// SPDX-License-Identifier: GPL-2.0
/*
 * RTC interface for Wilco Embedded Controller with R/W abilities
 *
 * Copyright 2018 Google LLC
 *
 * The corresponding platform device is typically registered in
 * drivers/platform/chrome/wilco_ec/core.c
 */

#include <linux/bcd.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/platform_data/wilco-ec.h>
#include <linux/rtc.h>
#include <linux/timekeeping.h>

#define EC_COMMAND_CMOS                 0x7c
#define EC_CMOS_TOD_WRITE               0x02
#define EC_CMOS_TOD_READ                0x08

/* Message sent to the EC to request the current time. */
struct ec_rtc_read_request {
        u8 command;
        u8 reserved;
        u8 param;
} __packed;
static struct ec_rtc_read_request read_rq = {
        .command = EC_COMMAND_CMOS,
        .param = EC_CMOS_TOD_READ,
};

/**
 * struct ec_rtc_read_response - Format of RTC returned by EC.
 * @reserved: Unused byte
 * @second: Second value (0..59)
 * @minute: Minute value (0..59)
 * @hour: Hour value (0..23)
 * @day: Day value (1..31)
 * @month: Month value (1..12)
 * @year: Year value (full year % 100)
 * @century: Century value (full year / 100)
 *
 * All values are presented in binary (not BCD).
 */
struct ec_rtc_read_response {
        u8 reserved;
        u8 second;
        u8 minute;
        u8 hour;
        u8 day;
        u8 month;
        u8 year;
        u8 century;
} __packed;

/**
 * struct ec_rtc_write_request - Format of RTC sent to the EC.
 * @command: Always EC_COMMAND_CMOS
 * @reserved: Unused byte
 * @param: Always EC_CMOS_TOD_WRITE
 * @century: Century value (full year / 100)
 * @year: Year value (full year % 100)
 * @month: Month value (1..12)
 * @day: Day value (1..31)
 * @hour: Hour value (0..23)
 * @minute: Minute value (0..59)
 * @second: Second value (0..59)
 * @weekday: Day of the week (0=Saturday)
 *
 * All values are presented in BCD.
 */
struct ec_rtc_write_request {
        u8 command;
        u8 reserved;
        u8 param;
        u8 century;
        u8 year;
        u8 month;
        u8 day;
        u8 hour;
        u8 minute;
        u8 second;
        u8 weekday;
} __packed;

static int wilco_ec_rtc_read(struct device *dev, struct rtc_time *tm)
{
        struct wilco_ec_device *ec = dev_get_drvdata(dev->parent);
        struct ec_rtc_read_response rtc;
        struct wilco_ec_message msg;
        int ret;

        memset(&msg, 0, sizeof(msg));
        msg.type = WILCO_EC_MSG_LEGACY;
        msg.request_data = &read_rq;
        msg.request_size = sizeof(read_rq);
        msg.response_data = &rtc;
        msg.response_size = sizeof(rtc);

        ret = wilco_ec_mailbox(ec, &msg);
        if (ret < 0)
                return ret;

        tm->tm_sec      = rtc.second;
        tm->tm_min      = rtc.minute;
        tm->tm_hour     = rtc.hour;
        tm->tm_mday     = rtc.day;
        tm->tm_mon      = rtc.month - 1;
        tm->tm_year     = rtc.year + (rtc.century * 100) - 1900;
        /* Ignore other tm fields, man rtc says userspace shouldn't use them. */

        if (rtc_valid_tm(tm)) {
                dev_err(dev, "Time from RTC is invalid: %ptRr\n", tm);
                return -EIO;
        }

        return 0;
}

static int wilco_ec_rtc_write(struct device *dev, struct rtc_time *tm)
{
        struct wilco_ec_device *ec = dev_get_drvdata(dev->parent);
        struct ec_rtc_write_request rtc;
        struct wilco_ec_message msg;
        int year = tm->tm_year + 1900;
        /*
         * Convert from 0=Sunday to 0=Saturday for the EC
         * We DO need to set weekday because the EC controls battery charging
         * schedules that depend on the day of the week.
         */
        int wday = tm->tm_wday == 6 ? 0 : tm->tm_wday + 1;
        int ret;

        rtc.command     = EC_COMMAND_CMOS;
        rtc.param       = EC_CMOS_TOD_WRITE;
        rtc.century     = bin2bcd(year / 100);
        rtc.year        = bin2bcd(year % 100);
        rtc.month       = bin2bcd(tm->tm_mon + 1);
        rtc.day         = bin2bcd(tm->tm_mday);
        rtc.hour        = bin2bcd(tm->tm_hour);
        rtc.minute      = bin2bcd(tm->tm_min);
        rtc.second      = bin2bcd(tm->tm_sec);
        rtc.weekday     = bin2bcd(wday);

        memset(&msg, 0, sizeof(msg));
        msg.type = WILCO_EC_MSG_LEGACY;
        msg.request_data = &rtc;
        msg.request_size = sizeof(rtc);

        ret = wilco_ec_mailbox(ec, &msg);
        if (ret < 0)
                return ret;

        return 0;
}

static const struct rtc_class_ops wilco_ec_rtc_ops = {
        .read_time = wilco_ec_rtc_read,
        .set_time = wilco_ec_rtc_write,
};

static int wilco_ec_rtc_probe(struct platform_device *pdev)
{
        struct rtc_device *rtc;

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

        rtc->ops = &wilco_ec_rtc_ops;
        /* EC only supports this century */
        rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
        rtc->range_max = RTC_TIMESTAMP_END_2099;
        rtc->owner = THIS_MODULE;

        return devm_rtc_register_device(rtc);
}

static struct platform_driver wilco_ec_rtc_driver = {
        .driver = {
                .name = "rtc-wilco-ec",
        },
        .probe = wilco_ec_rtc_probe,
};

module_platform_driver(wilco_ec_rtc_driver);

MODULE_ALIAS("platform:rtc-wilco-ec");
MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Wilco EC RTC driver");