backend/drm: add support for FB_DAMAGE_CLIPS

This allows the kernel to access our buffer damage. Some drivers
can take advantage of this, e.g. for PSR2 panels (Panel Self
Refresh) or for transfer over USB.

Closes: https://github.com/swaywm/wlroots/issues/1267

backend/drm/atomic.c

@@ -201,6 +201,18 @@ static bool atomic_crtc_commit(struct wlr_drm_connector *conn,
 		}
 	}
 
+	uint32_t fb_damage_clips = 0;
+	if ((state->committed & WLR_OUTPUT_STATE_DAMAGE) &&
+			crtc->primary->props.fb_damage_clips != 0) {
+		int rects_len;
+		const pixman_box32_t *rects = pixman_region32_rectangles(
+			(pixman_region32_t *)&state->damage, &rects_len);
+		if (drmModeCreatePropertyBlob(drm->fd, rects,
+				sizeof(*rects) * rects_len, &fb_damage_clips) != 0) {
+			wlr_log_errno(WLR_ERROR, "Failed to create FB_DAMAGE_CLIPS property blob");
+		}
+	}
+
 	bool prev_vrr_enabled =
 		output->adaptive_sync_status == WLR_OUTPUT_ADAPTIVE_SYNC_ENABLED;
 	bool vrr_enabled = prev_vrr_enabled;
@@ -235,6 +247,10 @@ static bool atomic_crtc_commit(struct wlr_drm_connector *conn,
 			atomic_add(&atom, crtc->id, crtc->props.vrr_enabled, vrr_enabled);
 		}
 		set_plane_props(&atom, drm, crtc->primary, crtc->id, 0, 0);
+		if (crtc->primary->props.fb_damage_clips != 0) {
+			atomic_add(&atom, crtc->primary->id,
+				crtc->primary->props.fb_damage_clips, fb_damage_clips);
+		}
 		if (crtc->cursor) {
 			if (drm_connector_is_cursor_visible(conn)) {
 				set_plane_props(&atom, drm, crtc->cursor, crtc->id,
@@ -269,6 +285,11 @@ static bool atomic_crtc_commit(struct wlr_drm_connector *conn,
 		rollback_blob(drm, &crtc->gamma_lut, gamma_lut);
 	}
 
+	if (fb_damage_clips != 0 &&
+			drmModeDestroyPropertyBlob(drm->fd, fb_damage_clips) != 0) {
+		wlr_log_errno(WLR_ERROR, "Failed to destroy FB_DAMAGE_CLIPS property blob");
+	}
+
 	return ok;
 }
 

backend/drm/properties.c

@@ -47,6 +47,7 @@ static const struct prop_info plane_info[] = {
 	{ "CRTC_W", INDEX(crtc_w) },
 	{ "CRTC_X", INDEX(crtc_x) },
 	{ "CRTC_Y", INDEX(crtc_y) },
+	{ "FB_DAMAGE_CLIPS", INDEX(fb_damage_clips) },
 	{ "FB_ID", INDEX(fb_id) },
 	{ "IN_FORMATS", INDEX(in_formats) },
 	{ "SRC_H", INDEX(src_h) },

include/backend/drm/properties.h

@@ -59,8 +59,9 @@ union wlr_drm_plane_props {
 		uint32_t crtc_h;
 		uint32_t fb_id;
 		uint32_t crtc_id;
+		uint32_t fb_damage_clips;
 	};
-	uint32_t props[13];
+	uint32_t props[14];
 };
 
 bool get_drm_connector_props(int fd, uint32_t id,