drm/i915/vrr: Fix "window2" handling

The "window2" delay is just the difference of vactive
(undelayed vblank) vs. vblank_start (delayed vblank).
Just use vblank_start during the VRR calculations so
that things work correctly regardless of whether delayed
vblank is used or not.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230127173044.24108-2-ville.syrjala@linux.intel.comReviewed-by: Jouni Högander <jouni.hogander@intel.com>

drivers/gpu/drm/i915/display/intel_vrr.c

@@ -144,17 +144,11 @@ intel_vrr_compute_config(struct intel_crtc_state *crtc_state,
 	 * is deprecated.
 	 */
 	if (DISPLAY_VER(i915) >= 13) {
-		/*
-		 * FIXME: Subtract Window2 delay from below value.
-		 *
-		 * Window2 specifies time required to program DSB (Window2) in
-		 * number of scan lines. Assuming 0 for no DSB.
-		 */
 		crtc_state->vrr.guardband =
-			crtc_state->vrr.vmin + 1 - adjusted_mode->crtc_vdisplay;
+			crtc_state->vrr.vmin + 1 - adjusted_mode->crtc_vblank_start;
 	} else {
 		crtc_state->vrr.pipeline_full =
-			min(255, crtc_state->vrr.vmin - adjusted_mode->crtc_vdisplay -
+			min(255, crtc_state->vrr.vmin - adjusted_mode->crtc_vblank_start -
 			    crtc_state->framestart_delay - 1);
 	}