lib/igt_kms: Set pipe->plane_primary to driver-assigned primary plane when there are multiple possible primary planes

Currently, IGT populates pipe->planes using possible_crtcs and assumes
that the first primary plane it encounters is the one being actively
used by the pipe.

This is not always true in cases where there are multiple possible
primary planes. This will cause problems whenever IGT calls
drmModePageFlip since drmModePageFlip will use the primary plane
assigned to the pipe by the driver to perform the page flip [1]. So a
mismatch between the primary plane used by IGT and the driver can cause
the page flip to fail.

To fix this, let's implement a helper method to get the primary plane
that's being assigned to the pipe by the driver. We can then call it
during igt_display_require() and, if there's a mismatch between
pipe->plane_primary and the assigned primary plane's index, we can swap
the unused primary plane with the driver-assigned primary plane

[1]
https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/drm_plane.c#L1234

Changes since v1:
- Instead of swapping the pointers of the planes within the array, we
  can just change the value of pipe->plane_primary.

Changes since v2:
- Reverted `if (type == DRM_PLANE_TYPE_PRIMARY)` conditional then added
  a nested if statement to increment num_primary_planes if plane type is
  primary.

Changes since v3:
- Created helper method igt_pipe_has_valid_output and added a check for
  if pipe has valid output before getting the output of a pipe to get
  the assigned primary plane
- Reverted back to using igt_swap to swap the order of the primary
  planes within the pipe->planes array. Some kms_* tests use
  igt_output_get_plane(output, 0) to get the primary plane, so this will
  avoid regressions in those tests.
- Updated the plane->index of the primary planes that are being swapped.

Suggested-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Acked-by: Petri Latvala <petri.latvala@intel.com>
Reviewed-by: Mark Yacoub <markyacoub@chromium.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/igt_kms.h b/lib/igt_kms.h
index 1f33e4f1..ba0bf4d6 100644
--- a/lib/igt_kms.h
+++ b/lib/igt_kms.h
@@ -383,6 +383,7 @@ struct igt_pipe {
 	bool enabled;
 
 	int n_planes;
+	int num_primary_planes;
 	int plane_cursor;
 	int plane_primary;
 	igt_plane_t *planes;