drm/i915: Zero out SAGV wm when we don't have enough DDB for it

Let's handle the SAGV WM0 more like the other wm levels and just
totally zero it out when we don't have the DDB space to back it
up.

Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210226153204.1270-3-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>

drivers/gpu/drm/i915/intel_pm.c

@@ -3921,12 +3921,10 @@ static bool tgl_crtc_can_enable_sagv(const struct intel_crtc_state *crtc_state)
 		return true;
 
 	for_each_plane_id_on_crtc(crtc, plane_id) {
-		const struct skl_ddb_entry *plane_alloc =
-			&crtc_state->wm.skl.plane_ddb_y[plane_id];
 		const struct skl_plane_wm *wm =
 			&crtc_state->wm.skl.optimal.planes[plane_id];
 
-		if (skl_ddb_entry_size(plane_alloc) < wm->sagv_wm0.min_ddb_alloc)
+		if (wm->wm[0].plane_en && !wm->sagv_wm0.plane_en)
 			return false;
 	}
 
@@ -4957,15 +4955,18 @@ skl_allocate_plane_ddb(struct intel_atomic_state *state,
 	}
 
 	/*
-	 * Go back and disable the transition watermark if it turns out we
-	 * don't have enough DDB blocks for it.
+	 * Go back and disable the transition and SAGV watermarks
+	 * if it turns out we don't have enough DDB blocks for them.
 	 */
 	for_each_plane_id_on_crtc(crtc, plane_id) {
 		struct skl_plane_wm *wm =
 			&crtc_state->wm.skl.optimal.planes[plane_id];
 
 		if (wm->trans_wm.plane_res_b >= total[plane_id])
 			memset(&wm->trans_wm, 0, sizeof(wm->trans_wm));
+
+		if (wm->sagv_wm0.plane_res_b >= total[plane_id])
+			memset(&wm->sagv_wm0, 0, sizeof(wm->sagv_wm0));
 	}
 
 	return 0;