drm/amd/display: Don't replace a sink mode that shares the native totals

decide_crtc_timing_for_drm_display_mode() copies the native mode's CRTC
timing into the requested mode when clock, htotal and vtotal match.
That is meant for the modes amdgpu inserts itself:
amdgpu_dm_create_common_mode() duplicates the native mode and changes
only hdisplay and vdisplay, so those are sent with the native timing
and scaled.

A sink can also offer a real mode with the same clock and totals as
its native mode. CTA-861 VIC 102 (4096x2160@60) and VIC 97
(3840x2160@60) both use 594 MHz and 4400x2250. With 3840x2160@60 as
the preferred mode, a 4096x2160@60 request goes out with the 3840x2160
timing and the framebuffer scaled into it (dst 3840x2025 at y=67),
while the AVI InfoFrame still carries VIC 102. A JVC projector then
reports 3840x2160 and shows a corrupted right edge. 4096x2160@24,
whose totals differ, is sent and displayed correctly.

Inserted modes keep the native sync positions; a real mode with its
own active width does not. Compare those too, so only inserted modes
are patched.

Fixes: 4562236b3bc0 ("drm/amd/dc: Add dc display driver (v2)")
Signed-off-by: Adrian Betschart <adrian.betschart@cinemaone.ch>
Assisted-by: Claude-Code:claude-opus-5-5
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Roman Li <roman.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

2 files changed, 48 insertions, 1 deletions

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c
index b2eb6ab6b890..5a80d0012f04 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c
@@ -1013,10 +1013,15 @@ decide_crtc_timing_for_drm_display_mode(struct drm_display_mode *drm_mode,
 					const struct drm_display_mode *native_mode,
 					bool scale_enabled)
 {
+	/* Inserted modes copy the native sync; a sink mode with equal totals may not */
 	if (scale_enabled || (
 	    native_mode->clock == drm_mode->clock &&
 	    native_mode->htotal == drm_mode->htotal &&
-	    native_mode->vtotal == drm_mode->vtotal)) {
+	    native_mode->vtotal == drm_mode->vtotal &&
+	    native_mode->hsync_start == drm_mode->hsync_start &&
+	    native_mode->hsync_end == drm_mode->hsync_end &&
+	    native_mode->vsync_start == drm_mode->vsync_start &&
+	    native_mode->vsync_end == drm_mode->vsync_end)) {
 		if (native_mode->crtc_clock)
 			copy_crtc_timing_for_drm_display_mode(native_mode, drm_mode);
 	} else {
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_connector_test.c b/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_connector_test.c
index 49a636e834bd..5fdf8ce023b9 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_connector_test.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_connector_test.c
@@ -1578,6 +1578,46 @@ static void dm_test_decide_crtc_timing_no_crtc_clock(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, drm_mode.crtc_hdisplay, 0);
 }
 
+static void dm_test_decide_crtc_timing_sink_mode_same_totals(struct kunit *test)
+{
+	struct drm_display_mode native_mode = {
+		DRM_MODE("3840x2160", DRM_MODE_TYPE_DRIVER, 594000, 3840, 4016, 4104,
+			 4400, 0, 2160, 2168, 2178, 2250, 0,
+			 DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC) };
+	struct drm_display_mode drm_mode = {
+		DRM_MODE("4096x2160", DRM_MODE_TYPE_DRIVER, 594000, 4096, 4184, 4272,
+			 4400, 0, 2160, 2168, 2178, 2250, 0,
+			 DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC) };
+
+	drm_mode_set_crtcinfo(&native_mode, 0);
+	drm_mode_set_crtcinfo(&drm_mode, 0);
+
+	decide_crtc_timing_for_drm_display_mode(&drm_mode, &native_mode, false);
+
+	KUNIT_EXPECT_EQ(test, drm_mode.crtc_hdisplay, 4096);
+	KUNIT_EXPECT_EQ(test, drm_mode.crtc_hsync_start, 4184);
+}
+
+static void dm_test_decide_crtc_timing_inserted_mode(struct kunit *test)
+{
+	struct drm_display_mode native_mode = {
+		DRM_MODE("3840x2160", DRM_MODE_TYPE_DRIVER, 594000, 3840, 4016, 4104,
+			 4400, 0, 2160, 2168, 2178, 2250, 0,
+			 DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC) };
+	struct drm_display_mode drm_mode;
+
+	drm_mode_set_crtcinfo(&native_mode, 0);
+	drm_mode = native_mode;
+	drm_mode.hdisplay = 1920;
+	drm_mode.vdisplay = 1080;
+	drm_mode_set_crtcinfo(&drm_mode, 0);
+
+	decide_crtc_timing_for_drm_display_mode(&drm_mode, &native_mode, false);
+
+	KUNIT_EXPECT_EQ(test, drm_mode.crtc_hdisplay, 3840);
+	KUNIT_EXPECT_EQ(test, drm_mode.crtc_vdisplay, 2160);
+}
+
 /* Tests for amdgpu_dm_connector_funcs_reset() */
 
 static const struct drm_connector_funcs dm_test_connector_funcs = {
@@ -10032,6 +10072,8 @@ static struct kunit_case amdgpu_dm_connector_tests[] = {
 	KUNIT_CASE(dm_test_decide_crtc_timing_matching_mode),
 	KUNIT_CASE(dm_test_decide_crtc_timing_no_copy),
 	KUNIT_CASE(dm_test_decide_crtc_timing_no_crtc_clock),
+	KUNIT_CASE(dm_test_decide_crtc_timing_sink_mode_same_totals),
+	KUNIT_CASE(dm_test_decide_crtc_timing_inserted_mode),
 	/* amdgpu_dm_connector_funcs_reset */
 	KUNIT_CASE(dm_test_funcs_reset_sets_defaults),
 	KUNIT_CASE(dm_test_funcs_reset_edp_abm_level),