drm/tegra: dpaux: Fix crash if VDD supply is absent

In order to properly make the VDD supply optional, all accesses to the
regulator need to be ignored, because the regulator core doesn't treat
NULL special.
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/dpaux.c

@@ -505,6 +505,8 @@ static int tegra_dpaux_probe(struct platform_device *pdev)
 
 			return PTR_ERR(dpaux->vdd);
 		}
+
+		dpaux->vdd = NULL;
 	}
 
 	platform_set_drvdata(pdev, dpaux);
@@ -698,12 +700,14 @@ int drm_dp_aux_attach(struct drm_dp_aux *aux, struct tegra_output *output)
 	output->connector.polled = DRM_CONNECTOR_POLL_HPD;
 	dpaux->output = output;
 
+	if (output->panel) {
+		enum drm_connector_status status;
+
+		if (dpaux->vdd) {
 			err = regulator_enable(dpaux->vdd);
 			if (err < 0)
 				return err;
-
-	if (output->panel) {
-		enum drm_connector_status status;
+		}
 
 		timeout = jiffies + msecs_to_jiffies(250);
 
@@ -732,12 +736,14 @@ int drm_dp_aux_detach(struct drm_dp_aux *aux)
 
 	disable_irq(dpaux->irq);
 
+	if (dpaux->output->panel) {
+		enum drm_connector_status status;
+
+		if (dpaux->vdd) {
 			err = regulator_disable(dpaux->vdd);
 			if (err < 0)
 				return err;
-
-	if (dpaux->output->panel) {
-		enum drm_connector_status status;
+		}
 
 		timeout = jiffies + msecs_to_jiffies(250);