drm/i915: Calculate g4x intermediate watermarks correctly

The watermarks it should calculate against are the old optimal watermarks.
The currently active crtc watermarks are pure fiction, and are invalid in
case of a nonblocking modeset, page flip enabling/disabling planes or any
other reason.

When the crtc is disabled or during a modeset the intermediate watermarks
don't need to be programmed separately, and could be directly assigned
to the optimal watermarks.

CXSR must always be disabled in the intermediate case for modesets,
else we get a WARN for vblank wait timeout.

Also rename crtc_state to new_crtc_state, to distinguish it from the old
state.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171115163157.14372-2-maarten.lankhorst@linux.intel.com
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/intel_pm.c

@@ -1406,17 +1406,29 @@ static int g4x_compute_pipe_wm(struct intel_crtc_state *crtc_state)
 
 static int g4x_compute_intermediate_wm(struct drm_device *dev,
 				       struct intel_crtc *crtc,
-				       struct intel_crtc_state *crtc_state)
+				       struct intel_crtc_state *new_crtc_state)
 {
-	struct g4x_wm_state *intermediate = &crtc_state->wm.g4x.intermediate;
-	const struct g4x_wm_state *optimal = &crtc_state->wm.g4x.optimal;
-	const struct g4x_wm_state *active = &crtc->wm.active.g4x;
+	struct g4x_wm_state *intermediate = &new_crtc_state->wm.g4x.intermediate;
+	const struct g4x_wm_state *optimal = &new_crtc_state->wm.g4x.optimal;
+	struct intel_atomic_state *intel_state =
+		to_intel_atomic_state(new_crtc_state->base.state);
+	const struct intel_crtc_state *old_crtc_state =
+		intel_atomic_get_old_crtc_state(intel_state, crtc);
+	const struct g4x_wm_state *active = &old_crtc_state->wm.g4x.optimal;
 	enum plane_id plane_id;
 
+	if (!new_crtc_state->base.active || drm_atomic_crtc_needs_modeset(&new_crtc_state->base)) {
+		*intermediate = *optimal;
+
+		intermediate->cxsr = false;
+		intermediate->hpll_en = false;
+		goto out;
+	}
+
 	intermediate->cxsr = optimal->cxsr && active->cxsr &&
-		!crtc_state->disable_cxsr;
+		!new_crtc_state->disable_cxsr;
 	intermediate->hpll_en = optimal->hpll_en && active->hpll_en &&
-		!crtc_state->disable_cxsr;
+		!new_crtc_state->disable_cxsr;
 	intermediate->fbc_en = optimal->fbc_en && active->fbc_en;
 
 	for_each_plane_id_on_crtc(crtc, plane_id) {
@@ -1458,12 +1470,13 @@ static int g4x_compute_intermediate_wm(struct drm_device *dev,
 	WARN_ON(intermediate->hpll.fbc > g4x_fbc_fifo_size(2) &&
 		intermediate->fbc_en && intermediate->hpll_en);
 
+out:
 	/*
 	 * If our intermediate WM are identical to the final WM, then we can
 	 * omit the post-vblank programming; only update if it's different.
 	 */
 	if (memcmp(intermediate, optimal, sizeof(*intermediate)) != 0)
-		crtc_state->wm.need_postvbl_update = true;
+		new_crtc_state->wm.need_postvbl_update = true;
 
 	return 0;
 }