uplodated an awq checkpoint: https://huggingface.co/torchao-testing/Phi-4-mini-instruct-int4wo-awq-0.13-dev
and we test by loading the checkpoint

```
python tests/quantization/test_torchao.py
```

Reviewers:

Subscribers:

Tasks:

Tags:
Signed-off-by: Jerry Zhang <[email protected]>

Author: jerryzh168

tests/quantization/test_torchao.py

@@ -75,5 +75,20 @@ def test_qwenvl_int8wo_model_loading_with_params(vllm_runner):
         print(output)
 
 
+@pytest.mark.skipif(not TORCHAO_AVAILABLE, reason="torchao is not available")
+def test_phi4mini_int4wo_awq_model_loading_with_params(vllm_runner):
+    torch._dynamo.reset()
+    model_name = "torchao-testing/Qwen3-4B-int4wo-awq-0.13-dev"
+    with vllm_runner(model_name=model_name,
+                     quantization="torchao",
+                     dtype="bfloat16",
+                     pt_load_map_location="cuda:0") as llm:
+        output = llm.generate_greedy(["The capital of France is"],
+                                     max_tokens=32)
+
+        assert output
+        print(output)
+
+
 if __name__ == "__main__":
     pytest.main([__file__])

vllm/model_executor/layers/quantization/torchao.py

@@ -152,18 +152,20 @@ def torchao_quantize_param_data(param: torch.Tensor,
     from torchao.quantization import quantize_
 
     assert isinstance(torchao_config, AOBaseConfig), f"{torchao_config}"
-    """ 
-    Avoid real weight allocation for faster load, since we will 
+    """
+    Avoid real weight allocation for faster load, since we will
     end up setting it to param.
     """
     with torch.device("meta"):
-        dummy_linear = torch.nn.Linear(param.shape[1],
-                                       param.shape[0],
-                                       bias=False)
+        # linear can't be top level module since quantize_ is inplace
+        # while some of our configs need to do module swap, and only non-top
+        # level modules support module swap
+        dummy_linear = torch.nn.Sequential(
+            torch.nn.Linear(param.shape[1], param.shape[0], bias=False))
 
-    dummy_linear.weight = param
+    dummy_linear[0].weight = param
     quantize_(dummy_linear, torchao_config)
-    return dummy_linear.weight
+    return dummy_linear[0].weight
 
 
 class TorchAOLinearMethod(LinearMethodBase):