mtd: rawnand: ams-delta: Write protect device during probe

Initialise NWP GPIO pin as asserted to protect the device from hazard
during setup of other GPIO pins.
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200212003929.6682-2-jmkrzyszt@gmail.com

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

@@ -251,8 +251,8 @@ static int ams_delta_init(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, priv);
 
-	/* Set chip enabled, but  */
-	priv->gpiod_nwp = devm_gpiod_get(&pdev->dev, "nwp", GPIOD_OUT_HIGH);
+	/* Set chip enabled but write protected */
+	priv->gpiod_nwp = devm_gpiod_get(&pdev->dev, "nwp", GPIOD_OUT_LOW);
 	if (IS_ERR(priv->gpiod_nwp)) {
 		err = PTR_ERR(priv->gpiod_nwp);
 		dev_err(&pdev->dev, "NWP GPIO request failed (%d)\n", err);
@@ -309,6 +309,17 @@ static int ams_delta_init(struct platform_device *pdev)
 	nand_controller_init(&priv->base);
 	this->controller = &priv->base;
 
+	/*
+	 * FIXME: We should release write protection only after nand_scan() to
+	 * be on the safe side but we can't do that until we have a generic way
+	 * to assert/deassert WP from the core.  Even if the core shouldn't
+	 * write things in the nand_scan() path, it should have control on this
+	 * pin just in case we ever need to disable write protection during
+	 * chip detection/initialization.
+	 */
+	/* Release write protection */
+	gpiod_set_value(priv->gpiod_nwp, 1);
+
 	/* Scan to find existence of the device */
 	err = nand_scan(this, 1);
 	if (err)
@@ -336,6 +347,9 @@ static int ams_delta_cleanup(struct platform_device *pdev)
 	struct ams_delta_nand *priv = platform_get_drvdata(pdev);
 	struct mtd_info *mtd = nand_to_mtd(&priv->nand_chip);
 
+	/* Apply write protection */
+	gpiod_set_value(priv->gpiod_nwp, 0);
+
 	/* Unregister device */
 	nand_release(mtd_to_nand(mtd));