[PATCH 1/2] drm: Fix dirtyfb stalls

[Rob Clark]

From: Rob Clark <robdclark at chromium.org>

drm_atomic_helper_dirtyfb() will end up stalling for vblank on "video
mode" type displays, which is pointless and unnecessary.  Add an
optional helper vfunc to determine if a plane is attached to a CRTC
that actually needs dirtyfb, and skip over them.

Signed-off-by: Rob Clark <robdclark at chromium.org>
---
 drivers/gpu/drm/drm_damage_helper.c      |  8 ++++++++
 include/drm/drm_modeset_helper_vtables.h | 14 ++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/drm_damage_helper.c b/drivers/gpu/drm/drm_damage_helper.c
index 3a4126dc2520..a0bed1a2c2dc 100644
--- a/drivers/gpu/drm/drm_damage_helper.c
+++ b/drivers/gpu/drm/drm_damage_helper.c
@@ -211,6 +211,7 @@ int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
 retry:
 	drm_for_each_plane(plane, fb->dev) {
 		struct drm_plane_state *plane_state;
+		struct drm_crtc *crtc;
 
 		ret = drm_modeset_lock(&plane->mutex, state->acquire_ctx);
 		if (ret)
@@ -221,6 +222,13 @@ int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
 			continue;
 		}
 
+		crtc = plane->state->crtc;
+		if (crtc->helper_private->needs_dirtyfb &&
+				!crtc->helper_private->needs_dirtyfb(crtc)) {
+			drm_modeset_unlock(&plane->mutex);
+			continue;
+		}
+
 		plane_state = drm_atomic_get_plane_state(state, plane);
 		if (IS_ERR(plane_state)) {
 			ret = PTR_ERR(plane_state);
diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index eb706342861d..afa8ec5754e7 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -487,6 +487,20 @@ struct drm_crtc_helper_funcs {
 				     bool in_vblank_irq, int *vpos, int *hpos,
 				     ktime_t *stime, ktime_t *etime,
 				     const struct drm_display_mode *mode);
+
+	/**
+	 * @needs_dirtyfb
+	 *
+	 * Optional callback used by damage helpers to determine if fb_damage_clips
+	 * update is needed.
+	 *
+	 * Returns:
+	 *
+	 * True if fb_damage_clips update is needed to handle DIRTYFB, False
+	 * otherwise.  If this callback is not implemented, then True is
+	 * assumed.
+	 */
+	bool (*needs_dirtyfb)(struct drm_crtc *crtc);
 };
 
 /**
-- 
2.30.2