drm/msm: use devm_gpiod_get_optional for optional reset gpio

Since 39b2bbe3d715 (gpio: add flags argument to gpiod_get*() functions)
which appeared in v3.17-rc1, the gpiod_get* functions take an additional
parameter that allows to specify direction and initial value for output.

Also there is a variant to find optional gpios that returns NULL if
there is no gpio instead of -ENOENT.

Make use of both features to simplify the driver.

This makes error checking more strict because errors like -ENOSYS ("no
gpio support compiled in") or -EPROBE_DEFER ("gpio not ready yet") are
handled correctly now.

Furthermore this is one caller less that stops us making the flags
argument to gpiod_get*() mandatory.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/dsi/dsi_host.c

@@ -1349,36 +1349,19 @@ static irqreturn_t dsi_host_irq(int irq, void *ptr)
 static int dsi_host_init_panel_gpios(struct msm_dsi_host *msm_host,
 			struct device *panel_device)
 {
-	int ret;
-
-	msm_host->disp_en_gpio = devm_gpiod_get(panel_device,
-						"disp-enable");
+	msm_host->disp_en_gpio = devm_gpiod_get_optional(panel_device,
+							 "disp-enable",
+							 GPIOD_OUT_LOW);
 	if (IS_ERR(msm_host->disp_en_gpio)) {
 		DBG("cannot get disp-enable-gpios %ld",
 				PTR_ERR(msm_host->disp_en_gpio));
-		msm_host->disp_en_gpio = NULL;
-	}
-	if (msm_host->disp_en_gpio) {
-		ret = gpiod_direction_output(msm_host->disp_en_gpio, 0);
-		if (ret) {
-			pr_err("cannot set dir to disp-en-gpios %d\n", ret);
-			return ret;
-		}
+		return PTR_ERR(msm_host->disp_en_gpio);
 	}
 
-	msm_host->te_gpio = devm_gpiod_get(panel_device, "disp-te");
+	msm_host->te_gpio = devm_gpiod_get(panel_device, "disp-te", GPIOD_IN);
 	if (IS_ERR(msm_host->te_gpio)) {
 		DBG("cannot get disp-te-gpios %ld", PTR_ERR(msm_host->te_gpio));
-		msm_host->te_gpio = NULL;
-	}
-
-	if (msm_host->te_gpio) {
-		ret = gpiod_direction_input(msm_host->te_gpio);
-		if (ret) {
-			pr_err("%s: cannot set dir to disp-te-gpios, %d\n",
-				__func__, ret);
-			return ret;
-		}
+		return PTR_ERR(msm_host->te_gpio);
 	}
 
 	return 0;