[PATCH i-g-t] tests/kms_plane: Add vblank waits for MediaTek CRC timing

[Jason-JH Lin <jason-jh.lin@mediatek.com>]

On MediaTek hardware, CRC generation requires additional time to
stabilize after certain operations. This patch adds targeted vblank
waits for two specific scenarios:

1. Pixel format changes: After a format change in
   capture_format_crcs_single(), the CRC hardware needs at least one
   vblank to generate valid CRC values for the new format. Without
   this wait, tests may read stale or transitional CRC values.

2. Cursor plane updates: In test_plane_position_with_output(), cursor
   plane updates are non-blocking on MediaTek hardware. A vblank wait
   ensures the CRC reflects the updated plane configuration.

These waits are guarded by is_mtk_device() checks to avoid affecting
other platforms.

Fixes failures in:
- pixel-format: CRC mismatch due to reading before format stabilization
- plane-position-hole: pipe-A-plane-3 failures with cursor plane

Signed-off-by: Jason-JH Lin <jason-jh.lin@mediatek.com>
---
 tests/kms_plane.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tests/kms_plane.c b/tests/kms_plane.c
index 8cef94a1f37e..e4539078c98e 100644
--- a/tests/kms_plane.c
+++ b/tests/kms_plane.c
@@ -351,6 +351,15 @@ test_plane_position_with_output(data_t *data, igt_crtc_t *crtc,
 
 	igt_display_commit(&data->display);
 
+	/*
+	 * On MediaTek hardware, cursor plane updates are non-blocking and
+	 * CRC needs time to reflect the new plane configuration. Wait for
+	 * a vblank to ensure the update has taken effect.
+	 */
+	if (is_mtk_device(data->drm_fd) && sprite->type == DRM_PLANE_TYPE_CURSOR)
+		igt_wait_for_vblank(data->drm_fd,
+				    data->display.pipes[pipe].crtc_offset);
+
 	igt_pipe_crc_collect_crc(data->pipe_crc, &crc);
 	igt_assert_crc_equal(reference_crc, &crc);
 
@@ -760,6 +769,15 @@ static void capture_format_crcs_single(data_t *data, igt_crtc_t *crtc,
 
 	igt_remove_fb(data->drm_fd, &old_fb);
 
+	/*
+	 * On MediaTek hardware, CRC generation needs time to stabilize after
+	 * a pixel format change. Wait for at least one vblank to ensure the
+	 * CRC hardware has updated for the new format.
+	 */
+	if (is_mtk_device(data->drm_fd))
+		igt_wait_for_vblank(data->drm_fd,
+				    data->display.pipes[pipe].crtc_offset);
+
 	igt_pipe_crc_get_current(data->drm_fd, data->pipe_crc, &crc[0]);
 }
 
-- 
2.43.0