[TPU] Support Pathways in vLLM (#21417)

Signed-off-by: wenxindongwork <wenxindong@google.com>

vllm/envs.py

@@ -124,6 +124,7 @@ if TYPE_CHECKING:
     VLLM_V1_USE_OUTLINES_CACHE: bool = False
     VLLM_TPU_BUCKET_PADDING_GAP: int = 0
     VLLM_TPU_MOST_MODEL_LEN: Optional[int] = None
+    VLLM_TPU_USING_PATHWAYS: bool = False
     VLLM_USE_DEEP_GEMM: bool = False
     VLLM_USE_FLASHINFER_MOE_FP8: bool = False
     VLLM_USE_FLASHINFER_MOE_FP4: bool = False
@@ -900,6 +901,10 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "VLLM_TPU_MOST_MODEL_LEN":
     lambda: maybe_convert_int(os.environ.get("VLLM_TPU_MOST_MODEL_LEN", None)),
 
+    # Whether using Pathways
+    "VLLM_TPU_USING_PATHWAYS":
+    lambda: bool("proxy" in os.getenv("JAX_PLATFORMS", "").lower()),
+
     # Allow use of DeepGemm kernels for fused moe ops.
     "VLLM_USE_DEEP_GEMM":
     lambda: bool(int(os.getenv("VLLM_USE_DEEP_GEMM", "0"))),

vllm/platforms/__init__.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
-
 import logging
 import traceback
 from itertools import chain
 from typing import TYPE_CHECKING, Optional
 
+from vllm import envs
 from vllm.plugins import load_plugins_by_group
 from vllm.utils import resolve_obj_by_qualname, supports_xccl
 
@@ -31,20 +31,26 @@ def vllm_version_matches_substr(substr: str) -> bool:
 
 
 def tpu_platform_plugin() -> Optional[str]:
-    is_tpu = False
     logger.debug("Checking if TPU platform is available.")
+
+    # Check for Pathways TPU proxy
+    if envs.VLLM_TPU_USING_PATHWAYS:
+        logger.debug("Confirmed TPU platform is available via Pathways proxy.")
+        return "tpu_commons.platforms.tpu_jax.TpuPlatform"
+
+    # Check for libtpu installation
     try:
         # While it's technically possible to install libtpu on a
         # non-TPU machine, this is a very uncommon scenario. Therefore,
-        # we assume that libtpu is installed if and only if the machine
+        # we assume that libtpu is installed only if the machine
         # has TPUs.
+
         import libtpu  # noqa: F401
-        is_tpu = True
         logger.debug("Confirmed TPU platform is available.")
+        return "vllm.platforms.tpu.TpuPlatform"
     except Exception as e:
         logger.debug("TPU platform is not available because: %s", str(e))
-
-    return "vllm.platforms.tpu.TpuPlatform" if is_tpu else None
+        return None
 
 
 def cuda_platform_plugin() -> Optional[str]: