[RFC,v2,2/2] gpio: gpio-mux-input: add generic gpio input multiplexer

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index b6b6150d0d04..7bf8021e0239 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1643,4 +1643,17 @@  config GPIO_SIM
 
 endmenu
 
+comment "Other GPIO expanders"
+
+config GPIO_MUX_INPUT
+	tristate "General GPIO input multiplexer"
+	depends on OF_GPIO
+	select MULTIPLEXER
+	select MUX_GPIO
+	help
+	  Say yes here to enable support for generic GPIO input multiplexer.
+
+  	  This driver uses a mux-controller to drive the multiplexer and has a
+  	  single output pin for reading the inputs to the mux.
+
 endif
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index d717aa85f8e1..e843e1bcfc20 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -103,6 +103,7 @@  obj-$(CONFIG_GPIO_MPC5200)		+= gpio-mpc5200.o
 obj-$(CONFIG_GPIO_MPC8XXX)		+= gpio-mpc8xxx.o
 obj-$(CONFIG_GPIO_MSC313)		+= gpio-msc313.o
 obj-$(CONFIG_GPIO_MT7621)		+= gpio-mt7621.o
+obj-$(CONFIG_GPIO_MUX_INPUT)		+= gpio-mux-input.o
 obj-$(CONFIG_GPIO_MVEBU)		+= gpio-mvebu.o
 obj-$(CONFIG_GPIO_MXC)			+= gpio-mxc.o
 obj-$(CONFIG_GPIO_MXS)			+= gpio-mxs.o
diff --git a/drivers/gpio/gpio-mux-input.c b/drivers/gpio/gpio-mux-input.c
new file mode 100644
index 000000000000..2de198a84bb9
--- /dev/null
+++ b/drivers/gpio/gpio-mux-input.c
@@ -0,0 +1,134 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  A generic GPIO input multiplexer driver
+ *
+ *  Copyright (C) 2021 Mauri Sandberg <sandberg@mailfence.com>
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/slab.h>
+#include <linux/platform_device.h>
+#include <linux/mux/consumer.h>
+
+struct gpio_mux_input {
+	struct device		*parent;
+	struct gpio_chip	gpio_chip;
+	struct mux_control	*mux_control;
+	struct gpio_desc	*mux_pin;
+};
+
+static struct gpio_mux_input *gpio_to_mux(struct gpio_chip *gc)
+{
+	return container_of(gc, struct gpio_mux_input, gpio_chip);
+}
+
+static int gpio_mux_input_get_direction(struct gpio_chip *gc,
+					unsigned int offset)
+{
+	return GPIO_LINE_DIRECTION_IN;
+}
+
+static int gpio_mux_input_get_value(struct gpio_chip *gc, unsigned int offset)
+{
+	struct gpio_mux_input *mux;
+	int ret;
+
+	mux = gpio_to_mux(gc);
+	ret = mux_control_select(mux->mux_control, offset);
+	if (ret)
+		return ret;
+
+	ret = gpiod_get_value(mux->mux_pin);
+	mux_control_deselect(mux->mux_control);
+	return ret;
+}
+
+static int gpio_mux_input_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct gpio_mux_input *mux;
+	struct gpio_chip *gc;
+	struct mux_control *mc;
+	struct gpio_desc *pin;
+	int err;
+
+	mux = kzalloc(sizeof(struct gpio_mux_input), GFP_KERNEL);
+	if (mux == NULL)
+		return -ENOMEM;
+
+	mc = mux_control_get(&pdev->dev, NULL);
+	if (IS_ERR(mc)) {
+		err = (int) PTR_ERR(mc);
+		if (err != -EPROBE_DEFER)
+			dev_err(&pdev->dev, "unable to get mux-control: %d\n",
+				err);
+		goto err_free_mux;
+	}
+
+	mux->mux_control = mc;
+	pin = gpiod_get(&pdev->dev, "pin",  GPIOD_IN);
+	if (IS_ERR(pin)) {
+		err = (int) PTR_ERR(pin);
+		dev_err(&pdev->dev, "unable to claim pin GPIO: %d\n", err);
+		goto err_free_mc;
+	}
+
+	mux->mux_pin = pin;
+	mux->parent = &pdev->dev;
+
+	gc = &mux->gpio_chip;
+	gc->get = gpio_mux_input_get_value;
+	gc->get_direction = gpio_mux_input_get_direction;
+
+	gc->base = -1;
+	gc->ngpio = mux_control_states(mc);
+	gc->label = dev_name(mux->parent);
+	gc->parent = mux->parent;
+	gc->owner = THIS_MODULE;
+	gc->of_node = np;
+
+	err = gpiochip_add(&mux->gpio_chip);
+	if (err) {
+		dev_err(&pdev->dev, "unable to add gpio chip, err=%d\n", err);
+		goto err_free_pin;
+	}
+
+	platform_set_drvdata(pdev, mux);
+
+	dev_info(&pdev->dev, "registered %u input GPIOs\n", gc->ngpio);
+
+	return 0;
+
+err_free_pin:
+	gpiod_put(pin);
+err_free_mc:
+	mux_control_put(mc);
+err_free_mux:
+	kfree(mux);
+	return err;
+}
+
+static const struct of_device_id gpio_mux_input_id[] = {
+	{
+		.compatible = "gpio-mux-input",
+		.data = NULL,
+	},
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, gpio_mux_input_id);
+
+static struct platform_driver gpio_mux_input_driver = {
+	.driver	= {
+		.name		= "gpio-mux-input",
+		.of_match_table = gpio_mux_input_id,
+	},
+	.probe	= gpio_mux_input_probe,
+};
+module_platform_driver(gpio_mux_input_driver);
+
+MODULE_AUTHOR("Mauri Sandberg <sandberg@mailfence.com>");
+MODULE_DESCRIPTION("Generic GPIO input multiplexer");
+MODULE_LICENSE("GPL");