// SPDX-License-Identifier: GPL-2.0-or-later
/* ----------------------------------------------------------------------- *
 *
 *   Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
 *
 * ----------------------------------------------------------------------- */

/*
 * x86 CPUID access device
 *
 * This device is accessed by lseek() to the appropriate CPUID level
 * and then read in chunks of 16 bytes.  A larger size means multiple
 * reads of consecutive levels.
 *
 * The lower 32 bits of the file position is used as the incoming %eax,
 * and the upper 32 bits of the file position as the incoming %ecx,
 * the latter intended for "counting" eax levels like eax=4.
 *
 * This driver uses /dev/cpu/%d/cpuid where %d is the minor number, and on
 * an SMP box will direct the access to CPU %d.
 */

#include <linux/module.h>

#include <linux/types.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/init.h>
#include <linux/poll.h>
#include <linux/smp.h>
#include <linux/major.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/uaccess.h>
#include <linux/gfp.h>
#include <linux/completion.h>

#include <asm/processor.h>
#include <asm/msr.h>

static enum cpuhp_state cpuhp_cpuid_state;

struct cpuid_regs_done {
        struct cpuid_regs regs;
        struct completion done;
};

static void cpuid_smp_cpuid(void *cmd_block)
{
        struct cpuid_regs_done *cmd = cmd_block;

        cpuid_count(cmd->regs.eax, cmd->regs.ecx,
                    &cmd->regs.eax, &cmd->regs.ebx,
                    &cmd->regs.ecx, &cmd->regs.edx);

        complete(&cmd->done);
}

static ssize_t cpuid_read(struct file *file, char __user *buf,
                          size_t count, loff_t *ppos)
{
        char __user *tmp = buf;
        struct cpuid_regs_done cmd;
        int cpu = iminor(file_inode(file));
        u64 pos = *ppos;
        ssize_t bytes = 0;
        int err = 0;

        if (count % 16)
                return -EINVAL; /* Invalid chunk size */

        init_completion(&cmd.done);
        for (; count; count -= 16) {
                call_single_data_t csd;

                INIT_CSD(&csd, cpuid_smp_cpuid, &cmd);

                cmd.regs.eax = pos;
                cmd.regs.ecx = pos >> 32;

                err = smp_call_function_single_async(cpu, &csd);
                if (err)
                        break;
                wait_for_completion(&cmd.done);
                if (copy_to_user(tmp, &cmd.regs, 16)) {
                        err = -EFAULT;
                        break;
                }
                tmp += 16;
                bytes += 16;
                *ppos = ++pos;
                reinit_completion(&cmd.done);
        }

        return bytes ? bytes : err;
}

static int cpuid_open(struct inode *inode, struct file *file)
{
        unsigned int cpu;
        struct cpuinfo_x86 *c;

        cpu = iminor(file_inode(file));
        if (cpu >= nr_cpu_ids || !cpu_online(cpu))
                return -ENXIO;  /* No such CPU */

        c = &cpu_data(cpu);
        if (c->cpuid_level < 0)
                return -EIO;    /* CPUID not supported */

        return 0;
}

/*
 * File operations we support
 */
static const struct file_operations cpuid_fops = {
        .owner = THIS_MODULE,
        .llseek = no_seek_end_llseek,
        .read = cpuid_read,
        .open = cpuid_open,
};

static char *cpuid_devnode(const struct device *dev, umode_t *mode)
{
        return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt));
}

static const struct class cpuid_class = {
        .name           = "cpuid",
        .devnode        = cpuid_devnode,
};

static int cpuid_device_create(unsigned int cpu)
{
        struct device *dev;

        dev = device_create(&cpuid_class, NULL, MKDEV(CPUID_MAJOR, cpu), NULL,
                            "cpu%d", cpu);
        return PTR_ERR_OR_ZERO(dev);
}

static int cpuid_device_destroy(unsigned int cpu)
{
        device_destroy(&cpuid_class, MKDEV(CPUID_MAJOR, cpu));
        return 0;
}

static int __init cpuid_init(void)
{
        int err;

        if (__register_chrdev(CPUID_MAJOR, 0, NR_CPUS,
                              "cpu/cpuid", &cpuid_fops)) {
                printk(KERN_ERR "cpuid: unable to get major %d for cpuid\n",
                       CPUID_MAJOR);
                return -EBUSY;
        }
        err = class_register(&cpuid_class);
        if (err)
                goto out_chrdev;

        err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/cpuid:online",
                                cpuid_device_create, cpuid_device_destroy);
        if (err < 0)
                goto out_class;

        cpuhp_cpuid_state = err;
        return 0;

out_class:
        class_unregister(&cpuid_class);
out_chrdev:
        __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
        return err;
}
module_init(cpuid_init);

static void __exit cpuid_exit(void)
{
        cpuhp_remove_state(cpuhp_cpuid_state);
        class_unregister(&cpuid_class);
        __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
}
module_exit(cpuid_exit);

MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
MODULE_DESCRIPTION("x86 generic CPUID driver");
MODULE_LICENSE("GPL");