// 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 = {
        .owner  = THIS_MODULE,
        .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[];
};

/* 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 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,
        .llseek = no_llseek,
        .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_simple_remove(&event_ida, minor);
        return error;
}

static int 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_simple_remove(&event_ida, MINOR(dev_data->dev.devt));
        hangup_device(dev_data);

        return 0;
}

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,
        },
        .owner = THIS_MODULE,
};

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");
MODULE_ALIAS("platform:" DRV_NAME);