mtd: nand: gpio: make nCE GPIO optional

On some hardware, the nCE signal is wired to the ChipSelect associated
to bus address of the NAND, so it is automatically driven during the
memory access and it is not managed by a GPIO.
Signed-off-by: NChristophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: NMarek Vasut <marek.vasut@gmail.com>
Signed-off-by: NBoris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/nand/gpio.c

@@ -78,7 +78,9 @@ static void gpio_nand_cmd_ctrl(struct mtd_info *mtd, int cmd, unsigned int ctrl)
 	gpio_nand_dosync(gpiomtd);
 
 	if (ctrl & NAND_CTRL_CHANGE) {
-		gpio_set_value(gpiomtd->plat.gpio_nce, !(ctrl & NAND_NCE));
+		if (gpio_is_valid(gpiomtd->plat.gpio_nce))
+			gpio_set_value(gpiomtd->plat.gpio_nce,
+				       !(ctrl & NAND_NCE));
 		gpio_set_value(gpiomtd->plat.gpio_cle, !!(ctrl & NAND_CLE));
 		gpio_set_value(gpiomtd->plat.gpio_ale, !!(ctrl & NAND_ALE));
 		gpio_nand_dosync(gpiomtd);
@@ -201,7 +203,8 @@ static int gpio_nand_remove(struct platform_device *pdev)
 
 	if (gpio_is_valid(gpiomtd->plat.gpio_nwp))
 		gpio_set_value(gpiomtd->plat.gpio_nwp, 0);
-	gpio_set_value(gpiomtd->plat.gpio_nce, 1);
+	if (gpio_is_valid(gpiomtd->plat.gpio_nce))
+		gpio_set_value(gpiomtd->plat.gpio_nce, 1);
 
 	return 0;
 }
@@ -239,10 +242,13 @@ static int gpio_nand_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	ret = devm_gpio_request(&pdev->dev, gpiomtd->plat.gpio_nce, "NAND NCE");
-	if (ret)
-		return ret;
-	gpio_direction_output(gpiomtd->plat.gpio_nce, 1);
+	if (gpio_is_valid(gpiomtd->plat.gpio_nce)) {
+		ret = devm_gpio_request(&pdev->dev, gpiomtd->plat.gpio_nce,
+					"NAND NCE");
+		if (ret)
+			return ret;
+		gpio_direction_output(gpiomtd->plat.gpio_nce, 1);
+	}
 
 	if (gpio_is_valid(gpiomtd->plat.gpio_nwp)) {
 		ret = devm_gpio_request(&pdev->dev, gpiomtd->plat.gpio_nwp,