alistair23-linux/drivers/platform/x86/intel_speed_select_if/isst_if_common.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Intel Speed Select Interface: Common functions
 * Copyright (c) 2019, Intel Corporation.
 * All rights reserved.
 *
 * Author: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
 */

#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/uaccess.h>
#include <uapi/linux/isst_if.h>

#include "isst_if_common.h"

static struct isst_if_cmd_cb punit_callbacks[ISST_IF_DEV_MAX];

static int isst_if_get_platform_info(void __user *argp)
{
	struct isst_if_platform_info info;

	info.api_version = ISST_IF_API_VERSION,
	info.driver_version = ISST_IF_DRIVER_VERSION,
	info.max_cmds_per_ioctl = ISST_IF_CMD_LIMIT,
	info.mbox_supported = punit_callbacks[ISST_IF_DEV_MBOX].registered;
	info.mmio_supported = punit_callbacks[ISST_IF_DEV_MMIO].registered;

	if (copy_to_user(argp, &info, sizeof(info)))
		return -EFAULT;

	return 0;
}

static long isst_if_def_ioctl(struct file *file, unsigned int cmd,
			      unsigned long arg)
{
	void __user *argp = (void __user *)arg;
	long ret = -ENOTTY;

	switch (cmd) {
	case ISST_IF_GET_PLATFORM_INFO:
		ret = isst_if_get_platform_info(argp);
		break;
	default:
		break;
	}

	return ret;
}

static DEFINE_MUTEX(punit_misc_dev_lock);
static int misc_usage_count;
static int misc_device_ret;
static int misc_device_open;

static int isst_if_open(struct inode *inode, struct file *file)
{
	int i, ret = 0;

	/* Fail open, if a module is going away */
	mutex_lock(&punit_misc_dev_lock);
	for (i = 0; i < ISST_IF_DEV_MAX; ++i) {
		struct isst_if_cmd_cb *cb = &punit_callbacks[i];

		if (cb->registered && !try_module_get(cb->owner)) {
			ret = -ENODEV;
			break;
		}
	}
	if (ret) {
		int j;

		for (j = 0; j < i; ++j) {
			struct isst_if_cmd_cb *cb;

			cb = &punit_callbacks[j];
			if (cb->registered)
				module_put(cb->owner);
		}
	} else {
		misc_device_open++;
	}
	mutex_unlock(&punit_misc_dev_lock);

	return ret;
}

static int isst_if_relase(struct inode *inode, struct file *f)
{
	int i;

	mutex_lock(&punit_misc_dev_lock);
	misc_device_open--;
	for (i = 0; i < ISST_IF_DEV_MAX; ++i) {
		struct isst_if_cmd_cb *cb = &punit_callbacks[i];

		if (cb->registered)
			module_put(cb->owner);
	}
	mutex_unlock(&punit_misc_dev_lock);

	return 0;
}

static const struct file_operations isst_if_char_driver_ops = {
	.open = isst_if_open,
	.unlocked_ioctl = isst_if_def_ioctl,
	.release = isst_if_relase,
};

static struct miscdevice isst_if_char_driver = {
	.minor		= MISC_DYNAMIC_MINOR,
	.name		= "isst_interface",
	.fops		= &isst_if_char_driver_ops,
};

/**
 * isst_if_cdev_register() - Register callback for IOCTL
 * @device_type: The device type this callback handling.
 * @cb:	Callback structure.
 *
 * This function registers a callback to device type. On very first call
 * it will register a misc device, which is used for user kernel interface.
 * Other calls simply increment ref count. Registry will fail, if the user
 * already opened misc device for operation. Also if the misc device
 * creation failed, then it will not try again and all callers will get
 * failure code.
 *
 * Return: Return the return value from the misc creation device or -EINVAL
 * for unsupported device type.
 */
int isst_if_cdev_register(int device_type, struct isst_if_cmd_cb *cb)
{
	if (misc_device_ret)
		return misc_device_ret;

	if (device_type >= ISST_IF_DEV_MAX)
		return -EINVAL;

	mutex_lock(&punit_misc_dev_lock);
	if (misc_device_open) {
		mutex_unlock(&punit_misc_dev_lock);
		return -EAGAIN;
	}
	if (!misc_usage_count) {
		misc_device_ret = misc_register(&isst_if_char_driver);
		if (misc_device_ret)
			goto unlock_exit;
	}
	memcpy(&punit_callbacks[device_type], cb, sizeof(*cb));
	punit_callbacks[device_type].registered = 1;
	misc_usage_count++;
unlock_exit:
	mutex_unlock(&punit_misc_dev_lock);

	return misc_device_ret;
}
EXPORT_SYMBOL_GPL(isst_if_cdev_register);

/**
 * isst_if_cdev_unregister() - Unregister callback for IOCTL
 * @device_type: The device type to unregister.
 *
 * This function unregisters the previously registered callback. If this
 * is the last callback unregistering, then misc device is removed.
 *
 * Return: None.
 */
void isst_if_cdev_unregister(int device_type)
{
	mutex_lock(&punit_misc_dev_lock);
	misc_usage_count--;
	punit_callbacks[device_type].registered = 0;
	if (!misc_usage_count && !misc_device_ret)
		misc_deregister(&isst_if_char_driver);
	mutex_unlock(&punit_misc_dev_lock);
}
EXPORT_SYMBOL_GPL(isst_if_cdev_unregister);

MODULE_LICENSE("GPL v2");