[RFC gpio/for-next 2/2] gpio: gpio-mux-input: add generic gpio input multiplexer

[Mauri Sandberg <sandberg@mailfence.com>]

Suppport for a general GPIO multiplexer. To drive the multiplexer a
mux-controller is needed. The output pin of the multiplexer is a GPIO
pin.

Signed-off-by: Mauri Sandberg <sandberg@mailfence.com>
---
 drivers/gpio/Kconfig          |  11 +++
 drivers/gpio/Makefile         |   1 +
 drivers/gpio/gpio-mux-input.c | 143 ++++++++++++++++++++++++++++++++++
 3 files changed, 155 insertions(+)
 create mode 100644 drivers/gpio/gpio-mux-input.c

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index c70f46e80a3b..41062d8f7d93 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1641,4 +1641,15 @@ config GPIO_MOCKUP
 
 endmenu
 
+comment "Other GPIO expanders"
+
+config GPIO_MUX_INPUT
+	tristate "General GPIO input multiplexer"
+	select MULTIPLEXER
+	select MUX_GPIO
+	depends on OF_GPIO
+	help
+	  Say yes here to enable support for generic GPIO input multiplexer. This
+	  needs a multiplexer controller to drive the select pins.
+
 endif
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 35e3b6026665..00f7576ce23f 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -105,6 +105,7 @@ obj-$(CONFIG_GPIO_MPC8XXX)		+= gpio-mpc8xxx.o
 obj-$(CONFIG_GPIO_MSC313)		+= gpio-msc313.o
 obj-$(CONFIG_GPIO_MSIC)			+= gpio-msic.o
 obj-$(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..ec0c7acbab2f
--- /dev/null
+++ b/drivers/gpio/gpio-mux-input.c
@@ -0,0 +1,143 @@
+// 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_direction_input(struct gpio_chip *gc,
+				       unsigned int offset)
+{
+	return 0;
+}
+
+static int gpio_mux_input_direction_output(struct gpio_chip *gc,
+					unsigned int offset, int val)
+{
+	return -EINVAL;
+}
+
+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 void gpio_mux_input_set_value(struct gpio_chip *gc,
+				  unsigned int offset, int val)
+{
+	/* not supported */
+}
+
+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 GPIOs: %d\n", err);
+		goto err_free_mc;
+	}
+
+	mux->mux_pin = pin;
+	mux->parent = &pdev->dev;
+
+	gc = &mux->gpio_chip;
+	gc->direction_input  = gpio_mux_input_direction_input;
+	gc->direction_output = gpio_mux_input_direction_output;
+	gc->get = gpio_mux_input_get_value;
+	gc->set = gpio_mux_input_set_value;
+	gc->can_sleep = 1;
+
+	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);
+	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",
+		.owner		= THIS_MODULE,
+		.of_match_table = gpio_mux_input_id,
+	},
+	.probe	= gpio_mux_input_probe,
+};
+module_platform_driver(gpio_mux_input_driver);
-- 
2.25.1