// SPDX-License-Identifier: GPL-2.0
/*
 * ACPI event handling for Wilco Embedded Controller
 *
 * Copyright 2019 Google LLC
 *
 * The Wilco Embedded Controller can create custom events that
 * are not handled as standard ACPI objects. These events can
 * contain information about changes in EC controlled features,
 * such as errors and events in the dock or display. For example,
 * an event is triggered if the dock is plugged into a display
 * incorrectly. These events are needed for telemetry and
 * diagnostics reasons, and for possibly alerting the user.

 * These events are triggered by the EC with an ACPI Notify(0x90),
 * and then the BIOS reads the event buffer from EC RAM via an
 * ACPI method. When the OS receives these events via ACPI,
 * it passes them along to this driver. The events are put into
 * a queue which can be read by a userspace daemon via a char device
 * that implements read() and poll(). The event queue acts as a
 * circular buffer of size 64, so if there are no userspace consumers
 * the kernel will not run out of memory. The char device will appear at
 * /dev/wilco_event{n}, where n is some small non-negative integer,
 * starting from 0. Standard ACPI events such as the battery getting
 * plugged/unplugged can also come through this path, but they are
 * dealt with via other paths, and are ignored here.

 * To test, you can tail the binary data with
 * $ cat /dev/wilco_event0 | hexdump -ve '1/1 "%x\n"'
 * and then create an event by plugging/unplugging the battery.
 */

#include <linux/acpi.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/idr.h>
#include <linux/io.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/poll.h>
#include <linux/spinlock.h>
#include <linux/uaccess.h>
#include <linux/wait.h>

/* ACPI Notify event code indicating event data is available. */
#define EC_ACPI_NOTIFY_EVENT		0x90
/* ACPI Method to execute to retrieve event data buffer from the EC. */
#define EC_ACPI_GET_EVENT		"QSET"
/* Maximum number of words in event data returned by the EC. */
#define EC_ACPI_MAX_EVENT_WORDS		6
#define EC_ACPI_MAX_EVENT_SIZE \
	(sizeof(struct ec_event) + (EC_ACPI_MAX_EVENT_WORDS) * sizeof(u16))

/* Node will appear in /dev/EVENT_DEV_NAME */
#define EVENT_DEV_NAME		"wilco_event"
#define EVENT_CLASS_NAME	EVENT_DEV_NAME
#define DRV_NAME		EVENT_DEV_NAME
#define EVENT_DEV_NAME_FMT	(EVENT_DEV_NAME "%d")
static struct class event_class = {
	.name	= EVENT_CLASS_NAME,
};

/* Keep track of all the device numbers used. */
#define EVENT_MAX_DEV 128
static int event_major;
static DEFINE_IDA(event_ida);

/* Size of circular queue of events. */
#define MAX_NUM_EVENTS 64

/**
 * struct ec_event - Extended event returned by the EC.
 * @size: Number of 16bit words in structure after the size word.
 * @type: Extended event type, meaningless for us.
 * @event: Event data words.  Max count is %EC_ACPI_MAX_EVENT_WORDS.
 */
struct ec_event {
	u16 size;
	u16 type;
	u16 event[];
} __packed;

#define ec_event_num_words(ev) (ev->size - 1)
#define ec_event_size(ev) (sizeof(*ev) + (ec_event_num_words(ev) * sizeof(u16)))

/**
 * struct ec_event_queue - Circular queue for events.
 * @capacity: Number of elements the queue can hold.
 * @head: Next index to write to.
 * @tail: Next index to read from.
 * @entries: Array of events.
 */
struct ec_event_queue {
	int capacity;
	int head;
	int tail;
	struct ec_event *entries[] __counted_by(capacity);
};

/* Maximum number of events to store in ec_event_queue */
static int queue_size = 64;
module_param(queue_size, int, 0644);

static struct ec_event_queue *event_queue_new(int capacity)
{
	struct ec_event_queue *q;

	q = kzalloc(struct_size(q, entries, capacity), GFP_KERNEL);
	if (!q)
		return NULL;

	q->capacity = capacity;

	return q;
}

static inline bool event_queue_empty(struct ec_event_queue *q)
{
	/* head==tail when both full and empty, but head==NULL when empty */
	return q->head == q->tail && !q->entries[q->head];
}

static inline bool event_queue_full(struct ec_event_queue *q)
{
	/* head==tail when both full and empty, but head!=NULL when full */
	return q->head == q->tail && q->entries[q->head];
}

static struct ec_event *event_queue_pop(struct ec_event_queue *q)
{
	struct ec_event *ev;

	if (event_queue_empty(q))
		return NULL;

	ev = q->entries[q->tail];
	q->entries[q->tail] = NULL;
	q->tail = (q->tail + 1) % q->capacity;

	return ev;
}

/*
 * If full, overwrite the oldest event and return it so the caller
 * can kfree it. If not full, return NULL.
 */
static struct ec_event *event_queue_push(struct ec_event_queue *q,
					 struct ec_event *ev)
{
	struct ec_event *popped = NULL;

	if (event_queue_full(q))
		popped = event_queue_pop(q);
	q->entries[q->head] = ev;
	q->head = (q->head + 1) % q->capacity;

	return popped;
}

static void event_queue_free(struct ec_event_queue *q)
{
	struct ec_event *event;

	while ((event = event_queue_pop(q)) != NULL)
		kfree(event);

	kfree(q);
}

/**
 * struct event_device_data - Data for a Wilco EC device that responds to ACPI.
 * @events: Circular queue of EC events to be provided to userspace.
 * @queue_lock: Protect the queue from simultaneous read/writes.
 * @wq: Wait queue to notify processes when events are available or the
 *	device has been removed.
 * @cdev: Char dev that userspace reads() and polls() from.
 * @dev: Device associated with the %cdev.
 * @exist: Has the device been not been removed? Once a device has been removed,
 *	   writes, reads, and new opens will fail.
 * @available: Guarantee only one client can open() file and read from queue.
 *
 * There will be one of these structs for each ACPI device registered. This data
 * is the queue of events received from ACPI that still need to be read from
 * userspace, the device and char device that userspace is using, a wait queue
 * used to notify different threads when something has changed, plus a flag
 * on whether the ACPI device has been removed.
 */
struct event_device_data {
	struct ec_event_queue *events;
	spinlock_t queue_lock;
	wait_queue_head_t wq;
	struct device dev;
	struct cdev cdev;
	bool exist;
	atomic_t available;
};

/**
 * enqueue_events() - Place EC events in queue to be read by userspace.
 * @adev: Device the events came from.
 * @buf: Buffer of event data.
 * @length: Length of event data buffer.
 *
 * %buf contains a number of ec_event's, packed one after the other.
 * Each ec_event is of variable length. Start with the first event, copy it
 * into a persistent ec_event, store that entry in the queue, move on
 * to the next ec_event in buf, and repeat.
 *
 * Return: 0 on success or negative error code on failure.
 */
static int enqueue_events(struct acpi_device *adev, const u8 *buf, u32 length)
{
	struct event_device_data *dev_data = adev->driver_data;
	struct ec_event *event, *queue_event, *old_event;
	size_t num_words, event_size;
	u32 offset = 0;

	while (offset < length) {
		event = (struct ec_event *)(buf + offset);

		num_words = ec_event_num_words(event);
		event_size = ec_event_size(event);
		if (num_words > EC_ACPI_MAX_EVENT_WORDS) {
			dev_err(&adev->dev, "Too many event words: %zu > %d\n",
				num_words, EC_ACPI_MAX_EVENT_WORDS);
			return -EOVERFLOW;
		}

		/* Ensure event does not overflow the available buffer */
		if ((offset + event_size) > length) {
			dev_err(&adev->dev, "Event exceeds buffer: %zu > %d\n",
				offset + event_size, length);
			return -EOVERFLOW;
		}

		/* Point to the next event in the buffer */
		offset += event_size;

		/* Copy event into the queue */
		queue_event = kmemdup(event, event_size, GFP_KERNEL);
		if (!queue_event)
			return -ENOMEM;
		spin_lock(&dev_data->queue_lock);
		old_event = event_queue_push(dev_data->events, queue_event);
		spin_unlock(&dev_data->queue_lock);
		kfree(old_event);
		wake_up_interruptible(&dev_data->wq);
	}

	return 0;
}

/**
 * event_device_notify() - Callback when EC generates an event over ACPI.
 * @adev: The device that the event is coming from.
 * @value: Value passed to Notify() in ACPI.
 *
 * This function will read the events from the device and enqueue them.
 */
static void event_device_notify(struct acpi_device *adev, u32 value)
{
	struct acpi_buffer event_buffer = { ACPI_ALLOCATE_BUFFER, NULL };
	union acpi_object *obj;
	acpi_status status;

	if (value != EC_ACPI_NOTIFY_EVENT) {
		dev_err(&adev->dev, "Invalid event: 0x%08x\n", value);
		return;
	}

	/* Execute ACPI method to get event data buffer. */
	status = acpi_evaluate_object(adev->handle, EC_ACPI_GET_EVENT,
				      NULL, &event_buffer);
	if (ACPI_FAILURE(status)) {
		dev_err(&adev->dev, "Error executing ACPI method %s()\n",
			EC_ACPI_GET_EVENT);
		return;
	}

	obj = (union acpi_object *)event_buffer.pointer;
	if (!obj) {
		dev_err(&adev->dev, "Nothing returned from %s()\n",
			EC_ACPI_GET_EVENT);
		return;
	}
	if (obj->type != ACPI_TYPE_BUFFER) {
		dev_err(&adev->dev, "Invalid object returned from %s()\n",
			EC_ACPI_GET_EVENT);
		kfree(obj);
		return;
	}
	if (obj->buffer.length < sizeof(struct ec_event)) {
		dev_err(&adev->dev, "Invalid buffer length %d from %s()\n",
			obj->buffer.length, EC_ACPI_GET_EVENT);
		kfree(obj);
		return;
	}

	enqueue_events(adev, obj->buffer.pointer, obj->buffer.length);
	kfree(obj);
}

static int event_open(struct inode *inode, struct file *filp)
{
	struct event_device_data *dev_data;

	dev_data = container_of(inode->i_cdev, struct event_device_data, cdev);
	if (!dev_data->exist)
		return -ENODEV;

	if (atomic_cmpxchg(&dev_data->available, 1, 0) == 0)
		return -EBUSY;

	/* Increase refcount on device so dev_data is not freed */
	get_device(&dev_data->dev);
	stream_open(inode, filp);
	filp->private_data = dev_data;

	return 0;
}

static __poll_t event_poll(struct file *filp, poll_table *wait)
{
	struct event_device_data *dev_data = filp->private_data;
	__poll_t mask = 0;

	poll_wait(filp, &dev_data->wq, wait);
	if (!dev_data->exist)
		return EPOLLHUP;
	if (!event_queue_empty(dev_data->events))
		mask |= EPOLLIN | EPOLLRDNORM | EPOLLPRI;
	return mask;
}

/**
 * event_read() - Callback for passing event data to userspace via read().
 * @filp: The file we are reading from.
 * @buf: Pointer to userspace buffer to fill with one event.
 * @count: Number of bytes requested. Must be at least EC_ACPI_MAX_EVENT_SIZE.
 * @pos: File position pointer, irrelevant since we don't support seeking.
 *
 * Removes the first event from the queue, places it in the passed buffer.
 *
 * If there are no events in the queue, then one of two things happens,
 * depending on if the file was opened in nonblocking mode: If in nonblocking
 * mode, then return -EAGAIN to say there's no data. If in blocking mode, then
 * block until an event is available.
 *
 * Return: Number of bytes placed in buffer, negative error code on failure.
 */
static ssize_t event_read(struct file *filp, char __user *buf, size_t count,
			  loff_t *pos)
{
	struct event_device_data *dev_data = filp->private_data;
	struct ec_event *event;
	ssize_t n_bytes_written = 0;
	int err;

	/* We only will give them the entire event at once */
	if (count != 0 && count < EC_ACPI_MAX_EVENT_SIZE)
		return -EINVAL;

	spin_lock(&dev_data->queue_lock);
	while (event_queue_empty(dev_data->events)) {
		spin_unlock(&dev_data->queue_lock);
		if (filp->f_flags & O_NONBLOCK)
			return -EAGAIN;

		err = wait_event_interruptible(dev_data->wq,
					!event_queue_empty(dev_data->events) ||
					!dev_data->exist);
		if (err)
			return err;

		/* Device was removed as we waited? */
		if (!dev_data->exist)
			return -ENODEV;
		spin_lock(&dev_data->queue_lock);
	}
	event = event_queue_pop(dev_data->events);
	spin_unlock(&dev_data->queue_lock);
	n_bytes_written = ec_event_size(event);
	if (copy_to_user(buf, event, n_bytes_written))
		n_bytes_written = -EFAULT;
	kfree(event);

	return n_bytes_written;
}

static int event_release(struct inode *inode, struct file *filp)
{
	struct event_device_data *dev_data = filp->private_data;

	atomic_set(&dev_data->available, 1);
	put_device(&dev_data->dev);

	return 0;
}

static const struct file_operations event_fops = {
	.open = event_open,
	.poll  = event_poll,
	.read = event_read,
	.release = event_release,
	.owner = THIS_MODULE,
};

/**
 * free_device_data() - Callback to free the event_device_data structure.
 * @d: The device embedded in our device data, which we have been ref counting.
 *
 * This is called only after event_device_remove() has been called and all
 * userspace programs have called event_release() on all the open file
 * descriptors.
 */
static void free_device_data(struct device *d)
{
	struct event_device_data *dev_data;

	dev_data = container_of(d, struct event_device_data, dev);
	event_queue_free(dev_data->events);
	kfree(dev_data);
}

static void hangup_device(struct event_device_data *dev_data)
{
	dev_data->exist = false;
	/* Wake up the waiting processes so they can close. */
	wake_up_interruptible(&dev_data->wq);
	put_device(&dev_data->dev);
}

/**
 * event_device_add() - Callback when creating a new device.
 * @adev: ACPI device that we will be receiving events from.
 *
 * This finds a free minor number for the device, allocates and initializes
 * some device data, and creates a new device and char dev node.
 *
 * The device data is freed in free_device_data(), which is called when
 * %dev_data->dev is release()ed. This happens after all references to
 * %dev_data->dev are dropped, which happens once both event_device_remove()
 * has been called and every open()ed file descriptor has been release()ed.
 *
 * Return: 0 on success, negative error code on failure.
 */
static int event_device_add(struct acpi_device *adev)
{
	struct event_device_data *dev_data;
	int error, minor;

	minor = ida_alloc_max(&event_ida, EVENT_MAX_DEV-1, GFP_KERNEL);
	if (minor < 0) {
		error = minor;
		dev_err(&adev->dev, "Failed to find minor number: %d\n", error);
		return error;
	}

	dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
	if (!dev_data) {
		error = -ENOMEM;
		goto free_minor;
	}

	/* Initialize the device data. */
	adev->driver_data = dev_data;
	dev_data->events = event_queue_new(queue_size);
	if (!dev_data->events) {
		kfree(dev_data);
		error = -ENOMEM;
		goto free_minor;
	}
	spin_lock_init(&dev_data->queue_lock);
	init_waitqueue_head(&dev_data->wq);
	dev_data->exist = true;
	atomic_set(&dev_data->available, 1);

	/* Initialize the device. */
	dev_data->dev.devt = MKDEV(event_major, minor);
	dev_data->dev.class = &event_class;
	dev_data->dev.release = free_device_data;
	dev_set_name(&dev_data->dev, EVENT_DEV_NAME_FMT, minor);
	device_initialize(&dev_data->dev);

	/* Initialize the character device, and add it to userspace. */
	cdev_init(&dev_data->cdev, &event_fops);
	error = cdev_device_add(&dev_data->cdev, &dev_data->dev);
	if (error)
		goto free_dev_data;

	return 0;

free_dev_data:
	hangup_device(dev_data);
free_minor:
	ida_free(&event_ida, minor);
	return error;
}

static void event_device_remove(struct acpi_device *adev)
{
	struct event_device_data *dev_data = adev->driver_data;

	cdev_device_del(&dev_data->cdev, &dev_data->dev);
	ida_free(&event_ida, MINOR(dev_data->dev.devt));
	hangup_device(dev_data);
}

static const struct acpi_device_id event_acpi_ids[] = {
	{ "GOOG000D", 0 },
	{ }
};
MODULE_DEVICE_TABLE(acpi, event_acpi_ids);

static struct acpi_driver event_driver = {
	.name = DRV_NAME,
	.class = DRV_NAME,
	.ids = event_acpi_ids,
	.ops = {
		.add = event_device_add,
		.notify = event_device_notify,
		.remove = event_device_remove,
	},
};

static int __init event_module_init(void)
{
	dev_t dev_num = 0;
	int ret;

	ret = class_register(&event_class);
	if (ret) {
		pr_err(DRV_NAME ": Failed registering class: %d\n", ret);
		return ret;
	}

	/* Request device numbers, starting with minor=0. Save the major num. */
	ret = alloc_chrdev_region(&dev_num, 0, EVENT_MAX_DEV, EVENT_DEV_NAME);
	if (ret) {
		pr_err(DRV_NAME ": Failed allocating dev numbers: %d\n", ret);
		goto destroy_class;
	}
	event_major = MAJOR(dev_num);

	ret = acpi_bus_register_driver(&event_driver);
	if (ret < 0) {
		pr_err(DRV_NAME ": Failed registering driver: %d\n", ret);
		goto unregister_region;
	}

	return 0;

unregister_region:
	unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);
destroy_class:
	class_unregister(&event_class);
	ida_destroy(&event_ida);
	return ret;
}

static void __exit event_module_exit(void)
{
	acpi_bus_unregister_driver(&event_driver);
	unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);
	class_unregister(&event_class);
	ida_destroy(&event_ida);
}

module_init(event_module_init);
module_exit(event_module_exit);

MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
MODULE_DESCRIPTION("Wilco EC ACPI event driver");
MODULE_LICENSE("GPL");