[BugFix][DSv32] Fix DSA-CP PD role gating for deepseek v3.2 (v0.18.0) (#8291)

### What this PR does / why we need it?
This PR backports the DSA-CP PD role gating fix to `releases/v0.18.0`.

The existing helper logic on the release branch does not handle the PD
mixed-role case correctly when deciding whether layer sharding or TP
`o_proj` handling should be enabled. Layer sharding should only run on
the P-side instance, while TP `o_proj` handling should stay enabled for
normal non-PD deployments and for the PD mixed-role (`kv_both`)
instance. This patch makes those conditions explicit and adds unit
coverage for the allowed and disallowed combinations, including the
DSA-CP-disabled path.

Such wrong condition lead to **vllm serve failures** in case: **FC1 +
PD-colocated KV pooling + no layer_sharding**, specifically causing:
1. insufficient Available KV cache memory
2. o_proj shape error in sfa_v1 attention module

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
E2E test with dsv32 + FC1 + FULL_DECODE_ONLY +
kv_transfer_config(kv_both) + no layer_sharding

---------

Signed-off-by: chenchuw886 <chenchuw@huawei.com>
Co-authored-by: chenchuw886 <chenchuw@huawei.com>

tests/ut/test_utils.py

@@ -36,6 +36,7 @@ class TestUtils(TestBase):
         from vllm_ascend import platform
         importlib.reload(platform)
         utils.enable_dsa_cp_with_layer_shard.cache_clear()
+        utils.enable_dsa_cp_with_o_proj_tp.cache_clear()
 
     def test_nd_to_nz_2d(self):
         # can be divided by 16
@@ -134,7 +135,9 @@ class TestUtils(TestBase):
 
     def test_enable_dsa_cp_with_layer_shard_accepts_kv_producer(self):
         mock_vllm_config = mock.MagicMock()
-        mock_vllm_config.kv_transfer_config = mock.MagicMock(kv_role="kv_producer")
+        mock_vllm_config.kv_transfer_config = mock.MagicMock(
+            kv_role="kv_producer", is_kv_producer=True, is_kv_consumer=False
+        )
 
         with mock.patch("vllm.config.get_current_vllm_config", return_value=mock_vllm_config), \
              mock.patch("vllm_ascend.utils.enable_dsa_cp", return_value=True):
@@ -142,7 +145,9 @@ class TestUtils(TestBase):
 
     def test_enable_dsa_cp_with_layer_shard_rejects_kv_both(self):
         mock_vllm_config = mock.MagicMock()
-        mock_vllm_config.kv_transfer_config = mock.MagicMock(kv_role="kv_both", is_kv_producer=True)
+        mock_vllm_config.kv_transfer_config = mock.MagicMock(
+            kv_role="kv_both", is_kv_producer=True, is_kv_consumer=True
+        )
 
         with mock.patch("vllm.config.get_current_vllm_config", return_value=mock_vllm_config), \
              mock.patch("vllm_ascend.utils.enable_dsa_cp", return_value=True):
@@ -156,6 +161,42 @@ class TestUtils(TestBase):
              mock.patch("vllm_ascend.utils.enable_dsa_cp", return_value=True):
             self.assertFalse(utils.enable_dsa_cp_with_layer_shard())
 
+    def test_enable_dsa_cp_with_layer_shard_rejects_when_dsa_cp_disabled(self):
+        with mock.patch("vllm_ascend.utils.enable_dsa_cp", return_value=False):
+            self.assertFalse(utils.enable_dsa_cp_with_layer_shard())
+
+    def test_enable_dsa_cp_with_o_proj_tp_accepts_missing_kv_transfer(self):
+        mock_vllm_config = mock.MagicMock()
+        mock_vllm_config.kv_transfer_config = None
+
+        with mock.patch("vllm.config.get_current_vllm_config", return_value=mock_vllm_config), \
+             mock.patch("vllm_ascend.utils.enable_dsa_cp", return_value=True):
+            self.assertTrue(utils.enable_dsa_cp_with_o_proj_tp())
+
+    def test_enable_dsa_cp_with_o_proj_tp_accepts_kv_both(self):
+        mock_vllm_config = mock.MagicMock()
+        mock_vllm_config.kv_transfer_config = mock.MagicMock(
+            kv_role="kv_both", is_kv_producer=True, is_kv_consumer=True
+        )
+
+        with mock.patch("vllm.config.get_current_vllm_config", return_value=mock_vllm_config), \
+             mock.patch("vllm_ascend.utils.enable_dsa_cp", return_value=True):
+            self.assertTrue(utils.enable_dsa_cp_with_o_proj_tp())
+
+    def test_enable_dsa_cp_with_o_proj_tp_rejects_single_role_pd(self):
+        mock_vllm_config = mock.MagicMock()
+        mock_vllm_config.kv_transfer_config = mock.MagicMock(
+            kv_role="kv_producer", is_kv_producer=True, is_kv_consumer=False
+        )
+
+        with mock.patch("vllm.config.get_current_vllm_config", return_value=mock_vllm_config), \
+             mock.patch("vllm_ascend.utils.enable_dsa_cp", return_value=True):
+            self.assertFalse(utils.enable_dsa_cp_with_o_proj_tp())
+
+    def test_enable_dsa_cp_with_o_proj_tp_rejects_when_dsa_cp_disabled(self):
+        with mock.patch("vllm_ascend.utils.enable_dsa_cp", return_value=False):
+            self.assertFalse(utils.enable_dsa_cp_with_o_proj_tp())
+
     def test_vllm_version_is(self):
         with mock.patch.dict(os.environ, {"VLLM_VERSION": "1.0.0"}):
             with mock.patch("vllm.__version__", "1.0.0"):

vllm_ascend/utils.py

@@ -1252,11 +1252,10 @@ def enable_dsa_cp_with_layer_shard() -> bool:
     from vllm.config import get_current_vllm_config
 
     vllm_config = get_current_vllm_config()
-    # because the broadcast in layer sharding needs to be overlapped with a heavy compute stream to be
+    kv_transfer_config = vllm_config.kv_transfer_config
-    # effectively hidden, it is enabled only during the prefill stage.
+    # Layer sharding broadcast only pays off when it can be hidden by the
-    is_prefill_instance = (
+    # heavier prefill-stage compute, so enable it only on the P-side instance.
-        vllm_config.kv_transfer_config is not None and vllm_config.kv_transfer_config.kv_role == "kv_producer"
+    is_prefill_instance = kv_transfer_config is not None and kv_transfer_config.kv_role == "kv_producer"
-    )
     return is_prefill_instance
 
 
@@ -1267,9 +1266,12 @@ def enable_dsa_cp_with_o_proj_tp() -> bool:
     from vllm.config import get_current_vllm_config
 
     vllm_config = get_current_vllm_config()
-    # if is PD mix stage, using original TP o_proj weight, and also need to
+    kv_transfer_config = vllm_config.kv_transfer_config
-    # full gather for o_proj weight for prefill stage.
+
-    return vllm_config.kv_transfer_config is None
+    # In PD-mixed mode, keep the original TP o_proj weight when:
+    # 1) KV pooling is disabled, or
+    # 2) KV pooling is enabled with kv_role == "kv_both".
+    return kv_transfer_config is None or kv_transfer_config.kv_role == "kv_both"
 
 
 def check_gdn_layer(vllm_config) -> bool: