[PATCH] drm/i915/display: Allow async flips on planes with no framebuffer changes

[Naveen Kumar <naveen1.kumar@intel.com>]

Allow asynchronous page flips on planes that either lack a framebuffer or
retain the same framebuffer, as long as no plane properties are modified.

This avoids unnecessary failures in async flip paths when the update is
effectively a no-op, improving compatibility with some compositors.

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13834
Signed-off-by: Naveen Kumar <naveen1.kumar@intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 18 +++++++++------
 drivers/gpu/drm/i915/display/intel_plane.c   | 24 ++++++++++++++++++++
 2 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index 456fc4b04cda..e0eb0de62ff4 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -5970,18 +5970,21 @@ static int intel_async_flip_check_uapi(struct intel_atomic_state *state,
 		 * this(vlv/chv and icl+) should be added when async flip is
 		 * enabled in the atomic IOCTL path.
 		 */
-		if (!plane->async_flip) {
+		if (!plane->async_flip && new_plane_state->uapi.fb) {
 			drm_dbg_kms(display->drm,
 				    "[PLANE:%d:%s] async flip not supported\n",
 				    plane->base.base.id, plane->base.name);
 			return -EINVAL;
 		}
 
-		if (!old_plane_state->uapi.fb || !new_plane_state->uapi.fb) {
-			drm_dbg_kms(display->drm,
-				    "[PLANE:%d:%s] no old or new framebuffer\n",
-				    plane->base.base.id, plane->base.name);
-			return -EINVAL;
+		if (plane->base.type != DRM_PLANE_TYPE_CURSOR &&
+		    plane->base.type != DRM_PLANE_TYPE_OVERLAY) {
+			if (!old_plane_state->uapi.fb || !new_plane_state->uapi.fb) {
+				drm_dbg_kms(display->drm,
+					    "[PLANE:%d:%s] no old or new framebuffer\n",
+					    plane->base.base.id, plane->base.name);
+				return -EINVAL;
+			}
 		}
 	}
 
@@ -6034,7 +6037,8 @@ static int intel_async_flip_check_hw(struct intel_atomic_state *state, struct in
 		 * an async flip. We should never get this far otherwise.
 		 */
 		if (drm_WARN_ON(display->drm,
-				new_crtc_state->do_async_flip && !plane->async_flip))
+				new_crtc_state->do_async_flip && !plane->async_flip &&
+				new_plane_state->hw.fb))
 			return -EINVAL;
 
 		/*
diff --git a/drivers/gpu/drm/i915/display/intel_plane.c b/drivers/gpu/drm/i915/display/intel_plane.c
index 36fb07471deb..434be91b57df 100644
--- a/drivers/gpu/drm/i915/display/intel_plane.c
+++ b/drivers/gpu/drm/i915/display/intel_plane.c
@@ -1425,9 +1425,33 @@ static int intel_get_scanout_buffer(struct drm_plane *plane,
 	return 0;
 }
 
+static int
+intel_plane_atomic_async_check(struct drm_plane *plane,
+			       struct drm_atomic_state *_state, bool flip)
+{
+	struct intel_atomic_state *state = to_intel_atomic_state(_state);
+	struct intel_plane *intel_plane;
+	const struct intel_plane_state *old_plane_state;
+	struct intel_plane_state *new_plane_state;
+	int i;
+
+	for_each_oldnew_intel_plane_in_state(state, intel_plane, old_plane_state,
+					     new_plane_state, i) {
+		if (intel_plane->id != to_intel_plane(plane)->id)
+			continue;
+
+		/* no old or new framebuffer */
+		if (flip && !old_plane_state->uapi.fb && !new_plane_state->uapi.fb)
+			return 0;
+	}
+
+	return -EINVAL;
+}
+
 static const struct drm_plane_helper_funcs intel_plane_helper_funcs = {
 	.prepare_fb = intel_prepare_plane_fb,
 	.cleanup_fb = intel_cleanup_plane_fb,
+	.atomic_async_check = intel_plane_atomic_async_check,
 };
 
 static const struct drm_plane_helper_funcs intel_primary_plane_helper_funcs = {
-- 
2.48.1