// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * rtc-efi: RTC Class Driver for EFI-based systems
 *
 * Copyright (C) 2009 Hewlett-Packard Development Company, L.P.
 *
 * Author: dann frazier <dannf@dannf.org>
 * Based on efirtc.c by Stephane Eranian
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/stringify.h>
#include <linux/time.h>
#include <linux/platform_device.h>
#include <linux/rtc.h>
#include <linux/efi.h>

#define EFI_ISDST (EFI_TIME_ADJUST_DAYLIGHT|EFI_TIME_IN_DAYLIGHT)

/*
 * returns day of the year [0-365]
 */
static inline int
compute_yday(efi_time_t *eft)
{
        /* efi_time_t.month is in the [1-12] so, we need -1 */
        return rtc_year_days(eft->day, eft->month - 1, eft->year);
}

/*
 * returns day of the week [0-6] 0=Sunday
 */
static int
compute_wday(efi_time_t *eft, int yday)
{
        int ndays = eft->year * (365 % 7)
                    + (eft->year - 1) / 4
                    - (eft->year - 1) / 100
                    + (eft->year - 1) / 400
                    + yday;

        /*
         * 1/1/0000 may or may not have been a Sunday (if it ever existed at
         * all) but assuming it was makes this calculation work correctly.
         */
        return ndays % 7;
}

static void
convert_to_efi_time(struct rtc_time *wtime, efi_time_t *eft)
{
        eft->year       = wtime->tm_year + 1900;
        eft->month      = wtime->tm_mon + 1;
        eft->day        = wtime->tm_mday;
        eft->hour       = wtime->tm_hour;
        eft->minute     = wtime->tm_min;
        eft->second     = wtime->tm_sec;
        eft->nanosecond = 0;
        eft->daylight   = wtime->tm_isdst ? EFI_ISDST : 0;
        eft->timezone   = EFI_UNSPECIFIED_TIMEZONE;
}

static bool
convert_from_efi_time(efi_time_t *eft, struct rtc_time *wtime)
{
        memset(wtime, 0, sizeof(*wtime));

        if (eft->second >= 60)
                return false;
        wtime->tm_sec  = eft->second;

        if (eft->minute >= 60)
                return false;
        wtime->tm_min  = eft->minute;

        if (eft->hour >= 24)
                return false;
        wtime->tm_hour = eft->hour;

        if (!eft->day || eft->day > 31)
                return false;
        wtime->tm_mday = eft->day;

        if (!eft->month || eft->month > 12)
                return false;
        wtime->tm_mon  = eft->month - 1;

        if (eft->year < 1900 || eft->year > 9999)
                return false;
        wtime->tm_year = eft->year - 1900;

        /* day in the year [1-365]*/
        wtime->tm_yday = compute_yday(eft);

        /* day of the week [0-6], Sunday=0 */
        wtime->tm_wday = compute_wday(eft, wtime->tm_yday);

        switch (eft->daylight & EFI_ISDST) {
        case EFI_ISDST:
                wtime->tm_isdst = 1;
                break;
        case EFI_TIME_ADJUST_DAYLIGHT:
                wtime->tm_isdst = 0;
                break;
        default:
                wtime->tm_isdst = -1;
        }

        return true;
}

static int efi_read_time(struct device *dev, struct rtc_time *tm)
{
        efi_status_t status;
        efi_time_t eft;
        efi_time_cap_t cap;

        status = efi.get_time(&eft, &cap);

        if (status != EFI_SUCCESS) {
                /* should never happen */
                dev_err_once(dev, "can't read time\n");
                return -EINVAL;
        }

        if (!convert_from_efi_time(&eft, tm))
                return -EIO;

        return 0;
}

static int efi_set_time(struct device *dev, struct rtc_time *tm)
{
        efi_status_t status;
        efi_time_t eft;

        convert_to_efi_time(tm, &eft);

        status = efi.set_time(&eft);

        return status == EFI_SUCCESS ? 0 : -EINVAL;
}

static int efi_procfs(struct device *dev, struct seq_file *seq)
{
        efi_time_t        eft;
        efi_time_cap_t    cap;

        memset(&eft, 0, sizeof(eft));
        memset(&cap, 0, sizeof(cap));

        efi.get_time(&eft, &cap);

        seq_printf(seq,
                   "Time\t\t: %u:%u:%u.%09u\n"
                   "Date\t\t: %u-%u-%u\n"
                   "Daylight\t: %u\n",
                   eft.hour, eft.minute, eft.second, eft.nanosecond,
                   eft.year, eft.month, eft.day,
                   eft.daylight);

        if (eft.timezone == EFI_UNSPECIFIED_TIMEZONE)
                seq_puts(seq, "Timezone\t: unspecified\n");
        else
                /* XXX fixme: convert to string? */
                seq_printf(seq, "Timezone\t: %u\n", eft.timezone);

        /*
         * now prints the capabilities
         */
        seq_printf(seq,
                   "Resolution\t: %u\n"
                   "Accuracy\t: %u\n"
                   "SetstoZero\t: %u\n",
                   cap.resolution, cap.accuracy, cap.sets_to_zero);

        return 0;
}

static const struct rtc_class_ops efi_rtc_ops = {
        .read_time      = efi_read_time,
        .set_time       = efi_set_time,
        .proc           = efi_procfs,
};

static int __init efi_rtc_probe(struct platform_device *dev)
{
        struct rtc_device *rtc;
        efi_time_t eft;
        efi_time_cap_t cap;

        /* First check if the RTC is usable */
        if (efi.get_time(&eft, &cap) != EFI_SUCCESS)
                return -ENODEV;

        rtc = devm_rtc_allocate_device(&dev->dev);
        if (IS_ERR(rtc))
                return PTR_ERR(rtc);

        platform_set_drvdata(dev, rtc);

        rtc->ops = &efi_rtc_ops;
        clear_bit(RTC_FEATURE_ALARM, rtc->features);

        device_init_wakeup(&dev->dev, true);

        return devm_rtc_register_device(rtc);
}

static struct platform_driver efi_rtc_driver = {
        .driver = {
                .name = "rtc-efi",
        },
};

module_platform_driver_probe(efi_rtc_driver, efi_rtc_probe);

MODULE_AUTHOR("dann frazier <dannf@dannf.org>");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("EFI RTC driver");
MODULE_ALIAS("platform:rtc-efi");