[diffusion] multi-platform: support diffusion on amd and fix encoder loading on MI325 (#13760)

Co-authored-by: Sabre Shao <sabre.shao@amd.com>
Co-authored-by: Yusheng (Ethan) Su <yushengsu.thu@gmail.com>
Co-authored-by: Hubert Lu <Hubert.Lu@amd.com>
Co-authored-by: xsun <sunxiao04@gmail.com>

python/sglang/multimodal_gen/runtime/distributed/parallel_state.py

@@ -404,15 +404,25 @@ def initialize_model_parallel(
     global _SP
     assert _SP is None, "sequence parallel group is already initialized"
 
-    from yunchang import set_seq_parallel_pg
-    from yunchang.globals import PROCESS_GROUP
+    try:
+        from .yunchang import PROCESS_GROUP as _YC_PROCESS_GROUP
+        from .yunchang import set_seq_parallel_pg as _set_seq_parallel_pg
+    except ImportError:
+        _set_seq_parallel_pg = None
 
-    set_seq_parallel_pg(
-        sp_ulysses_degree=ulysses_degree,
-        sp_ring_degree=ring_degree,
-        rank=get_world_group().rank_in_group,
-        world_size=dit_parallel_size,
-    )
+        class _DummyProcessGroup:
+            ULYSSES_PG = torch.distributed.group.WORLD
+            RING_PG = torch.distributed.group.WORLD
+
+        PROCESS_GROUP = _DummyProcessGroup()
+    else:
+        _set_seq_parallel_pg(
+            sp_ulysses_degree=ulysses_degree,
+            sp_ring_degree=ring_degree,
+            rank=get_world_group().rank_in_group,
+            world_size=dit_parallel_size,
+        )
+        PROCESS_GROUP = _YC_PROCESS_GROUP
 
     _SP = init_parallel_group_coordinator(
         group_ranks=rank_generator.get_ranks("sp"),