leds: Introduce userspace LED class driver

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 LED 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>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>

3 files changed, 246 insertions, 0 deletions

diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index 7a628c6516f6..5fd3f4ca0c3c 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 3965070190f5..d5331ff5b563 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 000000000000..5e9e8a1fdefb
--- /dev/null
+++ b/drivers/leds/uleds.c
@@ -0,0 +1,235 @@
+/*
+ * Userspace driver for the LED 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;
+        int                     brightness;
+        bool                    new_data;
+};
+
+static struct miscdevice uleds_misc;
+
+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 = true;
+                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.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;
+        const char *name;
+        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;
+        }
+
+        name = udev->user_dev.name;
+        if (!name[0] || !strcmp(name, ".") || !strcmp(name, "..") ||
+            strchr(name, '/')) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        if (udev->user_dev.max_brightness <= 0) {
+                ret = -EINVAL;
+                goto out;
+        }
+        udev->led_cdev.max_brightness = udev->user_dev.max_brightness;
+
+        ret = devm_led_classdev_register(uleds_misc.this_device,
+                                         &udev->led_cdev);
+        if (ret < 0)
+                goto out;
+
+        udev->new_data = true;
+        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 < sizeof(udev->brightness))
+                return 0;
+
+        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 if (udev->new_data) {
+                        retval = copy_to_user(buffer, &udev->brightness,
+                                              sizeof(udev->brightness));
+                        udev->new_data = false;
+                        retval = sizeof(udev->brightness);
+                }
+
+                mutex_unlock(&udev->mutex);
+
+                if (retval)
+                        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;
+                devm_led_classdev_unregister(uleds_misc.this_device,
+                                             &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 the LED subsystem");
+MODULE_LICENSE("GPL");