ath79: add gpio-latch driver for MikroTik RouterBOARDs

This is a slighty modified version of ar71xx gpio-latch driver
written by Gabor Juhos <juhosg@openwrt.org>.

Changes:
* DTS support,
* New gpio API (gpiod_*).

Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Signed-off-by: Denis Kalashnikov <denis281089@gmail.com>
(cherry-picked from commit 7b8931678c36c8d8c333b446258a653b1358bf70)

2 files changed, 226 insertions, 0 deletions

diff --git a/target/linux/ath79/files/drivers/gpio/gpio-latch.c b/target/linux/ath79/files/drivers/gpio/gpio-latch.c
new file mode 100644
index 0000000000..f3545a663e
--- /dev/null
+++ b/target/linux/ath79/files/drivers/gpio/gpio-latch.c
@@ -0,0 +1,203 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  GPIO latch driver
+ *
+ *  Copyright (C) 2014 Gabor Juhos <juhosg@openwrt.org>
+ */
+
+#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>
+
+#define GPIO_LATCH_DRIVER_NAME  "gpio-latch"
+#define GPIO_LATCH_LINES 9
+
+struct gpio_latch_chip {
+	struct gpio_chip gc;
+	struct mutex mutex;
+	struct mutex latch_mutex;
+	bool latch_enabled;
+	int le_gpio;
+	bool le_active_low;
+	struct gpio_desc *gpios[GPIO_LATCH_LINES];
+};
+
+static inline struct gpio_latch_chip *to_gpio_latch_chip(struct gpio_chip *gc)
+{
+	return container_of(gc, struct gpio_latch_chip, gc);
+}
+
+static void gpio_latch_lock(struct gpio_latch_chip *glc, bool enable)
+{
+	mutex_lock(&glc->mutex);
+
+	if (enable)
+		glc->latch_enabled = true;
+
+	if (glc->latch_enabled)
+		mutex_lock(&glc->latch_mutex);
+}
+
+static void gpio_latch_unlock(struct gpio_latch_chip *glc, bool disable)
+{
+	if (glc->latch_enabled)
+		mutex_unlock(&glc->latch_mutex);
+
+	if (disable)
+		glc->latch_enabled = true;
+
+	mutex_unlock(&glc->mutex);
+}
+
+static int
+gpio_latch_get(struct gpio_chip *gc, unsigned offset)
+{
+	struct gpio_latch_chip *glc = to_gpio_latch_chip(gc);
+	int ret;
+
+	gpio_latch_lock(glc, false);
+	ret = gpiod_get_value(glc->gpios[offset]);
+	gpio_latch_unlock(glc, false);
+
+	return ret;
+}
+
+static void
+gpio_latch_set(struct gpio_chip *gc, unsigned offset, int value)
+{
+	struct gpio_latch_chip *glc = to_gpio_latch_chip(gc);
+	bool enable_latch = false;
+	bool disable_latch = false;
+
+	if (offset == glc->le_gpio) {
+		enable_latch = value ^ glc->le_active_low;
+		disable_latch = !enable_latch;
+	}
+
+	gpio_latch_lock(glc, enable_latch);
+	gpiod_set_raw_value(glc->gpios[offset], value);
+	gpio_latch_unlock(glc, disable_latch);
+}
+
+static int
+gpio_latch_direction_output(struct gpio_chip *gc, unsigned offset, int value)
+{
+	struct gpio_latch_chip *glc = to_gpio_latch_chip(gc);
+	bool enable_latch = false;
+	bool disable_latch = false;
+	int ret;
+
+	if (offset == glc->le_gpio) {
+		enable_latch = value ^ glc->le_active_low;
+		disable_latch = !enable_latch;
+	}
+
+	gpio_latch_lock(glc, enable_latch);
+	ret = gpiod_direction_output_raw(glc->gpios[offset], value);
+	gpio_latch_unlock(glc, disable_latch);
+
+	return ret;
+}
+
+static int gpio_latch_probe(struct platform_device *pdev)
+{
+	struct gpio_latch_chip *glc;
+	struct gpio_chip *gc;
+	struct device *dev = &pdev->dev;
+	struct device_node *of_node = dev->of_node;
+	int i, n;
+
+	glc = devm_kzalloc(dev, sizeof(*glc), GFP_KERNEL);
+	if (!glc)
+		return -ENOMEM;
+
+	mutex_init(&glc->mutex);
+	mutex_init(&glc->latch_mutex);
+
+	n = gpiod_count(dev, NULL);
+	if (n <= 0) {
+		dev_err(dev, "failed to get gpios: %d\n", n);
+		return n;
+	} else if (n != GPIO_LATCH_LINES) {
+		dev_err(dev, "expected %d gpios\n", GPIO_LATCH_LINES);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < n; i++) {
+		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]));
+			return PTR_ERR(glc->gpios[i]);
+		}
+	}
+
+	glc->le_gpio = 8;
+	glc->le_active_low = gpiod_is_active_low(glc->gpios[glc->le_gpio]);
+
+	if (!glc->gpios[glc->le_gpio]) {
+		dev_err(dev, "missing required latch-enable gpio %d\n",
+			glc->le_gpio);
+		return -EINVAL;
+	}
+
+	gc = &glc->gc;
+	gc->label = GPIO_LATCH_DRIVER_NAME;
+	gc->can_sleep = true;
+	gc->base = -1;
+	gc->ngpio = GPIO_LATCH_LINES;
+	gc->get = gpio_latch_get;
+	gc->set = gpio_latch_set;
+	gc->direction_output = gpio_latch_direction_output;
+	gc->of_node = of_node;
+
+	platform_set_drvdata(pdev, glc);
+
+	i = gpiochip_add(&glc->gc);
+	if (i) {
+		dev_err(dev, "gpiochip_add() failed: %d\n", i);
+		return i;
+	}
+
+	return 0;
+}
+
+static int gpio_latch_remove(struct platform_device *pdev)
+{
+	struct gpio_latch_chip *glc = platform_get_drvdata(pdev);
+
+	gpiochip_remove(&glc->gc);
+	return 0;
+}
+
+static const struct of_device_id gpio_latch_match[] = {
+	{ .compatible = GPIO_LATCH_DRIVER_NAME },
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, gpio_latch_match);
+
+static struct platform_driver gpio_latch_driver = {
+	.probe = gpio_latch_probe,
+	.remove = gpio_latch_remove,
+	.driver = {
+		.name = GPIO_LATCH_DRIVER_NAME,
+		.owner = THIS_MODULE,
+		.of_match_table = gpio_latch_match,
+	},
+};
+
+module_platform_driver(gpio_latch_driver);
+
+MODULE_DESCRIPTION("GPIO latch driver");
+MODULE_AUTHOR("Gabor Juhos <juhosg@openwrt.org>");
+MODULE_AUTHOR("Denis Kalashnikov <denis281089@gmail.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:" GPIO_LATCH_DRIVER_NAME);
diff --git a/target/linux/ath79/patches-5.4/939-mikrotik-rb91x.patch b/target/linux/ath79/patches-5.4/939-mikrotik-rb91x.patch
new file mode 100644
index 0000000000..baeaab4611
--- /dev/null
+++ b/target/linux/ath79/patches-5.4/939-mikrotik-rb91x.patch
@@ -0,0 +1,23 @@
+--- a/drivers/gpio/Kconfig
++++ b/drivers/gpio/Kconfig
+@@ -130,6 +130,10 @@ config GPIO_ATH79
+ 	  Select this option to enable GPIO driver for
+ 	  Atheros AR71XX/AR724X/AR913X SoC devices.
+ 
++config GPIO_LATCH
++	tristate "MikroTik RouterBOARD GPIO latch support"
++	depends on ATH79
++
+ config GPIO_RASPBERRYPI_EXP
+ 	tristate "Raspberry Pi 3 GPIO Expander"
+ 	default RASPBERRYPI_FIRMWARE
+--- a/drivers/gpio/Makefile
++++ b/drivers/gpio/Makefile
+@@ -67,6 +67,7 @@ obj-$(CONFIG_GPIO_IT87)			+= gpio-it87.o
+ obj-$(CONFIG_GPIO_IXP4XX)		+= gpio-ixp4xx.o
+ obj-$(CONFIG_GPIO_JANZ_TTL)		+= gpio-janz-ttl.o
+ obj-$(CONFIG_GPIO_KEMPLD)		+= gpio-kempld.o
++obj-$(CONFIG_GPIO_LATCH)		+= gpio-latch.o
+ obj-$(CONFIG_GPIO_LOONGSON1)		+= gpio-loongson1.o
+ obj-$(CONFIG_GPIO_LOONGSON)		+= gpio-loongson.o
+ obj-$(CONFIG_GPIO_LP3943)		+= gpio-lp3943.o