[diffusion] [AMD] model: allow AITER backends in Flux 2 pipeline (#22802)

python/sglang/multimodal_gen/runtime/layers/attention/backends/aiter.py

@@ -71,16 +71,14 @@ class AITerImpl(AttentionImpl):
         Performs attention using aiter.flash_attn_func.
 
         Args:
-            query: Query tensor of shape [batch_size, num_heads, seq_len, head_dim]
-            key: Key tensor of shape [batch_size, num_heads, seq_len, head_dim]
-            value: Value tensor of shape [batch_size, num_heads, seq_len, head_dim]
+            query: Query tensor of shape [batch_size, seq_len, num_heads, head_dim]
+            key: Key tensor of shape [batch_size, seq_len, num_heads, head_dim]
+            value: Value tensor of shape [batch_size, seq_len, num_heads, head_dim]
             attn_metadata: Metadata for the attention operation (unused).
 
         Returns:
-            Output tensor of shape [batch_size, num_heads, seq_len, head_dim]
+            Output tensor of shape [batch_size, seq_len, num_heads, head_dim]
         """
-        # aiter.flash_attn_func expects tensors in [B, H, S, D] layout,
-        # which is what ring_attn provides.
         output, _ = aiter.flash_attn_func(
             query,
             key,

python/sglang/multimodal_gen/runtime/models/dits/flux_2.py

@@ -865,6 +865,8 @@ class Flux2Transformer2DModel(CachableDiT, OffloadableDiTMixin):
     _supported_attention_backends = {
         AttentionBackendEnum.TORCH_SDPA,
         AttentionBackendEnum.FA,
+        AttentionBackendEnum.AITER,
+        AttentionBackendEnum.AITER_SAGE,
     }
 
     def post_load_weights(self) -> None: