[ZenCPU] AMD Zen CPU Backend with supported dtypes via zentorch weekly (#39967)

Signed-off-by: Chinmay Kulkarni <Chinmay.Kulkarni@amd.com>

setup.py

@@ -1085,7 +1085,9 @@ setup(
     install_requires=get_requirements(),
     extras_require={
         # AMD Zen CPU optimizations via zentorch
-        "zen": ["zentorch"],
+        "zen": [
+            "zentorch-weekly==5.2.1.dev20260408"
+        ],  # Zentorch has weekly releases. This pulls the known-good version.
         "bench": ["pandas", "matplotlib", "seaborn", "datasets", "scipy", "plotly"],
         "tensorizer": ["tensorizer==2.10.1"],
         "fastsafetensors": ["fastsafetensors >= 0.2.2"],

vllm/platforms/zen_cpu.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
+import torch
+
 from vllm.logger import init_logger
 from vllm.platforms.cpu import CpuPlatform
 
@@ -22,3 +24,9 @@ class ZenCpuPlatform(CpuPlatform):
     def is_zen_cpu(self) -> bool:
         # is_cpu() also returns True for this platform (inherited from CpuPlatform).
         return True
+
+    # Currently, AMD CPUs do not support float16 compute.
+    # Hence explicitly return bfloat16 and float32.
+    @property
+    def supported_dtypes(self) -> list[torch.dtype]:
+        return [torch.bfloat16, torch.float32]