[Bugfix] DeepGEMM is not enabled on B200 due to `_lazy_init()` (#21472)

Signed-off-by: Clayton Coleman <smarterclayton@gmail.com>
Co-authored-by: mgoin <mgoin64@gmail.com>

vllm/utils/deep_gemm.py

@@ -13,7 +13,8 @@ from typing import Any, Callable, NoReturn
 import torch
 
 import vllm.envs as envs
-from vllm.utils import cuda_get_device_properties, has_deep_gemm
+from vllm.platforms import current_platform
+from vllm.utils import has_deep_gemm
 
 
 @functools.cache
@@ -21,12 +22,15 @@ def is_blackwell_deep_gemm_used() -> bool:
     """Return ``True`` if vLLM is configured to use DeepGEMM on a
     Blackwell-class GPU.
     """
+    if not (envs.VLLM_USE_DEEP_GEMM and has_deep_gemm()):
+        return False
 
-    if not (envs.VLLM_USE_DEEP_GEMM and has_deep_gemm()
-            and _per_block_cast_impl is not None):
+    _lazy_init()
+    if _per_block_cast_impl is None:
         return False
 
-    return cuda_get_device_properties(0, ("major", ))[0] == 10
+    return (current_platform.is_cuda()
+            and current_platform.is_device_capability(100))
 
 
 def _missing(*_: Any, **__: Any) -> NoReturn: