drm/tidss: dispc: Fix broken plane positioning code

The old implementation of placing planes on the CRTC while configuring
the planes was naive and relied on the order in which the planes were
configured, enabled, and disabled. The situation where a plane's zpos
was changed on the fly was completely broken. The usual symptoms of
this problem was scrambled display and a flood of sync lost errors,
when a plane was active in two layers at the same time, or a missing
plane, in case when a layer was accidentally disabled.

The rewrite takes a more straight forward approach when HW is
concerned. The plane positioning registers are in the CRTC (or
actually OVR) register space and it is more natural to configure them
in a one go when configuring the CRTC. To do this we need make sure we
have all the planes on the updated CRTCs in the new atomic state. The
untouched planes on CRTCs that need plane position update are added to
the atomic state in tidss_atomic_check().

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200227120052.23168-1-jsarha@ti.com

1 files changed, 51 insertions, 1 deletions

diff --git a/drivers/gpu/drm/tidss/tidss_kms.c b/drivers/gpu/drm/tidss/tidss_kms.c
index 3b6f8d54a016..7d419960b030 100644
--- a/drivers/gpu/drm/tidss/tidss_kms.c
+++ b/drivers/gpu/drm/tidss/tidss_kms.c
@@ -47,9 +47,59 @@ static const struct drm_mode_config_helper_funcs mode_config_helper_funcs = {
 	.atomic_commit_tail = tidss_atomic_commit_tail,
 };
 
+static int tidss_atomic_check(struct drm_device *ddev,
+			      struct drm_atomic_state *state)
+{
+	struct drm_plane_state *opstate;
+	struct drm_plane_state *npstate;
+	struct drm_plane *plane;
+	struct drm_crtc_state *cstate;
+	struct drm_crtc *crtc;
+	int ret, i;
+
+	ret = drm_atomic_helper_check(ddev, state);
+	if (ret)
+		return ret;
+
+	/*
+	 * Add all active planes on a CRTC to the atomic state, if
+	 * x/y/z position or activity of any plane on that CRTC
+	 * changes. This is needed for updating the plane positions in
+	 * tidss_crtc_position_planes() which is called from
+	 * crtc_atomic_enable() and crtc_atomic_flush(). We have an
+	 * extra flag to to mark x,y-position changes and together
+	 * with zpos_changed the condition recognizes all the above
+	 * cases.
+	 */
+	for_each_oldnew_plane_in_state(state, plane, opstate, npstate, i) {
+		if (!npstate->crtc || !npstate->visible)
+			continue;
+
+		if (!opstate->crtc || opstate->crtc_x != npstate->crtc_x ||
+		    opstate->crtc_y != npstate->crtc_y) {
+			cstate = drm_atomic_get_crtc_state(state,
+							   npstate->crtc);
+			if (IS_ERR(cstate))
+				return PTR_ERR(cstate);
+			to_tidss_crtc_state(cstate)->plane_pos_changed = true;
+		}
+	}
+
+	for_each_new_crtc_in_state(state, crtc, cstate, i) {
+		if (to_tidss_crtc_state(cstate)->plane_pos_changed ||
+		    cstate->zpos_changed) {
+			ret = drm_atomic_add_affected_planes(state, crtc);
+			if (ret)
+				return ret;
+		}
+	}
+
+	return 0;
+}
+
 static const struct drm_mode_config_funcs mode_config_funcs = {
 	.fb_create = drm_gem_fb_create,
-	.atomic_check = drm_atomic_helper_check,
+	.atomic_check = tidss_atomic_check,
 	.atomic_commit = drm_atomic_helper_commit,
 };