ath79: add support for reset key on MikroTik RB912UAG-2HPnD

On MikroTik RB91x board series a reset key shares SoC gpio
line #15 with NAND ALE and NAND IO7. So we need a custom
gpio driver to manage this non-trivial connection schema.
Also rb91x-nand needs to have an ability to disable a polling
of the key while it works with NAND.

While we've been integrating rb91x-key into a firmware, we've
figured out that:
* In the gpio-latch driver we need to add a "cansleep" suffix to
several gpiolib calls,
* When gpio-latch and rb91x-nand fail to get a gpio and an error
is -EPROBE_DEFER, they shouldn't report about this, since this
actually is not an error and occurs when the gpio-latch probe
function is called before the rb91x-key probe.
We fix these related things here too.

Signed-off-by: Denis Kalashnikov <denis281089@gmail.com>
Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Tested-by: Koen Vandeputte <koen.vandeputte@ncentric.com>

target/linux/ath79/files/drivers/gpio/gpio-latch.c

@@ -62,7 +62,7 @@ gpio_latch_get(struct gpio_chip *gc, unsigned offset)
 	int ret;
 
 	gpio_latch_lock(glc, false);
-	ret = gpiod_get_value(glc->gpios[offset]);
+	ret = gpiod_get_raw_value_cansleep(glc->gpios[offset]);
 	gpio_latch_unlock(glc, false);
 
 	return ret;
@@ -81,7 +81,7 @@ gpio_latch_set(struct gpio_chip *gc, unsigned offset, int value)
 	}
 
 	gpio_latch_lock(glc, enable_latch);
-	gpiod_set_raw_value(glc->gpios[offset], value);
+	gpiod_set_raw_value_cansleep(glc->gpios[offset], value);
 	gpio_latch_unlock(glc, disable_latch);
 }
 
@@ -133,8 +133,10 @@ static int gpio_latch_probe(struct platform_device *pdev)
 		glc->gpios[i] = devm_gpiod_get_index_optional(dev, NULL, i,
 			GPIOD_OUT_LOW);
 		if (IS_ERR(glc->gpios[i])) {
-			dev_err(dev, "failed to get gpio %d: %d\n", i,
-				PTR_ERR(glc->gpios[i]));
+			if (PTR_ERR(glc->gpios[i]) != -EPROBE_DEFER) {
+				dev_err(dev, "failed to get gpio %d: %d\n", i,
+					PTR_ERR(glc->gpios[i]));
+			}
 			return PTR_ERR(glc->gpios[i]);
 		}
 	}

target/linux/ath79/files/drivers/gpio/gpio-rb91x-key.c

@@ -0,0 +1,218 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Driver for reset key gpio line on MikroTik RB91x board series.
+ * This line is shared between NAND ALE (goes through a latch),
+ * NAND IO7 and reset key. We make 3 virtual gpio lines from the
+ * single physical one:
+ *   1) Capable output one for NAND,
+ *   2) Capable input one for reset key,
+ *   3) And capable output one, aka "key-poll-disable",
+ *      for NAND -- to syncronise NAND operation and key polling.
+ *
+ * Copyright (C) 2021 Denis Kalashnikov <denis281089@gmail.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/platform_device.h>
+#include <linux/of_platform.h>
+#include <linux/of_gpio.h>
+#include <linux/delay.h>
+
+#define GPIO_RB91X_KEY_DRIVER_NAME  "gpio-rb91x-key"
+
+enum gpio_rb91x_key_gpios {
+	GPIO_RB91X_KEY_NAND,
+	GPIO_RB91X_KEY_POLL,
+	GPIO_RB91X_KEY_PDIS,
+
+	GPIO_RB91X_KEY_NGPIOS,
+};
+
+struct gpio_rb91x_key {
+	struct gpio_chip gc;
+	struct mutex mutex;
+	struct mutex poll_mutex;
+	int polling_disabled;
+	struct gpio_desc *gpio;
+};
+
+static inline struct gpio_rb91x_key *to_gpio_rb91x_key(struct gpio_chip *gc)
+{
+	return container_of(gc, struct gpio_rb91x_key, gc);
+}
+
+static int gpio_rb91x_key_get(struct gpio_chip *gc, unsigned offset)
+{
+	struct gpio_rb91x_key *drvdata = to_gpio_rb91x_key(gc);
+	struct gpio_desc *gpio = drvdata->gpio;
+	int val, bak_val;
+
+	switch (offset) {
+	case GPIO_RB91X_KEY_NAND:
+		mutex_lock(&drvdata->mutex);
+		val = gpiod_get_value_cansleep(gpio);
+		mutex_unlock(&drvdata->mutex);
+		break;
+	case GPIO_RB91X_KEY_PDIS:
+		mutex_lock(&drvdata->mutex);
+		val = drvdata->polling_disabled;
+		mutex_unlock(&drvdata->mutex);
+		break;
+	case GPIO_RB91X_KEY_POLL:
+		mutex_lock(&drvdata->poll_mutex);
+		mutex_lock(&drvdata->mutex);
+		bak_val = gpiod_get_raw_value_cansleep(gpio);
+		gpiod_direction_input(gpio);
+		/*
+		 * Without this delay nothing works. Get it
+		 * from mikrotik RouterOS linux kernel patches.
+		 */
+		udelay(200);
+		val = gpiod_get_raw_value_cansleep(gpio);
+		gpiod_direction_output_raw(gpio, bak_val);
+		mutex_unlock(&drvdata->mutex);
+		mutex_unlock(&drvdata->poll_mutex);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return val;
+}
+
+static int gpio_rb91x_key_direction_input(struct gpio_chip *gc, unsigned offset)
+{
+	switch (offset) {
+	case GPIO_RB91X_KEY_POLL:
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+static void gpio_rb91x_key_set(struct gpio_chip *gc, unsigned offset, int value)
+{
+	struct gpio_rb91x_key *drvdata = to_gpio_rb91x_key(gc);
+	struct gpio_desc *gpio = drvdata->gpio;
+
+	mutex_lock(&drvdata->mutex);
+
+	switch (offset) {
+	case GPIO_RB91X_KEY_NAND:
+		gpiod_set_raw_value_cansleep(gpio, value);
+		break;
+	case GPIO_RB91X_KEY_PDIS:
+		if (value) {
+			if (!drvdata->polling_disabled) {
+				mutex_lock(&drvdata->poll_mutex);
+				drvdata->polling_disabled = 1;
+			}
+		} else {
+			if (drvdata->polling_disabled) {
+				mutex_unlock(&drvdata->poll_mutex);
+				drvdata->polling_disabled = 0;
+			}
+		}
+		break;
+	default:
+		break;
+	}
+
+	mutex_unlock(&drvdata->mutex);
+}
+
+static int gpio_rb91x_key_direction_output(struct gpio_chip *gc, unsigned offset,
+					   int value)
+{
+	switch (offset) {
+	case GPIO_RB91X_KEY_NAND:
+	case GPIO_RB91X_KEY_PDIS:
+		gpio_rb91x_key_set(gc, offset, value);
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int gpio_rb91x_key_probe(struct platform_device *pdev)
+{
+	struct gpio_rb91x_key *drvdata;
+	struct gpio_chip *gc;
+	struct device *dev = &pdev->dev;
+	struct device_node *of_node = dev->of_node;
+	int r;
+
+	drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
+	if (!drvdata)
+		return -ENOMEM;
+
+	mutex_init(&drvdata->mutex);
+	mutex_init(&drvdata->poll_mutex);
+
+	drvdata->gpio = devm_gpiod_get(dev, NULL, GPIOD_OUT_LOW);
+	if (IS_ERR(drvdata->gpio)) {
+		if (PTR_ERR(drvdata->gpio) != -EPROBE_DEFER) {
+			dev_err(dev, "failed to get gpio: %ld\n",
+				PTR_ERR(drvdata->gpio));
+		}
+		return PTR_ERR(drvdata->gpio);
+	}
+
+	gc = &drvdata->gc;
+	gc->label = GPIO_RB91X_KEY_DRIVER_NAME;
+	gc->can_sleep = 1;
+	gc->base = -1;
+	gc->ngpio = GPIO_RB91X_KEY_NGPIOS;
+	gc->get = gpio_rb91x_key_get;
+	gc->set = gpio_rb91x_key_set;
+	gc->direction_output = gpio_rb91x_key_direction_output;
+	gc->direction_input = gpio_rb91x_key_direction_input;
+	gc->of_node = of_node;
+
+	platform_set_drvdata(pdev, drvdata);
+
+	r = gpiochip_add(&drvdata->gc);
+	if (r) {
+		dev_err(dev, "gpiochip_add() failed: %d\n", r);
+		return r;
+	}
+
+	return 0;
+}
+
+static int gpio_rb91x_key_remove(struct platform_device *pdev)
+{
+	struct gpio_rb91x_key *drvdata = platform_get_drvdata(pdev);
+
+	gpiochip_remove(&drvdata->gc);
+	return 0;
+}
+
+static const struct of_device_id gpio_rb91x_key_match[] = {
+	{ .compatible = "mikrotik,"GPIO_RB91X_KEY_DRIVER_NAME },
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, gpio_rb91x_key_match);
+
+static struct platform_driver gpio_rb91x_key_driver = {
+	.probe = gpio_rb91x_key_probe,
+	.remove = gpio_rb91x_key_remove,
+	.driver = {
+		.name = GPIO_RB91X_KEY_DRIVER_NAME,
+		.owner = THIS_MODULE,
+		.of_match_table = gpio_rb91x_key_match,
+	},
+};
+
+module_platform_driver(gpio_rb91x_key_driver);
+
+MODULE_DESCRIPTION("Driver for reset key gpio line shared with NAND for MikroTik RB91x board series.");
+MODULE_AUTHOR("Denis Kalashnikov <denis281089@gmail.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:" GPIO_RB91X_KEY_DRIVER_NAME);

target/linux/ath79/files/drivers/mtd/nand/raw/rb91x_nand.c

@@ -40,6 +40,7 @@ enum rb91x_nand_gpios {
 	RB91X_NAND_ALE, /* Address Latch Enable */
 	RB91X_NAND_NRW, /* Read/Write. Active low */
 	RB91X_NAND_NLE, /* Latch Enable. Active low */
+	RB91X_NAND_PDIS, /* Reset Key Poll Disable. Active high */
 
 	RB91X_NAND_GPIOS,
 };
@@ -57,6 +58,12 @@ static inline void rb91x_nand_latch_lock(struct rb91x_nand_drvdata *drvdata,
 	gpiod_set_value_cansleep(drvdata->gpio[RB91X_NAND_NLE], lock);
 }
 
+static inline void rb91x_nand_rst_key_poll_disable(struct rb91x_nand_drvdata *drvdata,
+						   int disable)
+{
+	gpiod_set_value_cansleep(drvdata->gpio[RB91X_NAND_PDIS], disable);
+}
+
 static int rb91x_ooblayout_ecc(struct mtd_info *mtd, int section,
 			       struct mtd_oob_region *oobregion)
 {
@@ -115,6 +122,7 @@ static void rb91x_nand_write(struct rb91x_nand_drvdata *drvdata,
 	unsigned i;
 
 	rb91x_nand_latch_lock(drvdata, 1);
+	rb91x_nand_rst_key_poll_disable(drvdata, 1);
 
 	oe_reg = __raw_readl(base + AR71XX_GPIO_REG_OE);
 	out_reg = __raw_readl(base + AR71XX_GPIO_REG_OUT);
@@ -146,6 +154,7 @@ static void rb91x_nand_write(struct rb91x_nand_drvdata *drvdata,
 	/* Flush write */
 	__raw_readl(base + AR71XX_GPIO_REG_OUT);
 
+	rb91x_nand_rst_key_poll_disable(drvdata, 0);
 	rb91x_nand_latch_lock(drvdata, 0);
 }
 
@@ -162,6 +171,7 @@ static void rb91x_nand_read(struct rb91x_nand_drvdata *drvdata,
 	gpiod_set_value_cansleep(drvdata->gpio[RB91X_NAND_READ], 1);
 
 	rb91x_nand_latch_lock(drvdata, 1);
+	rb91x_nand_rst_key_poll_disable(drvdata, 1);
 
 	/* Save registers */
 	oe_reg = __raw_readl(base + AR71XX_GPIO_REG_OE);
@@ -199,6 +209,7 @@ static void rb91x_nand_read(struct rb91x_nand_drvdata *drvdata,
 	/* Flush write */
 	__raw_readl(base + AR71XX_GPIO_REG_OUT);
 
+	rb91x_nand_rst_key_poll_disable(drvdata, 0);
 	rb91x_nand_latch_lock(drvdata, 0);
 
 	/* Disable read mode */
@@ -274,8 +285,11 @@ static int rb91x_nand_probe(struct platform_device *pdev)
 
 	gpios = gpiod_get_array(dev, NULL, GPIOD_OUT_LOW);
 	if (IS_ERR(gpios)) {
-		dev_err(dev, "failed to get gpios: %d\n", (int)gpios);
-		return -EINVAL;
+		if (PTR_ERR(gpios) != -EPROBE_DEFER) {
+			dev_err(dev, "failed to get gpios: %d\n",
+				PTR_ERR(gpios));
+		}
+		return PTR_ERR(gpios);
 	}
 
 	if (gpios->ndescs != RB91X_NAND_GPIOS) {