Subject: Re: [PATCH v4 1/3] leds: Introduce userspace leds driver
To: David Lechner <david@lechnology.com>,
        Richard Purdie <rpurdie@rpsys.net>
Cc: linux-kernel@vger.kernel.org, linux-leds@vger.kernel.org,
        Marcel Holtmann <marcel@holtmann.org>, Pavel Machek <pavel@ucw.cz>
From: Jacek Anaszewski <j.anaszewski@samsung.com>
Message-id: <0bfdfd46-35e5-321c-5759-0cc96be862fd@samsung.com>
Date: Tue, 08 Nov 2016 12:26:04 +0100
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Hi David,

On 09/16/2016 09:16 PM, David Lechner wrote:
> 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>
> ---
>  Documentation/leds/uleds.txt |  36 +++++++
>  drivers/leds/Kconfig         |   8 ++
>  drivers/leds/Makefile        |   3 +
>  drivers/leds/uleds.c         | 230 +++++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/Kbuild    |   1 +
>  include/uapi/linux/uleds.h   |  23 +++++
>  6 files changed, 301 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..486d473
> --- /dev/null
> +++ b/Documentation/leds/uleds.txt
> @@ -0,0 +1,36 @@
> +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 LEDS_MAX_NAME_SIZE 64
> +
> +    struct uleds_user_dev {
> +        char name[LEDS_MAX_NAME_SIZE];
> +    };
> +
> +A new LED class device will be created with the name given. The name can be
> +any valid sysfs device node 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 will block until the brightness
> +changes. 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.
> +
> +Multiple LED class devices are created by opening additional file handles to
> +/dev/uleds.
> +
> +See tools/leds/uledmon.c for an example userspace program.
> 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..59ea23e
> --- /dev/null
> +++ b/drivers/leds/uleds.c
> @@ -0,0 +1,229 @@
> +/*
> + * 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;

I've just noticed that this is wrong, since LED subsystem
brightness type is enum led_brightness, i.e. int.
LED_FULL (255) value is a legacy enum value that can be overridden
by max_brightness property.

Please submit a fix so that I could merge it with the original
patch before sending it upstream.

Thanks,
Jacek Anaszewski


> +	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.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;
> +	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;
> +	}
> +
> +	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 == 0)
> +		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, 1);
> +			udev->new_data = false;
> +			retval = 1;
> +		}
> +
> +		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 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..6f277f3
> --- /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 LEDS_MAX_NAME_SIZE	64
> +
> +struct uleds_user_dev {
> +	char name[LEDS_MAX_NAME_SIZE];
> +};
> +
> +#endif /* _UAPI__ULEDS_H_ */
>