drm/i915: Push clear_intel_crtc_state() onto the heap

clear_intel_crtc_state() uses the stack for saving a temporary copy of
certain bits of the inherited crtc_state before clearing the unwanted
bits. This pushes it over the stack limit for my little 32b Pineview,
so move the temporary allocation to the heap instead. As we now use a
zeroed struct, we can copy the whole extended state back to both
preserve what bits need to be preserved and zero the rest.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190205092759.16018-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_display.c

@@ -11468,44 +11468,38 @@ static bool check_digital_port_conflicts(struct drm_atomic_state *state)
 	return ret;
 }
 
-static void
+static int
 clear_intel_crtc_state(struct intel_crtc_state *crtc_state)
 {
 	struct drm_i915_private *dev_priv =
 		to_i915(crtc_state->base.crtc->dev);
-	struct intel_crtc_scaler_state scaler_state;
-	struct intel_dpll_hw_state dpll_hw_state;
-	struct intel_shared_dpll *shared_dpll;
-	struct intel_crtc_wm_state wm_state;
-	bool force_thru, ips_force_disable;
+	struct intel_crtc_state *saved_state;
+
+	saved_state = kzalloc(sizeof(*saved_state), GFP_KERNEL);
+	if (!saved_state)
+		return -ENOMEM;
 
 	/* FIXME: before the switch to atomic started, a new pipe_config was
 	 * kzalloc'd. Code that depends on any field being zero should be
 	 * fixed, so that the crtc_state can be safely duplicated. For now,
 	 * only fields that are know to not cause problems are preserved. */
 
-	scaler_state = crtc_state->scaler_state;
-	shared_dpll = crtc_state->shared_dpll;
-	dpll_hw_state = crtc_state->dpll_hw_state;
-	force_thru = crtc_state->pch_pfit.force_thru;
-	ips_force_disable = crtc_state->ips_force_disable;
+	saved_state->scaler_state = crtc_state->scaler_state;
+	saved_state->shared_dpll = crtc_state->shared_dpll;
+	saved_state->dpll_hw_state = crtc_state->dpll_hw_state;
+	saved_state->pch_pfit.force_thru = crtc_state->pch_pfit.force_thru;
+	saved_state->ips_force_disable = crtc_state->ips_force_disable;
 	if (IS_G4X(dev_priv) ||
 	    IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
-		wm_state = crtc_state->wm;
+		saved_state->wm = crtc_state->wm;
 
 	/* Keep base drm_crtc_state intact, only clear our extended struct */
 	BUILD_BUG_ON(offsetof(struct intel_crtc_state, base));
-	memset(&crtc_state->base + 1, 0,
+	memcpy(&crtc_state->base + 1, &saved_state->base + 1,
 	       sizeof(*crtc_state) - sizeof(crtc_state->base));
 
-	crtc_state->scaler_state = scaler_state;
-	crtc_state->shared_dpll = shared_dpll;
-	crtc_state->dpll_hw_state = dpll_hw_state;
-	crtc_state->pch_pfit.force_thru = force_thru;
-	crtc_state->ips_force_disable = ips_force_disable;
-	if (IS_G4X(dev_priv) ||
-	    IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
-		crtc_state->wm = wm_state;
+	kfree(saved_state);
+	return 0;
 }
 
 static int
@@ -11520,7 +11514,9 @@ intel_modeset_pipe_config(struct drm_crtc *crtc,
 	int i;
 	bool retry = true;
 
-	clear_intel_crtc_state(pipe_config);
+	ret = clear_intel_crtc_state(pipe_config);
+	if (ret)
+		return ret;
 
 	pipe_config->cpu_transcoder =
 		(enum transcoder) to_intel_crtc(crtc)->pipe;