// SPDX-License-Identifier: GPL-2.0
/*
 * Telemetry communication for Wilco EC
 *
 * Copyright 2019 Google LLC
 *
 * The Wilco Embedded Controller is able to send telemetry data
 * which is useful for enterprise applications. A daemon running on
 * the OS sends a command to the EC via a write() to a char device,
 * and can read the response with a read(). The write() request is
 * verified by the driver to ensure that it is performing only one
 * of the whitelisted commands, and that no extraneous data is
 * being transmitted to the EC. The response is passed directly
 * back to the reader with no modification.
 *
 * The character device will appear as /dev/wilco_telemN, where N
 * is some small non-negative integer, starting with 0. Only one
 * process may have the file descriptor open at a time. The calling
 * userspace program needs to keep the device file descriptor open
 * between the calls to write() and read() in order to preserve the
 * response. Up to 32 bytes will be available for reading.
 *
 * For testing purposes, try requesting the EC's firmware build
 * date, by sending the WILCO_EC_TELEM_GET_VERSION command with
 * argument index=3. i.e. write [0x38, 0x00, 0x03]
 * to the device node. An ASCII string of the build date is
 * returned.
 */

#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/module.h>
#include <linux/platform_data/wilco-ec.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/uaccess.h>

#define TELEM_DEV_NAME          "wilco_telem"
#define TELEM_CLASS_NAME        TELEM_DEV_NAME
#define DRV_NAME                TELEM_DEV_NAME
#define TELEM_DEV_NAME_FMT      (TELEM_DEV_NAME "%d")
static struct class telem_class = {
        .owner  = THIS_MODULE,
        .name   = TELEM_CLASS_NAME,
};

/* Keep track of all the device numbers used. */
#define TELEM_MAX_DEV 128
static int telem_major;
static DEFINE_IDA(telem_ida);

/* EC telemetry command codes */
#define WILCO_EC_TELEM_GET_LOG                  0x99
#define WILCO_EC_TELEM_GET_VERSION              0x38
#define WILCO_EC_TELEM_GET_FAN_INFO             0x2E
#define WILCO_EC_TELEM_GET_DIAG_INFO            0xFA
#define WILCO_EC_TELEM_GET_TEMP_INFO            0x95
#define WILCO_EC_TELEM_GET_TEMP_READ            0x2C
#define WILCO_EC_TELEM_GET_BATT_EXT_INFO        0x07

#define TELEM_ARGS_SIZE_MAX     30

/**
 * struct wilco_ec_telem_request - Telemetry command and arguments sent to EC.
 * @command: One of WILCO_EC_TELEM_GET_* command codes.
 * @reserved: Must be 0.
 * @args: The first N bytes are one of telem_args_get_* structs, the rest is 0.
 */
struct wilco_ec_telem_request {
        u8 command;
        u8 reserved;
        u8 args[TELEM_ARGS_SIZE_MAX];
} __packed;

/*
 * The following telem_args_get_* structs are embedded within the |args| field
 * of wilco_ec_telem_request.
 */

struct telem_args_get_log {
        u8 log_type;
        u8 log_index;
} __packed;

/*
 * Get a piece of info about the EC firmware version:
 * 0 = label
 * 1 = svn_rev
 * 2 = model_no
 * 3 = build_date
 * 4 = frio_version
 */
struct telem_args_get_version {
        u8 index;
} __packed;

struct telem_args_get_fan_info {
        u8 command;
        u8 fan_number;
        u8 arg;
} __packed;

struct telem_args_get_diag_info {
        u8 type;
        u8 sub_type;
} __packed;

struct telem_args_get_temp_info {
        u8 command;
        u8 index;
        u8 field;
        u8 zone;
} __packed;

struct telem_args_get_temp_read {
        u8 sensor_index;
} __packed;

struct telem_args_get_batt_ext_info {
        u8 var_args[5];
} __packed;

/**
 * check_telem_request() - Ensure that a request from userspace is valid.
 * @rq: Request buffer copied from userspace.
 * @size: Number of bytes copied from userspace.
 *
 * Return: 0 if valid, -EINVAL if bad command or reserved byte is non-zero,
 *         -EMSGSIZE if the request is too long.
 *
 * We do not want to allow userspace to send arbitrary telemetry commands to
 * the EC. Therefore we check to ensure that
 * 1. The request follows the format of struct wilco_ec_telem_request.
 * 2. The supplied command code is one of the whitelisted commands.
 * 3. The request only contains the necessary data for the header and arguments.
 */
static int check_telem_request(struct wilco_ec_telem_request *rq,
                               size_t size)
{
        size_t max_size = offsetof(struct wilco_ec_telem_request, args);

        if (rq->reserved)
                return -EINVAL;

        switch (rq->command) {
        case WILCO_EC_TELEM_GET_LOG:
                max_size += sizeof(struct telem_args_get_log);
                break;
        case WILCO_EC_TELEM_GET_VERSION:
                max_size += sizeof(struct telem_args_get_version);
                break;
        case WILCO_EC_TELEM_GET_FAN_INFO:
                max_size += sizeof(struct telem_args_get_fan_info);
                break;
        case WILCO_EC_TELEM_GET_DIAG_INFO:
                max_size += sizeof(struct telem_args_get_diag_info);
                break;
        case WILCO_EC_TELEM_GET_TEMP_INFO:
                max_size += sizeof(struct telem_args_get_temp_info);
                break;
        case WILCO_EC_TELEM_GET_TEMP_READ:
                max_size += sizeof(struct telem_args_get_temp_read);
                break;
        case WILCO_EC_TELEM_GET_BATT_EXT_INFO:
                max_size += sizeof(struct telem_args_get_batt_ext_info);
                break;
        default:
                return -EINVAL;
        }

        return (size <= max_size) ? 0 : -EMSGSIZE;
}

/**
 * struct telem_device_data - Data for a Wilco EC device that queries telemetry.
 * @cdev: Char dev that userspace reads and polls from.
 * @dev: Device associated with the %cdev.
 * @ec: Wilco EC that we will be communicating with using the mailbox interface.
 * @available: Boolean of if the device can be opened.
 */
struct telem_device_data {
        struct device dev;
        struct cdev cdev;
        struct wilco_ec_device *ec;
        atomic_t available;
};

#define TELEM_RESPONSE_SIZE     EC_MAILBOX_DATA_SIZE

/**
 * struct telem_session_data - Data that exists between open() and release().
 * @dev_data: Pointer to get back to the device data and EC.
 * @request: Command and arguments sent to EC.
 * @response: Response buffer of data from EC.
 * @has_msg: Is there data available to read from a previous write?
 */
struct telem_session_data {
        struct telem_device_data *dev_data;
        struct wilco_ec_telem_request request;
        u8 response[TELEM_RESPONSE_SIZE];
        bool has_msg;
};

/**
 * telem_open() - Callback for when the device node is opened.
 * @inode: inode for this char device node.
 * @filp: file for this char device node.
 *
 * We need to ensure that after writing a command to the device,
 * the same userspace process reads the corresponding result.
 * Therefore, we increment a refcount on opening the device, so that
 * only one process can communicate with the EC at a time.
 *
 * Return: 0 on success, or negative error code on failure.
 */
static int telem_open(struct inode *inode, struct file *filp)
{
        struct telem_device_data *dev_data;
        struct telem_session_data *sess_data;

        /* Ensure device isn't already open */
        dev_data = container_of(inode->i_cdev, struct telem_device_data, cdev);
        if (atomic_cmpxchg(&dev_data->available, 1, 0) == 0)
                return -EBUSY;

        get_device(&dev_data->dev);

        sess_data = kzalloc(sizeof(*sess_data), GFP_KERNEL);
        if (!sess_data) {
                atomic_set(&dev_data->available, 1);
                return -ENOMEM;
        }
        sess_data->dev_data = dev_data;
        sess_data->has_msg = false;

        nonseekable_open(inode, filp);
        filp->private_data = sess_data;

        return 0;
}

static ssize_t telem_write(struct file *filp, const char __user *buf,
                           size_t count, loff_t *pos)
{
        struct telem_session_data *sess_data = filp->private_data;
        struct wilco_ec_message msg = {};
        int ret;

        if (count > sizeof(sess_data->request))
                return -EMSGSIZE;
        if (copy_from_user(&sess_data->request, buf, count))
                return -EFAULT;
        ret = check_telem_request(&sess_data->request, count);
        if (ret < 0)
                return ret;

        memset(sess_data->response, 0, sizeof(sess_data->response));
        msg.type = WILCO_EC_MSG_TELEMETRY;
        msg.request_data = &sess_data->request;
        msg.request_size = sizeof(sess_data->request);
        msg.response_data = sess_data->response;
        msg.response_size = sizeof(sess_data->response);

        ret = wilco_ec_mailbox(sess_data->dev_data->ec, &msg);
        if (ret < 0)
                return ret;
        if (ret != sizeof(sess_data->response))
                return -EMSGSIZE;

        sess_data->has_msg = true;

        return count;
}

static ssize_t telem_read(struct file *filp, char __user *buf, size_t count,
                          loff_t *pos)
{
        struct telem_session_data *sess_data = filp->private_data;

        if (!sess_data->has_msg)
                return -ENODATA;
        if (count > sizeof(sess_data->response))
                return -EINVAL;

        if (copy_to_user(buf, sess_data->response, count))
                return -EFAULT;

        sess_data->has_msg = false;

        return count;
}

static int telem_release(struct inode *inode, struct file *filp)
{
        struct telem_session_data *sess_data = filp->private_data;

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

        return 0;
}

static const struct file_operations telem_fops = {
        .open = telem_open,
        .write = telem_write,
        .read = telem_read,
        .release = telem_release,
        .llseek = no_llseek,
        .owner = THIS_MODULE,
};

/**
 * telem_device_free() - Callback to free the telem_device_data structure.
 * @d: The device embedded in our device data, which we have been ref counting.
 *
 * Once all open file descriptors are closed and the device has been removed,
 * the refcount of the device will fall to 0 and this will be called.
 */
static void telem_device_free(struct device *d)
{
        struct telem_device_data *dev_data;

        dev_data = container_of(d, struct telem_device_data, dev);
        kfree(dev_data);
}

/**
 * telem_device_probe() - Callback when creating a new device.
 * @pdev: platform device that we will be receiving telems 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.
 *
 * Return: 0 on success, negative error code on failure.
 */
static int telem_device_probe(struct platform_device *pdev)
{
        struct telem_device_data *dev_data;
        int error, minor;

        /* Get the next available device number */
        minor = ida_alloc_max(&telem_ida, TELEM_MAX_DEV-1, GFP_KERNEL);
        if (minor < 0) {
                error = minor;
                dev_err(&pdev->dev, "Failed to find minor number: %d", error);
                return error;
        }

        dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
        if (!dev_data) {
                ida_simple_remove(&telem_ida, minor);
                return -ENOMEM;
        }

        /* Initialize the device data */
        dev_data->ec = dev_get_platdata(&pdev->dev);
        atomic_set(&dev_data->available, 1);
        platform_set_drvdata(pdev, dev_data);

        /* Initialize the device */
        dev_data->dev.devt = MKDEV(telem_major, minor);
        dev_data->dev.class = &telem_class;
        dev_data->dev.release = telem_device_free;
        dev_set_name(&dev_data->dev, TELEM_DEV_NAME_FMT, minor);
        device_initialize(&dev_data->dev);

        /* Initialize the character device and add it to userspace */;
        cdev_init(&dev_data->cdev, &telem_fops);
        error = cdev_device_add(&dev_data->cdev, &dev_data->dev);
        if (error) {
                put_device(&dev_data->dev);
                ida_simple_remove(&telem_ida, minor);
                return error;
        }

        return 0;
}

static int telem_device_remove(struct platform_device *pdev)
{
        struct telem_device_data *dev_data = platform_get_drvdata(pdev);

        cdev_device_del(&dev_data->cdev, &dev_data->dev);
        put_device(&dev_data->dev);
        ida_simple_remove(&telem_ida, MINOR(dev_data->dev.devt));

        return 0;
}

static struct platform_driver telem_driver = {
        .probe = telem_device_probe,
        .remove = telem_device_remove,
        .driver = {
                .name = DRV_NAME,
        },
};

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

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

        /* Request the kernel for device numbers, starting with minor=0 */
        ret = alloc_chrdev_region(&dev_num, 0, TELEM_MAX_DEV, TELEM_DEV_NAME);
        if (ret) {
                pr_err(DRV_NAME ": Failed allocating dev numbers: %d", ret);
                goto destroy_class;
        }
        telem_major = MAJOR(dev_num);

        ret = platform_driver_register(&telem_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(telem_major, 0), TELEM_MAX_DEV);
destroy_class:
        class_unregister(&telem_class);
        ida_destroy(&telem_ida);
        return ret;
}

static void __exit telem_module_exit(void)
{
        platform_driver_unregister(&telem_driver);
        unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
        class_unregister(&telem_class);
        ida_destroy(&telem_ida);
}

module_init(telem_module_init);
module_exit(telem_module_exit);

MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
MODULE_DESCRIPTION("Wilco EC telemetry driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:" DRV_NAME);