gpio: Add gpio delay driver

This driver implements a GPIO enable/disable delay. It supports a list
of GPIO outputs, which ramp-up/ramp-down delay can be specified at
consumer location.
The main purpose is to address external, passive delays upon line
voltage changes.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/gpio/Kconfig

@@ -1733,6 +1733,14 @@ config GPIO_AGGREGATOR
 	      industrial control context, to be operated from userspace using
 	      the GPIO chardev interface.
 
+config GPIO_DELAY
+	tristate "GPIO delay"
+	help
+	  Say yes here to enable the GPIO delay, which provides a way to
+	  configure platform specific delays for GPIO ramp-up or ramp-down
+	  delays. This can serve the following purposes:
+	    - Open-drain output using an RC filter
+
 config GPIO_LATCH
 	tristate "GPIO latch driver"
 	help

drivers/gpio/Makefile

@@ -52,6 +52,7 @@ obj-$(CONFIG_GPIO_DA9052)		+= gpio-da9052.o
 obj-$(CONFIG_GPIO_DA9055)		+= gpio-da9055.o
 obj-$(CONFIG_GPIO_DAVINCI)		+= gpio-davinci.o
 obj-$(CONFIG_GPIO_DLN2)			+= gpio-dln2.o
+obj-$(CONFIG_GPIO_DELAY)		+= gpio-delay.o
 obj-$(CONFIG_GPIO_DWAPB)		+= gpio-dwapb.o
 obj-$(CONFIG_GPIO_EIC_SPRD)		+= gpio-eic-sprd.o
 obj-$(CONFIG_GPIO_ELKHARTLAKE)		+= gpio-elkhartlake.o

drivers/gpio/gpio-delay.c

@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2022 TQ-Systems GmbH
+ * Author: Alexander Stein <linux@ew.tq-group.com>
+ */
+
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/delay.h>
+
+#include "gpiolib.h"
+
+struct gpio_delay_timing {
+	unsigned long ramp_up_delay_us;
+	unsigned long ramp_down_delay_us;
+};
+
+struct gpio_delay_priv {
+	struct gpio_chip gc;
+	struct gpio_descs *input_gpio;
+	struct gpio_delay_timing *delay_timings;
+};
+
+static int gpio_delay_get_direction(struct gpio_chip *gc, unsigned int offset)
+{
+	return GPIO_LINE_DIRECTION_OUT;
+}
+
+static void gpio_delay_set(struct gpio_chip *gc, unsigned int offset, int val)
+{
+	struct gpio_delay_priv *priv = gpiochip_get_data(gc);
+	struct gpio_desc *gpio_desc = priv->input_gpio->desc[offset];
+	const struct gpio_delay_timing *delay_timings;
+	bool ramp_up;
+
+	gpiod_set_value(gpio_desc, val);
+
+	delay_timings = &priv->delay_timings[offset];
+	ramp_up = (!gpiod_is_active_low(gpio_desc) && val) ||
+		  (gpiod_is_active_low(gpio_desc) && !val);
+
+	if (ramp_up && delay_timings->ramp_up_delay_us)
+		udelay(delay_timings->ramp_up_delay_us);
+	if (!ramp_up && delay_timings->ramp_down_delay_us)
+		udelay(delay_timings->ramp_down_delay_us);
+}
+
+static void gpio_delay_set_can_sleep(struct gpio_chip *gc, unsigned int offset, int val)
+{
+	struct gpio_delay_priv *priv = gpiochip_get_data(gc);
+	struct gpio_desc *gpio_desc = priv->input_gpio->desc[offset];
+	const struct gpio_delay_timing *delay_timings;
+	bool ramp_up;
+
+	gpiod_set_value_cansleep(gpio_desc, val);
+
+	delay_timings = &priv->delay_timings[offset];
+	ramp_up = (!gpiod_is_active_low(gpio_desc) && val) ||
+		  (gpiod_is_active_low(gpio_desc) && !val);
+
+	if (ramp_up && delay_timings->ramp_up_delay_us)
+		fsleep(delay_timings->ramp_up_delay_us);
+	if (!ramp_up && delay_timings->ramp_down_delay_us)
+		fsleep(delay_timings->ramp_down_delay_us);
+}
+
+static int gpio_delay_of_xlate(struct gpio_chip *gc,
+			       const struct of_phandle_args *gpiospec,
+			       u32 *flags)
+{
+	struct gpio_delay_priv *priv = gpiochip_get_data(gc);
+	struct gpio_delay_timing *timings;
+	u32 line;
+
+	if (gpiospec->args_count != gc->of_gpio_n_cells)
+		return -EINVAL;
+
+	line = gpiospec->args[0];
+	if (line >= gc->ngpio)
+		return -EINVAL;
+
+	timings = &priv->delay_timings[line];
+	timings->ramp_up_delay_us = gpiospec->args[1];
+	timings->ramp_down_delay_us = gpiospec->args[2];
+
+	return line;
+}
+
+static bool gpio_delay_can_sleep(const struct gpio_delay_priv *priv)
+{
+	int i;
+
+	for (i = 0; i < priv->input_gpio->ndescs; i++)
+		if (gpiod_cansleep(priv->input_gpio->desc[i]))
+			return true;
+
+	return false;
+}
+
+static int gpio_delay_probe(struct platform_device *pdev)
+{
+	struct gpio_delay_priv *priv;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->input_gpio = devm_gpiod_get_array(&pdev->dev, NULL, GPIOD_OUT_LOW);
+	if (IS_ERR(priv->input_gpio))
+		return dev_err_probe(&pdev->dev, PTR_ERR(priv->input_gpio),
+				     "Failed to get input-gpios");
+
+	priv->delay_timings = devm_kcalloc(&pdev->dev,
+					   priv->input_gpio->ndescs,
+					   sizeof(*priv->delay_timings),
+					   GFP_KERNEL);
+	if (!priv->delay_timings)
+		return -ENOMEM;
+
+	if (gpio_delay_can_sleep(priv)) {
+		priv->gc.can_sleep = true;
+		priv->gc.set = gpio_delay_set_can_sleep;
+	} else {
+		priv->gc.can_sleep = false;
+		priv->gc.set = gpio_delay_set;
+	}
+
+	priv->gc.get_direction = gpio_delay_get_direction;
+	priv->gc.of_xlate = gpio_delay_of_xlate;
+	priv->gc.of_gpio_n_cells = 3;
+	priv->gc.ngpio = priv->input_gpio->ndescs;
+	priv->gc.owner = THIS_MODULE;
+	priv->gc.base = -1;
+	priv->gc.parent = &pdev->dev;
+
+	platform_set_drvdata(pdev, priv);
+
+	return devm_gpiochip_add_data(&pdev->dev, &priv->gc, priv);
+}
+
+static const struct of_device_id gpio_delay_ids[] = {
+	{
+		.compatible = "gpio-delay",
+	},
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, gpio_delay_ids);
+
+static struct platform_driver gpio_delay_driver = {
+	.driver	= {
+		.name		= "gpio-delay",
+		.of_match_table	= gpio_delay_ids,
+	},
+	.probe	= gpio_delay_probe,
+};
+module_platform_driver(gpio_delay_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Alexander Stein <alexander.stein@ew.tq-group.com>");
+MODULE_DESCRIPTION("GPIO delay driver");