add recommendations for NPU using flash_attn (#36383)

* add recommendations for Ascend NPU using flash_attn

* update recommend_message_npu

Co-authored-by: Marc Sun <57196510+SunMarc@users.noreply.github.com>

---------

Co-authored-by: Marc Sun <57196510+SunMarc@users.noreply.github.com>

src/transformers/modeling_utils.py

@@ -97,6 +97,7 @@ from .utils import (
     is_safetensors_available,
     is_torch_flex_attn_available,
     is_torch_greater_or_equal,
+    is_torch_npu_available,
     is_torch_sdpa_available,
     is_torch_xla_available,
     logging,
@@ -1746,7 +1747,13 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin, GenerationMixin, PushToHubMix
             install_message = "Please refer to the documentation of https://huggingface.co/docs/transformers/perf_infer_gpu_one#flashattention-2 to install Flash Attention 2."
 
             if importlib.util.find_spec("flash_attn") is None:
-                raise ImportError(f"{preface} the package flash_attn seems to be not installed. {install_message}")
+                if is_torch_npu_available():
+                    recommend_message_npu = "You should use attn_implementation='sdpa' instead when using NPU. "
+                    raise ImportError(
+                        f"{preface} the package flash_attn is not supported on Ascend NPU. {recommend_message_npu}"
+                    )
+                else:
+                    raise ImportError(f"{preface} the package flash_attn seems to be not installed. {install_message}")
 
             flash_attention_version = version.parse(importlib.metadata.version("flash_attn"))
             if torch.version.cuda: