[PATCH 41/82] drm/amd/display: Test dm_dp_mst_detect DPCD probe and unplug

From: Alex Hung <[email protected]>

[WHAT]
Add KUnit tests for dm_dp_mst_detect() covering the DPCD revision probe
of a peer device, the fallback when both revision registers read back as
zero, the NAKed remote read that must leave the cached revision alone,
and the unplugged port whose disconnected status releases the remote sink
and resets the MST connector state.

[HOW]
The tests reuse the MST downstream connector fixture. Its empty topology
manager makes drm_dp_mst_detect_port() report a disconnected port, which
is what the unplug path needs, and the port AUX is served by the fake
DPCD store.

Assisted-by: Copilot:Claude-Opus-5
Reviewed-by: Bhawanpreet Lakha <[email protected]>
Signed-off-by: Alex Hung <[email protected]>
Signed-off-by: Ivan Lipski <[email protected]>
---
 .../tests/amdgpu_dm_mst_types_test.c          | 111 ++++++++++++++++++
 1 file changed, 111 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_mst_types_test.c b/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_mst_types_test.c
index b74f0611dfe06..6c0d5d233dcf1 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_mst_types_test.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_mst_types_test.c
@@ -1711,6 +1711,113 @@ static void dm_mst_test_get_modes_reads_remote_edid(struct kunit *test)
 	dm_mst_test_fini_child(&child);
 }
 
+/* Tests for dm_dp_mst_detect */
+
+/**
+ * dm_mst_test_detect_reads_port_dpcd_rev - Test DPCD revision probing
+ * @test: KUnit test context
+ *
+ * For a peer device with an unknown DPCD revision, dm_dp_mst_detect() must probe
+ * DP_DP13_DPCD_REV over the port AUX and cache the returned revision.
+ */
+static void dm_mst_test_detect_reads_port_dpcd_rev(struct kunit *test)
+{
+	struct dm_mst_test_child child;
+
+	dm_mst_test_init_child(test, &child);
+	child.port->pdt = DP_PEER_DEVICE_SST_SINK;
+	/* Both DP_DP13_DPCD_REV and DP_DPCD_REV alias to offset 0 in the fake. */
+	dm_mst_test_dpcd[0] = 0x13;
+
+	KUNIT_EXPECT_EQ(test, dm_dp_mst_detect(&child.aconnector->base, NULL, false),
+			(int)connector_status_disconnected);
+
+	KUNIT_EXPECT_EQ(test, (int)child.port->dpcd_rev, 0x13);
+
+	dm_mst_test_fini_child(&child);
+}
+
+/**
+ * dm_mst_test_detect_unknown_dpcd_rev - Test unreadable DPCD revision
+ * @test: KUnit test context
+ *
+ * When both DPCD revision registers read back as zero, dm_dp_mst_detect() must
+ * leave the cached revision cleared instead of reporting a bogus value.
+ */
+static void dm_mst_test_detect_unknown_dpcd_rev(struct kunit *test)
+{
+	struct dm_mst_test_child child;
+
+	dm_mst_test_init_child(test, &child);
+	child.port->pdt = DP_PEER_DEVICE_SST_SINK;
+
+	KUNIT_EXPECT_EQ(test, dm_dp_mst_detect(&child.aconnector->base, NULL, false),
+			(int)connector_status_disconnected);
+
+	KUNIT_EXPECT_EQ(test, (int)child.port->dpcd_rev, 0);
+
+	dm_mst_test_fini_child(&child);
+}
+
+/**
+ * dm_mst_test_detect_dpcd_read_error - Test unreachable port DPCD
+ * @test: KUnit test context
+ *
+ * When the remote DPCD read is NAKed, dm_dp_mst_detect() must leave the cached
+ * revision untouched instead of storing a garbage value.
+ */
+static void dm_mst_test_detect_dpcd_read_error(struct kunit *test)
+{
+	struct dm_mst_test_child child;
+
+	dm_mst_test_init_child(test, &child);
+	child.port->pdt = DP_PEER_DEVICE_SST_SINK;
+	dm_mst_test_aux_transfer_override = -EIO;
+
+	KUNIT_EXPECT_EQ(test, dm_dp_mst_detect(&child.aconnector->base, NULL, false),
+			(int)connector_status_disconnected);
+
+	KUNIT_EXPECT_EQ(test, (int)child.port->dpcd_rev, 0);
+
+	dm_mst_test_fini_child(&child);
+}
+
+/**
+ * dm_mst_test_detect_disconnect_releases_sink - Test unplug sink release
+ * @test: KUnit test context
+ *
+ * A port with no peer device must have its cached DPCD revision cleared, and the
+ * resulting disconnected status must release the remote sink and reset the MST
+ * connector state.
+ */
+static void dm_mst_test_detect_disconnect_releases_sink(struct kunit *test)
+{
+	struct dm_mst_test_child child;
+	struct dc_sink *sink;
+
+	dm_mst_test_init_child(test, &child);
+	child.port->pdt = DP_PEER_DEVICE_NONE;
+	child.port->dpcd_rev = 0x14;
+
+	sink = dm_mst_test_alloc_sink(test);
+	child.aconnector->dc_sink = sink;
+	child.aconnector->dsc_aux = &child.port->aux;
+	child.aconnector->mst_local_bw = 1234;
+	child.link->sink_count = 1;
+
+	KUNIT_EXPECT_EQ(test, dm_dp_mst_detect(&child.aconnector->base, NULL, false),
+			(int)connector_status_disconnected);
+
+	KUNIT_EXPECT_EQ(test, (int)child.port->dpcd_rev, 0);
+	KUNIT_EXPECT_EQ(test, dm_mst_test_remove_remote_sink_calls, 1U);
+	KUNIT_EXPECT_PTR_EQ(test, dm_mst_test_removed_sink, sink);
+	KUNIT_EXPECT_NULL(test, child.aconnector->dc_sink);
+	KUNIT_EXPECT_NULL(test, child.aconnector->dsc_aux);
+	KUNIT_EXPECT_EQ(test, child.aconnector->mst_local_bw, 0U);
+
+	dm_mst_test_fini_child(&child);
+}
+
 /*
  * Sideband connector with a live topology manager and the DOWN_REP ready bit
  * armed, so dm_handle_mst_sideband_msg_ready_event() reaches its ack path.
@@ -1859,6 +1966,10 @@ static struct kunit_case dm_mst_types_test_cases[] = {
 	KUNIT_CASE(dm_mst_test_atomic_check_no_old_crtc),
 	/* dm_dp_mst_detect tests */
 	KUNIT_CASE(dm_mst_test_detect_unregistered),
+	KUNIT_CASE(dm_mst_test_detect_reads_port_dpcd_rev),
+	KUNIT_CASE(dm_mst_test_detect_unknown_dpcd_rev),
+	KUNIT_CASE(dm_mst_test_detect_dpcd_read_error),
+	KUNIT_CASE(dm_mst_test_detect_disconnect_releases_sink),
 	/* dm_dp_mst_get_modes tests */
 	KUNIT_CASE(dm_mst_test_get_modes_no_edid_adds_default_sink),
 	KUNIT_CASE(dm_mst_test_get_modes_no_edid_sink_alloc_fails),
-- 
2.43.0