drm/panel: mantix: Fix panel reset

The mantix panel needs two reset lines (RESX and TP_RSTN) deasserted to
output an image. Only deasserting RESX is not enough and the display
will stay blank. Deassert in prepare() and assert in unprepare() to keep
device held in reset when off.
Signed-off-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/ba71a8ab010d263a8058dd4f711e3bcd95877bf2.1602584953.git.agx@sigxcpu.org

drivers/gpu/drm/panel/panel-mantix-mlaf057we51.c

@@ -26,7 +26,9 @@
 struct mantix {
 	struct device *dev;
 	struct drm_panel panel;
+
 	struct gpio_desc *reset_gpio;
+	struct gpio_desc *tp_rstn_gpio;
 
 	struct regulator *avdd;
 	struct regulator *avee;
@@ -124,6 +126,10 @@ static int mantix_unprepare(struct drm_panel *panel)
 {
 	struct mantix *ctx = panel_to_mantix(panel);
 
+	gpiod_set_value_cansleep(ctx->tp_rstn_gpio, 1);
+	usleep_range(5000, 6000);
+	gpiod_set_value_cansleep(ctx->reset_gpio, 1);
+
 	regulator_disable(ctx->avee);
 	regulator_disable(ctx->avdd);
 	/* T11 */
@@ -165,13 +171,10 @@ static int mantix_prepare(struct drm_panel *panel)
 		return ret;
 	}
 
-	/* T3+T5 */
-	usleep_range(10000, 12000);
-
-	gpiod_set_value_cansleep(ctx->reset_gpio, 1);
-	usleep_range(5150, 7000);
-
+	/* T3 + T4 + time for voltage to become stable: */
+	usleep_range(6000, 7000);
 	gpiod_set_value_cansleep(ctx->reset_gpio, 0);
+	gpiod_set_value_cansleep(ctx->tp_rstn_gpio, 0);
 
 	/* T6 */
 	msleep(50);
@@ -236,12 +239,18 @@ static int mantix_probe(struct mipi_dsi_device *dsi)
 	if (!ctx)
 		return -ENOMEM;
 
-	ctx->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_LOW);
+	ctx->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
 	if (IS_ERR(ctx->reset_gpio)) {
 		dev_err(dev, "cannot get reset gpio\n");
 		return PTR_ERR(ctx->reset_gpio);
 	}
 
+	ctx->tp_rstn_gpio = devm_gpiod_get(dev, "mantix,tp-rstn", GPIOD_OUT_HIGH);
+	if (IS_ERR(ctx->tp_rstn_gpio)) {
+		dev_err(dev, "cannot get tp-rstn gpio\n");
+		return PTR_ERR(ctx->tp_rstn_gpio);
+	}
+
 	mipi_dsi_set_drvdata(dsi, ctx);
 	ctx->dev = dev;