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fix npu compatibility #13465

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fc7c419
fix npu compatibility
HsiaWinter Apr 14, 2026
51c7ea7
fix npu compatibility
HsiaWinter Apr 14, 2026
18dcd90
Merge branch 'main' into add_npu_compatibility
yiyixuxu Apr 14, 2026
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10 changes: 8 additions & 2 deletions src/diffusers/models/transformers/transformer_ernie_image.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -127,8 +127,14 @@ def apply_rotary_emb(x_in: torch.Tensor, freqs_cis: torch.Tensor) -> torch.Tenso
query, key = query.to(dtype), key.to(dtype)

# From [batch, seq_len] to [batch, 1, 1, seq_len] -> broadcast to [batch, heads, seq_len, seq_len]
if attention_mask is not None and attention_mask.ndim == 2:
attention_mask = attention_mask[:, None, None, :]
if attention_mask is not None:
if attention_mask.ndim == 2:
attention_mask = attention_mask[:, None, None, :]

if attention_mask.ndim == 4:
# NPU does not support automatic broadcasting for this type; the mask must be expanded.
if attention_mask.device.type == 'npu' and attention_mask.shape[1:3] == (1, 1):

@yiyixuxuyiyixuxuApr 14, 2026•
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can we verify if we explicitly seet the backend to npu, this would also work?

diffusers/src/diffusers/models/attention_dispatch.py

Line 3173 in 6a339ce

def_native_npu_attention(

@chang-zhijiechang-zhijieApr 14, 2026

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When a mask of shape [batch, seq_len] or [batch, 1, 1, seq_len] is passed, the operator fails with an error similar to:
get unsupported atten_mask shape, the shape is [B, 1, 1, S] – while only shapes like [B, N, S, S], [B, 1, S, S], [1, 1, S, S], or [S, S] are accepted.

The _native_npu_attention function operates correctly as it leverages _maybe_modify_attn_mask_npu to reshape the attention mask from [batch_size, seq_len_k] to [batch_size, 1, seq_len_q, seq_len_k]. This reshaped format is compatible with the NPU backend.

Reference:
Ascend NPU fusion attention API:
https://www.hiascend.com/document/detail/zh/Pytorch/730/apiref/torchnpuCustomsapi/docs/context/torch_npu-npu_fusion_attention.md

@yiyixuxuyiyixuxuApr 14, 2026

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When a mask of shape [batch, seq_len] or [batch, 1, 1, seq_len] is passed, the operator fails with an error

just want to make sure we're on the same page, could you share a code example that would produce this error on npu? specifically, I;d like to know if you are running the default attention backend, i.e. without wrapping your model call inside with attention_backend("_naive_npu")

@chang-zhijiechang-zhijieApr 15, 2026•
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Yes, this code fixes the issue with the "native" backend. After the fix, it runs correctly with the "_native_attention" backend. Here's an example:

python
import torch
import torch_npu
from diffusers import ErnieImagePipeline
from diffusers.utils import load_image
pipe = ErnieImagePipeline.from_pretrained("/model_dir/ERNIE-Image", torch_dtype=torch.bfloat16)
pipe = pipe.to("npu")
generator = torch.Generator(device="npu")
prompt = "A black and white Chinese rural dog"
images = pipe(
prompt=prompt,
height=1024,
width=1024,
num_inference_steps=50,
guidance_scale=5.0,
generator=generator,
use_pe=True,
).images
images[0].save("ernie-image-output.png")

However, I've found that when using native_npu_attention as the backend, there are still some issues with mask handling. I've pushed an additional commit to the previous PR. PR link: #13451 .
Add the following code to the example to enable the _native_npu_attention backend: pipe.transformer.set_attention_backend("_native_npu")
Note: When processing masks, we need to perform expansion validation when 4D masks are passed in, and apply mask inversion to meet the NPU interface requirements.

attention_mask = attention_mask.expand(-1, attn.heads, query.shape[1], -1)

# Compute joint attention
hidden_states = dispatch_attention_fn(
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