wiegand: add Wiegand GPIO bitbanged controller driver

This controller formats the data to a Wiegand format and bit-bangs
the message on devicetree defined GPIO lines.

Several attributes need to be defined in the devicetree in order
for this driver to work, namely the data-hi-gpios, data-lo-gpios,
pulse-len, frame-gap and interval-len. These attributes are
documented in the devicetree bindings documentation files.

The driver creates a dev file for writing messages on the bus.
It also creates a sysfs file to control the payload length of
messages(in bits). If a message is shorter than the set payload
length, it will be discarded. On the other hand, if a message is
longer, the additional bits will be stripped off.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Martin Zaťovič <m.zatovic1@gmail.com>

Documentation/ABI/testing/sysfs-driver-wiegand-gpio

@@ -0,0 +1,9 @@
+What:		/sys/devices/platform/.../wiegand-gpio-attributes/payload_len
+Date:		January 2023
+Contact:	Martin Zaťovič <m.zatovic1@gmail.com>
+Description:
+		Read/set the payload length of messages sent by Wiegand GPIO
+		bit-banging controller in bits. The default value is 26, as
+		that is the most widely-used length of Wiegand messages.
+		Controller will only send messages of at least the set length
+		and it will strip off bits of longer messages.

MAINTAINERS

@@ -22432,7 +22432,9 @@ F:	include/linux/wiegand.h
 WIEGAND GPIO BITBANG DRIVER
 M:	Martin Zaťovič <m.zatovic1@gmail.com>
 S:	Maintained
+F:	Documentation/ABI/testing/sysfs-driver-wiegand-gpio
 F:	Documentation/devicetree/bindings/wiegand/wiegand-gpio.yaml
+F:	drivers/wiegand/wiegand-gpio.c
 
 WIIMOTE HID DRIVER
 M:	David Rheinsberg <david.rheinsberg@gmail.com>

drivers/wiegand/Kconfig

@@ -18,3 +18,11 @@ config WIEGAND
 	  are initially pulled up. When a bit of value 0 is being transmitted,
 	  the D0 line is pulled down. Similarly, when a bit of value 1 is being
 	  transmitted, the D1 line is pulled down.
+
+config WIEGAND_GPIO
+	tristate "GPIO-based wiegand master (write only)"
+	depends on WIEGAND
+	help
+	  This GPIO bitbanging Wiegand controller uses the libgpiod library to
+	  utilize GPIO lines for sending Wiegand data. Userspace may access
+	  the Wiegand GPIO interface via a dev entry.

drivers/wiegand/Makefile

@@ -1 +1,2 @@
 obj-$(CONFIG_WIEGAND)			+= wiegand.o
+obj-$(CONFIG_WIEGAND_GPIO)		+= wiegand-gpio.o

drivers/wiegand/wiegand-gpio.c

@@ -0,0 +1,316 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/poll.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/wiegand.h>
+
+#define WIEGAND_MAX_PAYLEN_BYTES 256
+
+struct wiegand_gpio {
+	struct device *dev;
+	struct wiegand_controller *ctlr;
+	struct miscdevice misc_dev;
+	struct mutex mutex;
+	struct gpio_desc *gpio_data_hi;
+	struct gpio_desc *gpio_data_lo;
+	struct file_operations fops;
+	u8 data[WIEGAND_MAX_PAYLEN_BYTES];
+};
+
+struct wiegand_gpio_instance {
+	struct wiegand_gpio *dev;
+	unsigned long flags;
+};
+
+static ssize_t store_ulong(u32 *val, const char *buf, size_t size, unsigned long max)
+{
+	int rc;
+	u32 new;
+
+	rc = kstrtou32(buf, 0, &new);
+	if (rc)
+		return rc;
+
+	if (max != 0 && new > max)
+		return -EINVAL;
+
+	*val = new;
+	return size;
+}
+
+/*
+ * Attribute file for setting payload length of Wiegand messages.
+ */
+ssize_t payload_len_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct wiegand_gpio *wiegand_gpio = dev_get_drvdata(dev);
+	struct wiegand_controller *ctlr = wiegand_gpio->ctlr;
+
+	return sysfs_emit(buf, "%u\n", ctlr->payload_len);
+}
+
+ssize_t payload_len_store(struct device *dev, struct device_attribute *attr, const char *buf,
+			size_t count)
+{
+	struct wiegand_gpio *wiegand_gpio = dev_get_drvdata(dev);
+	struct wiegand_controller *ctlr = wiegand_gpio->ctlr;
+
+	return store_ulong(&(ctlr->payload_len), buf, count, WIEGAND_MAX_PAYLEN_BYTES * 8);
+}
+DEVICE_ATTR_RW(payload_len);
+
+static struct attribute *wiegand_gpio_attrs[] = {
+	&dev_attr_payload_len.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(wiegand_gpio);
+
+/*
+ * To send a bit of value 1 following the wiegand protocol, one must set
+ * the wiegand_data_hi to low for the duration of pulse. Similarly to send
+ * a bit of value 0, the wiegand_data_lo is set to low for pulse duration.
+ * This way the two lines are never low at the same time.
+ */
+void wiegand_gpio_send_bit(struct wiegand_gpio *wiegand_gpio, bool value, bool last)
+{
+	u32 pulse_len = wiegand_gpio->ctlr->pulse_len;
+	u32 interval_len = wiegand_gpio->ctlr->interval_len;
+	u32 frame_gap = wiegand_gpio->ctlr->frame_gap;
+	struct gpio_desc *gpio = value ? wiegand_gpio->gpio_data_hi : wiegand_gpio->gpio_data_lo;
+
+	gpiod_set_value_cansleep(gpio, 0);
+	udelay(pulse_len);
+	gpiod_set_value_cansleep(gpio, 1);
+
+	if (last)
+		udelay(frame_gap - pulse_len);
+	else
+		udelay(interval_len - pulse_len);
+}
+
+/* This function is used for writing from file in dev directory */
+static int wiegand_gpio_write_by_bits(struct wiegand_gpio *wiegand_gpio, u16 bitlen)
+{
+	size_t i;
+	bool bit_value, is_last_bit;
+
+	for (i = 0; i < bitlen; i++) {
+		bit_value = ((wiegand_gpio->data[i / 8] >> (7 - (i % 8))) & 0x01);
+		is_last_bit = (i + 1) == bitlen;
+		wiegand_gpio_send_bit(wiegand_gpio, bit_value, is_last_bit);
+	}
+
+	return 0;
+}
+
+static ssize_t wiegand_gpio_get_user_data(struct wiegand_gpio *wiegand_gpio, char __user const *buf,
+					  size_t len)
+{
+	size_t rc;
+
+	if (len > WIEGAND_MAX_PAYLEN_BYTES)
+		return -EBADMSG;
+
+	rc = copy_from_user(&wiegand_gpio->data[0], buf, WIEGAND_MAX_PAYLEN_BYTES);
+	if (rc < 0)
+		return rc;
+
+	return len;
+}
+
+static int wiegand_gpio_frelease(struct inode *ino, struct file *filp)
+{
+	struct wiegand_gpio_instance *info = filp->private_data;
+	struct wiegand_gpio *wiegand_gpio = info->dev;
+
+	mutex_lock(&wiegand_gpio->mutex);
+	info->flags = 0;
+	mutex_unlock(&wiegand_gpio->mutex);
+
+	kfree(info);
+
+	return 0;
+}
+
+static ssize_t wiegand_gpio_fwrite(struct file *filp, char __user const *buf, size_t len,
+				loff_t *offset)
+{
+	struct wiegand_gpio_instance *info = filp->private_data;
+	struct wiegand_gpio *wiegand_gpio = info->dev;
+	u32 msg_length = wiegand_gpio->ctlr->payload_len;
+	int rc;
+
+	if (buf == NULL || len == 0 || len * 8 < msg_length)
+		return -EINVAL;
+
+	rc = wiegand_gpio_get_user_data(wiegand_gpio, buf, len);
+	if (rc < 0)
+		return rc;
+
+	wiegand_gpio_write_by_bits(wiegand_gpio, msg_length);
+
+	return len;
+}
+
+static int wiegand_gpio_fopen(struct inode *ino, struct file *filp)
+{
+	int rc;
+	struct wiegand_gpio_instance *info;
+	struct wiegand_gpio *wiegand_gpio = container_of(filp->f_op, struct wiegand_gpio, fops);
+
+	mutex_lock(&wiegand_gpio->mutex);
+
+	if ((filp->f_flags & O_ACCMODE) == O_RDONLY || (filp->f_flags & O_ACCMODE) == O_RDWR) {
+		dev_err(wiegand_gpio->dev, "Device is write only\n");
+		rc = -EIO;
+		goto err;
+	}
+
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
+	if (!info) {
+		rc = -ENOMEM;
+		goto err;
+	}
+
+	info->dev = wiegand_gpio;
+	info->flags = filp->f_flags;
+	mutex_unlock(&wiegand_gpio->mutex);
+
+	filp->private_data = info;
+
+	return 0;
+err:
+	mutex_unlock(&wiegand_gpio->mutex);
+	return rc;
+}
+
+/* This function is used by device drivers */
+int wiegand_gpio_transfer_message(struct wiegand_device *dev, u8 *message, u8 msg_bitlen)
+{
+	struct wiegand_controller *ctlr = dev->controller;
+	struct wiegand_gpio *wiegand_gpio = wiegand_master_get_devdata(ctlr);
+	u8 msg_bytelength = (msg_bitlen % 8) ? (msg_bitlen / 8) + 1 : (msg_bitlen / 8);
+
+	memcpy(wiegand_gpio->data, message, msg_bytelength);
+	wiegand_gpio_write_by_bits(wiegand_gpio, msg_bitlen);
+
+	return 0;
+}
+
+static int wiegand_gpio_request(struct device *dev, struct wiegand_gpio *wiegand_gpio)
+{
+	/* Get GPIO lines using device tree bindings. */
+	wiegand_gpio->gpio_data_lo = devm_gpiod_get(dev, "data-lo", GPIOD_OUT_HIGH);
+	if (IS_ERR(wiegand_gpio->gpio_data_lo))
+		return PTR_ERR(wiegand_gpio->gpio_data_lo);
+
+	wiegand_gpio->gpio_data_hi = devm_gpiod_get(dev, "data-hi", GPIOD_OUT_HIGH);
+	return PTR_ERR_OR_ZERO(wiegand_gpio->gpio_data_hi);
+}
+
+static int wiegand_gpio_probe(struct platform_device *device)
+{
+	int status;
+	struct wiegand_controller *master;
+	struct wiegand_gpio *wiegand_gpio;
+	struct device *dev = &device->dev;
+
+	master = devm_wiegand_alloc_master(dev, sizeof(*wiegand_gpio));
+	if (!master)
+		return -ENOMEM;
+
+	if (dev->of_node)
+		master->dev.of_node = device->dev.of_node;
+
+	if (status)
+		return status;
+
+	master->transfer_message = &wiegand_gpio_transfer_message;
+	master->payload_len = 26; /* set standard 26-bit format */
+
+	wiegand_gpio = wiegand_master_get_devdata(master);
+	wiegand_gpio->ctlr = master;
+	wiegand_gpio->fops.owner = THIS_MODULE;
+	wiegand_gpio->fops.open = wiegand_gpio_fopen;
+	wiegand_gpio->fops.release = wiegand_gpio_frelease;
+	wiegand_gpio->fops.write = wiegand_gpio_fwrite;
+
+	platform_set_drvdata(device, wiegand_gpio);
+
+	master->bus_num = device->id;
+	wiegand_gpio->dev = dev;
+
+	mutex_init(&wiegand_gpio->mutex);
+
+	status = wiegand_gpio_request(dev, wiegand_gpio);
+	if (status) {
+		dev_err(wiegand_gpio->dev, "failed at requesting GPIOs\n");
+		return status;
+	}
+
+	status = gpiod_direction_output(wiegand_gpio->gpio_data_hi, 1);
+	status |= gpiod_direction_output(wiegand_gpio->gpio_data_lo, 1);
+	if (status) {
+		dev_err(wiegand_gpio->dev, "failed to set GPIOs direction\n");
+		return status;
+	}
+
+	status = devm_wiegand_register_master(dev, master);
+	if (status) {
+		dev_err(wiegand_gpio->dev, "failed to register master\n");
+		return status;
+	}
+
+	wiegand_gpio->misc_dev.name = kasprintf(GFP_KERNEL, "wiegand-gpio%u", master->bus_num);
+	wiegand_gpio->misc_dev.minor = MISC_DYNAMIC_MINOR;
+	wiegand_gpio->misc_dev.fops = &wiegand_gpio->fops;
+
+	status = misc_register(&wiegand_gpio->misc_dev);
+	if (status) {
+		dev_err(wiegand_gpio->dev, "couldn't register misc device\n");
+		return status;
+	}
+	wiegand_gpio->misc_dev.parent = wiegand_gpio->dev;
+
+	device_create_file(dev, &dev_attr_payload_len);
+	dev->groups = wiegand_gpio_groups;
+
+	return status;
+}
+
+static int wiegand_gpio_remove(struct platform_device *device)
+{
+	struct wiegand_gpio *wiegand_gpio = platform_get_drvdata(device);
+
+	misc_deregister(&wiegand_gpio->misc_dev);
+
+	return 0;
+}
+
+static const struct of_device_id wiegand_gpio_dt_idtable[] = {
+	{ .compatible = "wiegand-gpio", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, wiegand_gpio_dt_idtable);
+
+static struct platform_driver wiegand_gpio_driver = {
+	.driver = {
+		.name	= "wiegand-gpio",
+		.of_match_table = wiegand_gpio_dt_idtable,
+	},
+	.probe		= wiegand_gpio_probe,
+	.remove		= wiegand_gpio_remove,
+};
+
+module_platform_driver(wiegand_gpio_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Wiegand write-only driver realized by GPIOs");
+MODULE_AUTHOR("Martin Zaťovič <m.zatovic1@gmail.com>");