Re: [PATCHv3 4/4] wiegand: add Wiegand GPIO bitbanged controller driver

From: Evgeny Boger
Date: Sun Mar 12 2023 - 06:32:42 EST

On 3/1/23 17:28, Martin Zaťovič wrote:
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@xxxxxxxxxx>
Signed-off-by: Martin Zaťovič <m.zatovic1@xxxxxxxxx>
---
.../ABI/testing/sysfs-driver-wiegand-gpio | 9 +
MAINTAINERS | 2 +
drivers/wiegand/Kconfig | 8 +
drivers/wiegand/Makefile | 1 +
drivers/wiegand/wiegand-gpio.c | 316 ++++++++++++++++++
5 files changed, 336 insertions(+)
create mode 100644 Documentation/ABI/testing/sysfs-driver-wiegand-gpio
create mode 100644 drivers/wiegand/wiegand-gpio.c

diff --git a/Documentation/ABI/testing/sysfs-driver-wiegand-gpio b/Documentation/ABI/testing/sysfs-driver-wiegand-gpio
new file mode 100644
index 000000000000..be2246880a83
--- /dev/null
+++ b/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@xxxxxxxxx>
+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.
diff --git a/MAINTAINERS b/MAINTAINERS
index 91e573466d6b..eeeb343ee91c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -22522,7 +22522,9 @@ F: include/linux/wiegand.h
WIEGAND GPIO BITBANG DRIVER
M: Martin Zaťovič <m.zatovic1@xxxxxxxxx>
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@xxxxxxxxx>
diff --git a/drivers/wiegand/Kconfig b/drivers/wiegand/Kconfig
index d6b63250e80b..d3a6c773c767 100644
--- a/drivers/wiegand/Kconfig
+++ b/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.
diff --git a/drivers/wiegand/Makefile b/drivers/wiegand/Makefile
index d17ecb722c6e..ddf697e21088 100644
--- a/drivers/wiegand/Makefile
+++ b/drivers/wiegand/Makefile
@@ -1 +1,2 @@
obj-$(CONFIG_WIEGAND) += wiegand.o
+obj-$(CONFIG_WIEGAND_GPIO) += wiegand-gpio.o
diff --git a/drivers/wiegand/wiegand-gpio.c b/drivers/wiegand/wiegand-gpio.c
new file mode 100644
index 000000000000..e67a30a1c5ae
--- /dev/null
+++ b/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];
maybe use bitmap for this?
+};
+
+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);
As far as I understand, Wiegand GPIO bit-banged driver is just one of the many possible driver implementations. I can imagine having dedicated hardware to send Wiegand messages. So it seems a little strange to have chardev API implemented in the bit-banged driver and not in the core, so it's common for all possible driver implementations.

+ 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@xxxxxxxxx>");

--
Kind regards,
Evgeny Boger
CTO @ Wiren Board