// SPDX-License-Identifier: GPL-2.0-only
/*
 * bios-less APM driver for ARM Linux
 *  Jamey Hicks <jamey@crl.dec.com>
 *  adapted from the APM BIOS driver for Linux by Stephen Rothwell (sfr@linuxcare.com)
 *
 * APM 1.2 Reference:
 *   Intel Corporation, Microsoft Corporation. Advanced Power Management
 *   (APM) BIOS Interface Specification, Revision 1.2, February 1996.
 *
 * This document is available from Microsoft at:
 *    http://www.microsoft.com/whdc/archive/amp_12.mspx
 */
#include <linux/module.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/miscdevice.h>
#include <linux/apm_bios.h>
#include <linux/capability.h>
#include <linux/sched.h>
#include <linux/suspend.h>
#include <linux/apm-emulation.h>
#include <linux/freezer.h>
#include <linux/device.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/completion.h>
#include <linux/kthread.h>
#include <linux/delay.h>

/*
 * One option can be changed at boot time as follows:
 *      apm=on/off                      enable/disable APM
 */

/*
 * Maximum number of events stored
 */
#define APM_MAX_EVENTS          16

struct apm_queue {
        unsigned int            event_head;
        unsigned int            event_tail;
        apm_event_t             events[APM_MAX_EVENTS];
};

/*
 * thread states (for threads using a writable /dev/apm_bios fd):
 *
 * SUSPEND_NONE:        nothing happening
 * SUSPEND_PENDING:     suspend event queued for thread and pending to be read
 * SUSPEND_READ:        suspend event read, pending acknowledgement
 * SUSPEND_ACKED:       acknowledgement received from thread (via ioctl),
 *                      waiting for resume
 * SUSPEND_ACKTO:       acknowledgement timeout
 * SUSPEND_DONE:        thread had acked suspend and is now notified of
 *                      resume
 *
 * SUSPEND_WAIT:        this thread invoked suspend and is waiting for resume
 *
 * A thread migrates in one of three paths:
 *      NONE -1-> PENDING -2-> READ -3-> ACKED -4-> DONE -5-> NONE
 *                                  -6-> ACKTO -7-> NONE
 *      NONE -8-> WAIT -9-> NONE
 *
 * While in PENDING or READ, the thread is accounted for in the
 * suspend_acks_pending counter.
 *
 * The transitions are invoked as follows:
 *      1: suspend event is signalled from the core PM code
 *      2: the suspend event is read from the fd by the userspace thread
 *      3: userspace thread issues the APM_IOC_SUSPEND ioctl (as ack)
 *      4: core PM code signals that we have resumed
 *      5: APM_IOC_SUSPEND ioctl returns
 *
 *      6: the notifier invoked from the core PM code timed out waiting
 *         for all relevant threds to enter ACKED state and puts those
 *         that haven't into ACKTO
 *      7: those threads issue APM_IOC_SUSPEND ioctl too late,
 *         get an error
 *
 *      8: userspace thread issues the APM_IOC_SUSPEND ioctl (to suspend),
 *         ioctl code invokes pm_suspend()
 *      9: pm_suspend() returns indicating resume
 */
enum apm_suspend_state {
        SUSPEND_NONE,
        SUSPEND_PENDING,
        SUSPEND_READ,
        SUSPEND_ACKED,
        SUSPEND_ACKTO,
        SUSPEND_WAIT,
        SUSPEND_DONE,
};

/*
 * The per-file APM data
 */
struct apm_user {
        struct list_head        list;

        unsigned int            suser: 1;
        unsigned int            writer: 1;
        unsigned int            reader: 1;

        int                     suspend_result;
        enum apm_suspend_state  suspend_state;

        struct apm_queue        queue;
};

/*
 * Local variables
 */
static atomic_t suspend_acks_pending = ATOMIC_INIT(0);
static atomic_t userspace_notification_inhibit = ATOMIC_INIT(0);
static int apm_disabled;
static struct task_struct *kapmd_tsk;

static DECLARE_WAIT_QUEUE_HEAD(apm_waitqueue);
static DECLARE_WAIT_QUEUE_HEAD(apm_suspend_waitqueue);

/*
 * This is a list of everyone who has opened /dev/apm_bios
 */
static DECLARE_RWSEM(user_list_lock);
static LIST_HEAD(apm_user_list);

/*
 * kapmd info.  kapmd provides us a process context to handle
 * "APM" events within - specifically necessary if we're going
 * to be suspending the system.
 */
static DECLARE_WAIT_QUEUE_HEAD(kapmd_wait);
static DEFINE_SPINLOCK(kapmd_queue_lock);
static struct apm_queue kapmd_queue;

static DEFINE_MUTEX(state_lock);


/*
 * This allows machines to provide their own "apm get power status" function.
 */
void (*apm_get_power_status)(struct apm_power_info *);
EXPORT_SYMBOL(apm_get_power_status);


/*
 * APM event queue management.
 */
static inline int queue_empty(struct apm_queue *q)
{
        return q->event_head == q->event_tail;
}

static inline apm_event_t queue_get_event(struct apm_queue *q)
{
        q->event_tail = (q->event_tail + 1) % APM_MAX_EVENTS;
        return q->events[q->event_tail];
}

static void queue_add_event(struct apm_queue *q, apm_event_t event)
{
        q->event_head = (q->event_head + 1) % APM_MAX_EVENTS;
        if (q->event_head == q->event_tail) {
                static int notified;

                if (notified++ == 0)
                    printk(KERN_ERR "apm: an event queue overflowed\n");
                q->event_tail = (q->event_tail + 1) % APM_MAX_EVENTS;
        }
        q->events[q->event_head] = event;
}

static void queue_event(apm_event_t event)
{
        struct apm_user *as;

        down_read(&user_list_lock);
        list_for_each_entry(as, &apm_user_list, list) {
                if (as->reader)
                        queue_add_event(&as->queue, event);
        }
        up_read(&user_list_lock);
        wake_up_interruptible(&apm_waitqueue);
}

static ssize_t apm_read(struct file *fp, char __user *buf, size_t count, loff_t *ppos)
{
        struct apm_user *as = fp->private_data;
        apm_event_t event;
        int i = count, ret = 0;

        if (count < sizeof(apm_event_t))
                return -EINVAL;

        if (queue_empty(&as->queue) && fp->f_flags & O_NONBLOCK)
                return -EAGAIN;

        wait_event_interruptible(apm_waitqueue, !queue_empty(&as->queue));

        while ((i >= sizeof(event)) && !queue_empty(&as->queue)) {
                event = queue_get_event(&as->queue);

                ret = -EFAULT;
                if (copy_to_user(buf, &event, sizeof(event)))
                        break;

                mutex_lock(&state_lock);
                if (as->suspend_state == SUSPEND_PENDING &&
                    (event == APM_SYS_SUSPEND || event == APM_USER_SUSPEND))
                        as->suspend_state = SUSPEND_READ;
                mutex_unlock(&state_lock);

                buf += sizeof(event);
                i -= sizeof(event);
        }

        if (i < count)
                ret = count - i;

        return ret;
}

static __poll_t apm_poll(struct file *fp, poll_table * wait)
{
        struct apm_user *as = fp->private_data;

        poll_wait(fp, &apm_waitqueue, wait);
        return queue_empty(&as->queue) ? 0 : EPOLLIN | EPOLLRDNORM;
}

/*
 * apm_ioctl - handle APM ioctl
 *
 * APM_IOC_SUSPEND
 *   This IOCTL is overloaded, and performs two functions.  It is used to:
 *     - initiate a suspend
 *     - acknowledge a suspend read from /dev/apm_bios.
 *   Only when everyone who has opened /dev/apm_bios with write permission
 *   has acknowledge does the actual suspend happen.
 */
static long
apm_ioctl(struct file *filp, u_int cmd, u_long arg)
{
        struct apm_user *as = filp->private_data;
        int err = -EINVAL;

        if (!as->suser || !as->writer)
                return -EPERM;

        switch (cmd) {
        case APM_IOC_SUSPEND:
                mutex_lock(&state_lock);

                as->suspend_result = -EINTR;

                switch (as->suspend_state) {
                case SUSPEND_READ:
                        /*
                         * If we read a suspend command from /dev/apm_bios,
                         * then the corresponding APM_IOC_SUSPEND ioctl is
                         * interpreted as an acknowledge.
                         */
                        as->suspend_state = SUSPEND_ACKED;
                        atomic_dec(&suspend_acks_pending);
                        mutex_unlock(&state_lock);

                        /*
                         * suspend_acks_pending changed, the notifier needs to
                         * be woken up for this
                         */
                        wake_up(&apm_suspend_waitqueue);

                        /*
                         * Wait for the suspend/resume to complete.  If there
                         * are pending acknowledges, we wait here for them.
                         * wait_event_freezable() is interruptible and pending
                         * signal can cause busy looping.  We aren't doing
                         * anything critical, chill a bit on each iteration.
                         */
                        while (wait_event_freezable(apm_suspend_waitqueue,
                                        as->suspend_state != SUSPEND_ACKED))
                                msleep(10);
                        break;
                case SUSPEND_ACKTO:
                        as->suspend_result = -ETIMEDOUT;
                        mutex_unlock(&state_lock);
                        break;
                default:
                        as->suspend_state = SUSPEND_WAIT;
                        mutex_unlock(&state_lock);

                        /*
                         * Otherwise it is a request to suspend the system.
                         * Just invoke pm_suspend(), we'll handle it from
                         * there via the notifier.
                         */
                        as->suspend_result = pm_suspend(PM_SUSPEND_MEM);
                }

                mutex_lock(&state_lock);
                err = as->suspend_result;
                as->suspend_state = SUSPEND_NONE;
                mutex_unlock(&state_lock);
                break;
        }

        return err;
}

static int apm_release(struct inode * inode, struct file * filp)
{
        struct apm_user *as = filp->private_data;

        filp->private_data = NULL;

        down_write(&user_list_lock);
        list_del(&as->list);
        up_write(&user_list_lock);

        /*
         * We are now unhooked from the chain.  As far as new
         * events are concerned, we no longer exist.
         */
        mutex_lock(&state_lock);
        if (as->suspend_state == SUSPEND_PENDING ||
            as->suspend_state == SUSPEND_READ)
                atomic_dec(&suspend_acks_pending);
        mutex_unlock(&state_lock);

        wake_up(&apm_suspend_waitqueue);

        kfree(as);
        return 0;
}

static int apm_open(struct inode * inode, struct file * filp)
{
        struct apm_user *as;

        as = kzalloc_obj(*as);
        if (as) {
                /*
                 * XXX - this is a tiny bit broken, when we consider BSD
                 * process accounting. If the device is opened by root, we
                 * instantly flag that we used superuser privs. Who knows,
                 * we might close the device immediately without doing a
                 * privileged operation -- cevans
                 */
                as->suser = capable(CAP_SYS_ADMIN);
                as->writer = (filp->f_mode & FMODE_WRITE) == FMODE_WRITE;
                as->reader = (filp->f_mode & FMODE_READ) == FMODE_READ;

                down_write(&user_list_lock);
                list_add(&as->list, &apm_user_list);
                up_write(&user_list_lock);

                filp->private_data = as;
        }

        return as ? 0 : -ENOMEM;
}

static const struct file_operations apm_bios_fops = {
        .owner          = THIS_MODULE,
        .read           = apm_read,
        .poll           = apm_poll,
        .unlocked_ioctl = apm_ioctl,
        .open           = apm_open,
        .release        = apm_release,
        .llseek         = noop_llseek,
};

static struct miscdevice apm_device = {
        .minor          = APM_MINOR_DEV,
        .name           = "apm_bios",
        .fops           = &apm_bios_fops
};


#ifdef CONFIG_PROC_FS
/*
 * Arguments, with symbols from linux/apm_bios.h.
 *
 *   0) Linux driver version (this will change if format changes)
 *   1) APM BIOS Version.  Usually 1.0, 1.1 or 1.2.
 *   2) APM flags from APM Installation Check (0x00):
 *      bit 0: APM_16_BIT_SUPPORT
 *      bit 1: APM_32_BIT_SUPPORT
 *      bit 2: APM_IDLE_SLOWS_CLOCK
 *      bit 3: APM_BIOS_DISABLED
 *      bit 4: APM_BIOS_DISENGAGED
 *   3) AC line status
 *      0x00: Off-line
 *      0x01: On-line
 *      0x02: On backup power (BIOS >= 1.1 only)
 *      0xff: Unknown
 *   4) Battery status
 *      0x00: High
 *      0x01: Low
 *      0x02: Critical
 *      0x03: Charging
 *      0x04: Selected battery not present (BIOS >= 1.2 only)
 *      0xff: Unknown
 *   5) Battery flag
 *      bit 0: High
 *      bit 1: Low
 *      bit 2: Critical
 *      bit 3: Charging
 *      bit 7: No system battery
 *      0xff: Unknown
 *   6) Remaining battery life (percentage of charge):
 *      0-100: valid
 *      -1: Unknown
 *   7) Remaining battery life (time units):
 *      Number of remaining minutes or seconds
 *      -1: Unknown
 *   8) min = minutes; sec = seconds
 */
static int proc_apm_show(struct seq_file *m, void *v)
{
        static const char driver_version[] = "1.13";    /* no spaces */

        struct apm_power_info info;
        char *units;

        info.ac_line_status = 0xff;
        info.battery_status = 0xff;
        info.battery_flag   = 0xff;
        info.battery_life   = -1;
        info.time           = -1;
        info.units          = -1;

        if (apm_get_power_status)
                apm_get_power_status(&info);

        switch (info.units) {
        default:        units = "?";    break;
        case 0:         units = "min";  break;
        case 1:         units = "sec";  break;
        }

        seq_printf(m, "%s 1.2 0x%02x 0x%02x 0x%02x 0x%02x %d%% %d %s\n",
                     driver_version, APM_32_BIT_SUPPORT,
                     info.ac_line_status, info.battery_status,
                     info.battery_flag, info.battery_life,
                     info.time, units);

        return 0;
}
#endif

static int kapmd(void *arg)
{
        do {
                apm_event_t event;

                wait_event_interruptible(kapmd_wait,
                                !queue_empty(&kapmd_queue) || kthread_should_stop());

                if (kthread_should_stop())
                        break;

                spin_lock_irq(&kapmd_queue_lock);
                event = 0;
                if (!queue_empty(&kapmd_queue))
                        event = queue_get_event(&kapmd_queue);
                spin_unlock_irq(&kapmd_queue_lock);

                switch (event) {
                case 0:
                        break;

                case APM_LOW_BATTERY:
                case APM_POWER_STATUS_CHANGE:
                        queue_event(event);
                        break;

                case APM_USER_SUSPEND:
                case APM_SYS_SUSPEND:
                        pm_suspend(PM_SUSPEND_MEM);
                        break;

                case APM_CRITICAL_SUSPEND:
                        atomic_inc(&userspace_notification_inhibit);
                        pm_suspend(PM_SUSPEND_MEM);
                        atomic_dec(&userspace_notification_inhibit);
                        break;
                }
        } while (1);

        return 0;
}

static int apm_suspend_notifier(struct notifier_block *nb,
                                unsigned long event,
                                void *dummy)
{
        struct apm_user *as;
        int err;
        unsigned long apm_event;

        /* short-cut emergency suspends */
        if (atomic_read(&userspace_notification_inhibit))
                return NOTIFY_DONE;

        switch (event) {
        case PM_SUSPEND_PREPARE:
        case PM_HIBERNATION_PREPARE:
                apm_event = (event == PM_SUSPEND_PREPARE) ?
                        APM_USER_SUSPEND : APM_USER_HIBERNATION;
                /*
                 * Queue an event to all "writer" users that we want
                 * to suspend and need their ack.
                 */
                mutex_lock(&state_lock);
                down_read(&user_list_lock);

                list_for_each_entry(as, &apm_user_list, list) {
                        if (as->suspend_state != SUSPEND_WAIT && as->reader &&
                            as->writer && as->suser) {
                                as->suspend_state = SUSPEND_PENDING;
                                atomic_inc(&suspend_acks_pending);
                                queue_add_event(&as->queue, apm_event);
                        }
                }

                up_read(&user_list_lock);
                mutex_unlock(&state_lock);
                wake_up_interruptible(&apm_waitqueue);

                /*
                 * Wait for the suspend_acks_pending variable to drop to
                 * zero, meaning everybody acked the suspend event (or the
                 * process was killed.)
                 *
                 * If the app won't answer within a short while we assume it
                 * locked up and ignore it.
                 */
                err = wait_event_interruptible_timeout(
                        apm_suspend_waitqueue,
                        atomic_read(&suspend_acks_pending) == 0,
                        5*HZ);

                /* timed out */
                if (err == 0) {
                        /*
                         * Move anybody who timed out to "ack timeout" state.
                         *
                         * We could time out and the userspace does the ACK
                         * right after we time out but before we enter the
                         * locked section here, but that's fine.
                         */
                        mutex_lock(&state_lock);
                        down_read(&user_list_lock);
                        list_for_each_entry(as, &apm_user_list, list) {
                                if (as->suspend_state == SUSPEND_PENDING ||
                                    as->suspend_state == SUSPEND_READ) {
                                        as->suspend_state = SUSPEND_ACKTO;
                                        atomic_dec(&suspend_acks_pending);
                                }
                        }
                        up_read(&user_list_lock);
                        mutex_unlock(&state_lock);
                }

                /* let suspend proceed */
                if (err >= 0)
                        return NOTIFY_OK;

                /* interrupted by signal */
                return notifier_from_errno(err);

        case PM_POST_SUSPEND:
        case PM_POST_HIBERNATION:
                apm_event = (event == PM_POST_SUSPEND) ?
                        APM_NORMAL_RESUME : APM_HIBERNATION_RESUME;
                /*
                 * Anyone on the APM queues will think we're still suspended.
                 * Send a message so everyone knows we're now awake again.
                 */
                queue_event(apm_event);

                /*
                 * Finally, wake up anyone who is sleeping on the suspend.
                 */
                mutex_lock(&state_lock);
                down_read(&user_list_lock);
                list_for_each_entry(as, &apm_user_list, list) {
                        if (as->suspend_state == SUSPEND_ACKED) {
                                /*
                                 * TODO: maybe grab error code, needs core
                                 * changes to push the error to the notifier
                                 * chain (could use the second parameter if
                                 * implemented)
                                 */
                                as->suspend_result = 0;
                                as->suspend_state = SUSPEND_DONE;
                        }
                }
                up_read(&user_list_lock);
                mutex_unlock(&state_lock);

                wake_up(&apm_suspend_waitqueue);
                return NOTIFY_OK;

        default:
                return NOTIFY_DONE;
        }
}

static struct notifier_block apm_notif_block = {
        .notifier_call = apm_suspend_notifier,
};

static int __init apm_init(void)
{
        int ret;

        if (apm_disabled) {
                printk(KERN_NOTICE "apm: disabled on user request.\n");
                return -ENODEV;
        }

        kapmd_tsk = kthread_create(kapmd, NULL, "kapmd");
        if (IS_ERR(kapmd_tsk)) {
                ret = PTR_ERR(kapmd_tsk);
                kapmd_tsk = NULL;
                goto out;
        }
        wake_up_process(kapmd_tsk);

#ifdef CONFIG_PROC_FS
        proc_create_single("apm", 0, NULL, proc_apm_show);
#endif

        ret = misc_register(&apm_device);
        if (ret)
                goto out_stop;

        ret = register_pm_notifier(&apm_notif_block);
        if (ret)
                goto out_unregister;

        return 0;

 out_unregister:
        misc_deregister(&apm_device);
 out_stop:
        remove_proc_entry("apm", NULL);
        kthread_stop(kapmd_tsk);
 out:
        return ret;
}

static void __exit apm_exit(void)
{
        unregister_pm_notifier(&apm_notif_block);
        misc_deregister(&apm_device);
        remove_proc_entry("apm", NULL);

        kthread_stop(kapmd_tsk);
}

module_init(apm_init);
module_exit(apm_exit);

MODULE_AUTHOR("Stephen Rothwell");
MODULE_DESCRIPTION("Advanced Power Management");
MODULE_LICENSE("GPL");

#ifndef MODULE
static int __init apm_setup(char *str)
{
        while ((str != NULL) && (*str != '\0')) {
                if (strncmp(str, "off", 3) == 0)
                        apm_disabled = 1;
                if (strncmp(str, "on", 2) == 0)
                        apm_disabled = 0;
                str = strchr(str, ',');
                if (str != NULL)
                        str += strspn(str, ", \t");
        }
        return 1;
}

__setup("apm=", apm_setup);
#endif

/**
 * apm_queue_event - queue an APM event for kapmd
 * @event: APM event
 *
 * Queue an APM event for kapmd to process and ultimately take the
 * appropriate action.  Only a subset of events are handled:
 *   %APM_LOW_BATTERY
 *   %APM_POWER_STATUS_CHANGE
 *   %APM_USER_SUSPEND
 *   %APM_SYS_SUSPEND
 *   %APM_CRITICAL_SUSPEND
 */
void apm_queue_event(apm_event_t event)
{
        unsigned long flags;

        spin_lock_irqsave(&kapmd_queue_lock, flags);
        queue_add_event(&kapmd_queue, event);
        spin_unlock_irqrestore(&kapmd_queue_lock, flags);

        wake_up_interruptible(&kapmd_wait);
}
EXPORT_SYMBOL(apm_queue_event);