mtd: rawnand: ams-delta: Make read pulses optional

Allow platforms to omit NRE pin from device configuration by requesting
that pin as optional.  In that case, also don't apply read pulse width
from chip SDR timings.  There should be no need for further code
adjustments as gpiolib can handle NULL GPIO descriptor pointers.
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200212003929.6682-9-jmkrzyszt@gmail.com

drivers/mtd/nand/raw/ams-delta.c

@@ -202,8 +202,10 @@ static int ams_delta_setup_data_interface(struct nand_chip *this, int csline,
 	if (csline == NAND_DATA_IFACE_CHECK_ONLY)
 		return 0;
 
-	priv->tRP = DIV_ROUND_UP(sdr->tRP_min, 1000);
-	dev_dbg(dev, "using %u ns read pulse width\n", priv->tRP);
+	if (priv->gpiod_nre) {
+		priv->tRP = DIV_ROUND_UP(sdr->tRP_min, 1000);
+		dev_dbg(dev, "using %u ns read pulse width\n", priv->tRP);
+	}
 
 	priv->tWP = DIV_ROUND_UP(sdr->tWP_min, 1000);
 	dev_dbg(dev, "using %u ns write pulse width\n", priv->tWP);
@@ -276,7 +278,8 @@ static int ams_delta_init(struct platform_device *pdev)
 		return err;
 	}
 
-	priv->gpiod_nre = devm_gpiod_get(&pdev->dev, "nre", GPIOD_OUT_LOW);
+	priv->gpiod_nre = devm_gpiod_get_optional(&pdev->dev, "nre",
+						  GPIOD_OUT_LOW);
 	if (IS_ERR(priv->gpiod_nre)) {
 		err = PTR_ERR(priv->gpiod_nre);
 		dev_err(&pdev->dev, "NRE GPIO request failed (%d)\n", err);