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    Subject[PATCH v3] leds: Introduce userspace leds driver
    Date
    This driver creates a userspace leds driver similar to uinput.

    New leds are created by opening /dev/uleds and writing a uleds_user_dev
    struct. A new leds class device is registered with the name given in the
    struct. Reading will return a single byte that is the current brightness.
    The poll() syscall is also supported. It will be triggered whenever the
    brightness changes. Closing the file handle to /dev/uleds will remove
    the leds class device.

    Signed-off-by: David Lechner <david@lechnology.com>
    ---

    v2 changes:

    * sort #includes
    * fix typo in Kconfig
    * Add Documentation text file

    v3 changes:

    * fix typos in docs
    * rename "leds class" to "LED class" in docs
    * rebase on linux-leds/for-next


    Documentation/leds/uleds.txt | 105 ++++++++++++++++++++
    drivers/leds/Kconfig | 8 ++
    drivers/leds/Makefile | 3 +
    drivers/leds/uleds.c | 224 +++++++++++++++++++++++++++++++++++++++++++
    include/uapi/linux/Kbuild | 1 +
    include/uapi/linux/uleds.h | 23 +++++
    6 files changed, 364 insertions(+)
    create mode 100644 Documentation/leds/uleds.txt
    create mode 100644 drivers/leds/uleds.c
    create mode 100644 include/uapi/linux/uleds.h

    diff --git a/Documentation/leds/uleds.txt b/Documentation/leds/uleds.txt
    new file mode 100644
    index 0000000..de11dbb
    --- /dev/null
    +++ b/Documentation/leds/uleds.txt
    @@ -0,0 +1,105 @@
    +Userspace LEDs
    +==============
    +
    +The uleds driver supports userspace LEDs. This can be useful for testing
    +triggers and can also be used to implement virtual LEDs.
    +
    +
    +Usage
    +=====
    +
    +When the driver is loaded, a character device is created at /dev/uleds. To
    +create a new LED class device, open /dev/uleds and write a uleds_user_dev
    +structure to it (found in kernel public header file linux/uleds.h).
    +
    + #define ULEDS_MAX_NAME_SIZE 80
    +
    + struct uleds_user_dev {
    + char name[ULEDS_MAX_NAME_SIZE];
    + };
    +
    +A new LED class device will be created with the name given. The name can be
    +any valid file name, but consider using the LED class naming convention of
    +"devicename:color:function".
    +
    +The current brightness is found by reading a single byte from the character
    +device. Values are unsigned: 0 to 255. Reading does not block and always returns
    +the most recent brightness value. The device node can also be polled to notify
    +when the brightness value changes.
    +
    +The LED class device will be removed when the open file handle to /dev/uleds
    +is closed.
    +
    +
    +Example
    +=======
    +
    +/*
    + * uledmon.c
    + *
    + * This program creates a new userspace LED class device and monitors it. A
    + * timestamp and brightness value is printed each time the brightness changes.
    + *
    + * Usage: uledmon <device-name>
    + *
    + * <device-name> is the name of the LED class device to be created. Pressing
    + * CTRL+C will exit.
    + */
    +
    +#include <fcntl.h>
    +#include <poll.h>
    +#include <stdio.h>
    +#include <string.h>
    +#include <time.h>
    +#include <unistd.h>
    +
    +#include <linux/uleds.h>
    +
    +int main(int argc, char const *argv[])
    +{
    + struct uleds_user_dev uleds_dev;
    + int fd, ret;
    + struct pollfd pfd;
    + unsigned char brightness;
    + struct timespec ts;
    +
    + if (argc != 2) {
    + fprintf(stderr, "Requires <device-name> argument\n");
    + return 1;
    + }
    +
    + strncpy(uleds_dev.name, argv[1], ULEDS_MAX_NAME_SIZE);
    +
    + fd = open("/dev/uleds", O_RDWR);
    + if (fd == -1) {
    + perror("Failed to open /dev/uleds");
    + return 1;
    + }
    +
    + ret = write(fd, &uleds_dev, sizeof(uleds_dev));
    + if (ret == -1) {
    + perror("Failed to write to /dev/uleds");
    + close(fd);
    + return 1;
    + }
    +
    + pfd.fd = fd;
    + pfd.events = POLLIN;
    + pfd.revents = 0;
    +
    + while (!(pfd.revents & (POLLERR | POLLHUP | POLLNVAL))) {
    + ret = read(fd, &brightness, 1);
    + if (ret == -1) {
    + perror("Failed to read from /dev/uleds");
    + close(fd);
    + return 1;
    + }
    + clock_gettime(CLOCK_MONOTONIC, &ts);
    + printf("[%ld.%09ld] %u\n", ts.tv_sec, ts.tv_nsec, brightness);
    + poll(&pfd, 1, -1);
    + }
    +
    + close(fd);
    +
    + return 0;
    +}
    diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
    index 7a628c6..5fd3f4c 100644
    --- a/drivers/leds/Kconfig
    +++ b/drivers/leds/Kconfig
    @@ -659,6 +659,14 @@ config LEDS_MLXCPLD
    This option enabled support for the LEDs on the Mellanox
    boards. Say Y to enabled these.

    +config LEDS_USER
    + tristate "Userspace LED support"
    + depends on LEDS_CLASS
    + help
    + This option enables support for userspace LEDs. Say 'y' to enable this
    + support in kernel. To compile this driver as a module, choose 'm' here:
    + the module will be called uleds.
    +
    comment "LED Triggers"
    source "drivers/leds/trigger/Kconfig"

    diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile
    index 3965070..d5331ff 100644
    --- a/drivers/leds/Makefile
    +++ b/drivers/leds/Makefile
    @@ -75,5 +75,8 @@ obj-$(CONFIG_LEDS_MLXCPLD) += leds-mlxcpld.o
    # LED SPI Drivers
    obj-$(CONFIG_LEDS_DAC124S085) += leds-dac124s085.o

    +# LED Userspace Drivers
    +obj-$(CONFIG_LEDS_USER) += uleds.o
    +
    # LED Triggers
    obj-$(CONFIG_LEDS_TRIGGERS) += trigger/
    diff --git a/drivers/leds/uleds.c b/drivers/leds/uleds.c
    new file mode 100644
    index 0000000..77a0bee
    --- /dev/null
    +++ b/drivers/leds/uleds.c
    @@ -0,0 +1,224 @@
    +/*
    + * Userspace driver for leds subsystem
    + *
    + * Copyright (C) 2016 David Lechner <david@lechnology.com>
    + *
    + * Based on uinput.c: Aristeu Sergio Rozanski Filho <aris@cathedrallabs.org>
    + *
    + * This program is free software; you can redistribute it and/or modify
    + * it under the terms of the GNU General Public License as published by
    + * the Free Software Foundation; either version 2 of the License, or
    + * (at your option) any later version.
    + *
    + * This program is distributed in the hope that it will be useful,
    + * but WITHOUT ANY WARRANTY; without even the implied warranty of
    + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    + * GNU General Public License for more details.
    + */
    +#include <linux/fs.h>
    +#include <linux/init.h>
    +#include <linux/leds.h>
    +#include <linux/miscdevice.h>
    +#include <linux/module.h>
    +#include <linux/poll.h>
    +#include <linux/sched.h>
    +#include <linux/slab.h>
    +
    +#include <uapi/linux/uleds.h>
    +
    +#define ULEDS_NAME "uleds"
    +
    +enum uleds_state {
    + ULEDS_STATE_UNKNOWN,
    + ULEDS_STATE_REGISTERED,
    +};
    +
    +struct uleds_device {
    + struct uleds_user_dev user_dev;
    + struct led_classdev led_cdev;
    + struct mutex mutex;
    + enum uleds_state state;
    + wait_queue_head_t waitq;
    + unsigned char brightness;
    + unsigned char new_data;
    +};
    +
    +static void uleds_brightness_set(struct led_classdev *led_cdev,
    + enum led_brightness brightness)
    +{
    + struct uleds_device *udev = container_of(led_cdev, struct uleds_device,
    + led_cdev);
    +
    + if (udev->brightness != brightness) {
    + udev->brightness = brightness;
    + udev->new_data = 1;
    + wake_up_interruptible(&udev->waitq);
    + }
    +}
    +
    +static int uleds_open(struct inode *inode, struct file *file)
    +{
    + struct uleds_device *udev;
    +
    + udev = kzalloc(sizeof(*udev), GFP_KERNEL);
    + if (!udev)
    + return -ENOMEM;
    +
    + udev->led_cdev.name = udev->user_dev.name;
    + udev->led_cdev.max_brightness = LED_FULL;
    + udev->led_cdev.brightness_set = uleds_brightness_set;
    +
    + mutex_init(&udev->mutex);
    + init_waitqueue_head(&udev->waitq);
    + udev->state = ULEDS_STATE_UNKNOWN;
    +
    + file->private_data = udev;
    + nonseekable_open(inode, file);
    +
    + return 0;
    +}
    +
    +static ssize_t uleds_write(struct file *file, const char __user *buffer,
    + size_t count, loff_t *ppos)
    +{
    + struct uleds_device *udev = file->private_data;
    + int ret;
    +
    + if (count == 0)
    + return 0;
    +
    + ret = mutex_lock_interruptible(&udev->mutex);
    + if (ret)
    + return ret;
    +
    + if (udev->state == ULEDS_STATE_REGISTERED) {
    + ret = -EBUSY;
    + goto out;
    + }
    +
    + if (count != sizeof(struct uleds_user_dev)) {
    + ret = -EINVAL;
    + goto out;
    + }
    +
    + if (copy_from_user(&udev->user_dev, buffer,
    + sizeof(struct uleds_user_dev))) {
    + ret = -EFAULT;
    + goto out;
    + }
    +
    + if (!udev->user_dev.name[0]) {
    + ret = -EINVAL;
    + goto out;
    + }
    +
    + ret = led_classdev_register(NULL, &udev->led_cdev);
    + if (ret < 0)
    + goto out;
    +
    + udev->state = ULEDS_STATE_REGISTERED;
    + ret = count;
    +
    +out:
    + mutex_unlock(&udev->mutex);
    +
    + return ret;
    +}
    +
    +static ssize_t uleds_read(struct file *file, char __user *buffer, size_t count,
    + loff_t *ppos)
    +{
    + struct uleds_device *udev = file->private_data;
    + ssize_t retval;
    +
    + if (count == 0)
    + return 0;
    +
    + if (count != 1)
    + return -EINVAL;
    +
    + do {
    + retval = mutex_lock_interruptible(&udev->mutex);
    + if (retval)
    + return retval;
    +
    + if (udev->state != ULEDS_STATE_REGISTERED) {
    + retval = -ENODEV;
    + } else if (!udev->new_data && (file->f_flags & O_NONBLOCK)) {
    + retval = -EAGAIN;
    + } else {
    + retval = copy_to_user(buffer, &udev->brightness, 1);
    + udev->new_data = 0;
    + retval = 1;
    + }
    +
    + mutex_unlock(&udev->mutex);
    +
    + if (retval || count == 0)
    + break;
    +
    + if (!(file->f_flags & O_NONBLOCK))
    + retval = wait_event_interruptible(udev->waitq,
    + udev->new_data ||
    + udev->state != ULEDS_STATE_REGISTERED);
    + } while (retval == 0);
    +
    + return retval;
    +}
    +
    +static unsigned int uleds_poll(struct file *file, poll_table *wait)
    +{
    + struct uleds_device *udev = file->private_data;
    +
    + poll_wait(file, &udev->waitq, wait);
    +
    + if (udev->new_data)
    + return POLLIN | POLLRDNORM;
    +
    + return 0;
    +}
    +
    +static int uleds_release(struct inode *inode, struct file *file)
    +{
    + struct uleds_device *udev = file->private_data;
    +
    + if (udev->state == ULEDS_STATE_REGISTERED) {
    + udev->state = ULEDS_STATE_UNKNOWN;
    + led_classdev_unregister(&udev->led_cdev);
    + }
    + kfree(udev);
    +
    + return 0;
    +}
    +
    +static const struct file_operations uleds_fops = {
    + .owner = THIS_MODULE,
    + .open = uleds_open,
    + .release = uleds_release,
    + .read = uleds_read,
    + .write = uleds_write,
    + .poll = uleds_poll,
    + .llseek = no_llseek,
    +};
    +
    +static struct miscdevice uleds_misc = {
    + .fops = &uleds_fops,
    + .minor = MISC_DYNAMIC_MINOR,
    + .name = ULEDS_NAME,
    +};
    +
    +static int __init uleds_init(void)
    +{
    + return misc_register(&uleds_misc);
    +}
    +module_init(uleds_init);
    +
    +static void __exit uleds_exit(void)
    +{
    + misc_deregister(&uleds_misc);
    +}
    +module_exit(uleds_exit);
    +
    +MODULE_AUTHOR("David Lechner <david@lechnology.com>");
    +MODULE_DESCRIPTION("Userspace driver for leds subsystem");
    +MODULE_LICENSE("GPL");
    diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
    index 185f8ea..416f5e6 100644
    --- a/include/uapi/linux/Kbuild
    +++ b/include/uapi/linux/Kbuild
    @@ -421,6 +421,7 @@ header-y += udp.h
    header-y += uhid.h
    header-y += uinput.h
    header-y += uio.h
    +header-y += uleds.h
    header-y += ultrasound.h
    header-y += un.h
    header-y += unistd.h
    diff --git a/include/uapi/linux/uleds.h b/include/uapi/linux/uleds.h
    new file mode 100644
    index 0000000..e78ed46
    --- /dev/null
    +++ b/include/uapi/linux/uleds.h
    @@ -0,0 +1,23 @@
    +/*
    + * Userspace driver support for leds subsystem
    + *
    + * This program is free software; you can redistribute it and/or modify
    + * it under the terms of the GNU General Public License as published by
    + * the Free Software Foundation; either version 2 of the License, or
    + * (at your option) any later version.
    + *
    + * This program is distributed in the hope that it will be useful,
    + * but WITHOUT ANY WARRANTY; without even the implied warranty of
    + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    + * GNU General Public License for more details.
    + */
    +#ifndef _UAPI__ULEDS_H_
    +#define _UAPI__ULEDS_H_
    +
    +#define ULEDS_MAX_NAME_SIZE 80
    +
    +struct uleds_user_dev {
    + char name[ULEDS_MAX_NAME_SIZE];
    +};
    +
    +#endif /* _UAPI__ULEDS_H_ */
    --
    2.7.4
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