// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Hardware monitoring driver for LattePanda Sigma EC.
 *
 * The LattePanda Sigma is an x86 SBC made by DFRobot with an ITE IT8613E
 * Embedded Controller that manages a CPU fan and thermal sensors.
 *
 * The BIOS declares the ACPI Embedded Controller (PNP0C09) with _STA
 * returning 0 and provides only stub ECRD/ECWT methods that return Zero
 * for all registers. Since the kernel's ACPI EC subsystem never initializes,
 * ec_read() is not available and direct port I/O to the standard ACPI EC
 * ports (0x62/0x66) is used instead.
 *
 * Because ACPI never initializes the EC, there is no concurrent firmware
 * access to these ports, and no ACPI Global Lock or namespace mutex is
 * required. The hwmon with_info API serializes all sysfs callbacks,
 * so no additional driver-level locking is needed.
 *
 * The EC register map was discovered by dumping all 256 registers,
 * identifying those that change in real-time, and validating by physically
 * stopping the fan and observing the RPM register drop to zero. The map
 * has been verified on BIOS version 5.27; other versions may differ.
 *
 * Copyright (c) 2026 Mariano Abad <weimaraner@gmail.com>
 */

#include <linux/delay.h>
#include <linux/dmi.h>
#include <linux/hwmon.h>
#include <linux/io.h>
#include <linux/ioport.h>
#include <linux/module.h>
#include <linux/platform_device.h>

#define DRIVER_NAME     "lattepanda_sigma_ec"

/* EC I/O ports (standard ACPI EC interface) */
#define EC_DATA_PORT    0x62
#define EC_CMD_PORT     0x66    /* also status port */

/* EC commands */
#define EC_CMD_READ     0x80

/* EC status register bits */
#define EC_STATUS_OBF   0x01    /* Output Buffer Full */
#define EC_STATUS_IBF   0x02    /* Input Buffer Full */

/* EC register offsets for LattePanda Sigma (BIOS 5.27) */
#define EC_REG_FAN_RPM_HI       0x2E
#define EC_REG_FAN_RPM_LO       0x2F
#define EC_REG_TEMP_BOARD       0x60
#define EC_REG_TEMP_CPU         0x70
#define EC_REG_FAN_DUTY         0x93

/*
 * EC polling uses udelay() because the EC typically responds within a
 * few microseconds. The kernel's own ACPI EC driver (drivers/acpi/ec.c)
 * likewise uses udelay() for busy-polling with a per-poll delay of 550us.
 *
 * usleep_range() was tested but caused EC protocol failures: the EC
 * clears its status flags within microseconds, and sleeping for 50-100us
 * between polls allowed the flags to transition past the expected state.
 *
 * The worst-case total busy-wait of 25ms covers EC recovery after errors.
 * In practice the EC responds within 10us so the loop exits immediately.
 */
#define EC_TIMEOUT_US           25000
#define EC_POLL_US              1

static bool force;
module_param(force, bool, 0444);
MODULE_PARM_DESC(force,
                 "Force loading on untested BIOS versions (default: false)");

static struct platform_device *lps_ec_pdev;

static int ec_wait_ibf_clear(void)
{
        int i;

        for (i = 0; i < EC_TIMEOUT_US; i++) {
                if (!(inb(EC_CMD_PORT) & EC_STATUS_IBF))
                        return 0;
                udelay(EC_POLL_US);
        }
        return -ETIMEDOUT;
}

static int ec_wait_obf_set(void)
{
        int i;

        for (i = 0; i < EC_TIMEOUT_US; i++) {
                if (inb(EC_CMD_PORT) & EC_STATUS_OBF)
                        return 0;
                udelay(EC_POLL_US);
        }
        return -ETIMEDOUT;
}

static int ec_read_reg(u8 reg, u8 *val)
{
        int ret;

        ret = ec_wait_ibf_clear();
        if (ret)
                return ret;

        outb(EC_CMD_READ, EC_CMD_PORT);

        ret = ec_wait_ibf_clear();
        if (ret)
                return ret;

        outb(reg, EC_DATA_PORT);

        ret = ec_wait_obf_set();
        if (ret)
                return ret;

        *val = inb(EC_DATA_PORT);
        return 0;
}

/*
 * Read a 16-bit big-endian value from two consecutive EC registers.
 *
 * The EC may update the register pair between reading the high and low
 * bytes, which could produce a corrupted value if the high byte rolls
 * over (e.g., 0x0100 -> 0x00FF read as 0x01FF). Guard against this by
 * re-reading the high byte after reading the low byte. If the high byte
 * changed, re-read the low byte to get a consistent pair.
 * See also lm90_read16() which uses the same approach.
 */
static int ec_read_reg16(u8 reg_hi, u8 reg_lo, u16 *val)
{
        int ret;
        u8 oldh, newh, lo;

        ret = ec_read_reg(reg_hi, &oldh);
        if (ret)
                return ret;

        ret = ec_read_reg(reg_lo, &lo);
        if (ret)
                return ret;

        ret = ec_read_reg(reg_hi, &newh);
        if (ret)
                return ret;

        if (oldh != newh) {
                ret = ec_read_reg(reg_lo, &lo);
                if (ret)
                        return ret;
        }

        *val = ((u16)newh << 8) | lo;
        return 0;
}

static int
lps_ec_read_string(struct device *dev,
                   enum hwmon_sensor_types type,
                   u32 attr, int channel,
                   const char **str)
{
        switch (type) {
        case hwmon_fan:
                *str = "CPU Fan";
                return 0;
        case hwmon_temp:
                *str = channel == 0 ? "Board Temp" : "CPU Temp";
                return 0;
        default:
                return -EOPNOTSUPP;
        }
}

static umode_t
lps_ec_is_visible(const void *drvdata,
                  enum hwmon_sensor_types type,
                  u32 attr, int channel)
{
        switch (type) {
        case hwmon_fan:
                if (attr == hwmon_fan_input || attr == hwmon_fan_label)
                        return 0444;
                break;
        case hwmon_temp:
                if (attr == hwmon_temp_input || attr == hwmon_temp_label)
                        return 0444;
                break;
        default:
                break;
        }
        return 0;
}

static int
lps_ec_read(struct device *dev,
            enum hwmon_sensor_types type,
            u32 attr, int channel, long *val)
{
        u16 rpm;
        u8 v;
        int ret;

        switch (type) {
        case hwmon_fan:
                if (attr != hwmon_fan_input)
                        return -EOPNOTSUPP;
                ret = ec_read_reg16(EC_REG_FAN_RPM_HI,
                                    EC_REG_FAN_RPM_LO, &rpm);
                if (ret)
                        return ret;
                *val = rpm;
                return 0;

        case hwmon_temp:
                if (attr != hwmon_temp_input)
                        return -EOPNOTSUPP;
                ret = ec_read_reg(channel == 0 ? EC_REG_TEMP_BOARD
                                               : EC_REG_TEMP_CPU,
                                  &v);
                if (ret)
                        return ret;
                /* EC reports unsigned 8-bit temperature in degrees Celsius */
                *val = (unsigned long)v * 1000;
                return 0;

        default:
                return -EOPNOTSUPP;
        }
}

static const struct hwmon_channel_info * const lps_ec_info[] = {
        HWMON_CHANNEL_INFO(fan, HWMON_F_INPUT | HWMON_F_LABEL),
        HWMON_CHANNEL_INFO(temp,
                           HWMON_T_INPUT | HWMON_T_LABEL,
                           HWMON_T_INPUT | HWMON_T_LABEL),
        NULL
};

static const struct hwmon_ops lps_ec_ops = {
        .is_visible = lps_ec_is_visible,
        .read = lps_ec_read,
        .read_string = lps_ec_read_string,
};

static const struct hwmon_chip_info lps_ec_chip_info = {
        .ops = &lps_ec_ops,
        .info = lps_ec_info,
};

static int lps_ec_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct device *hwmon;
        u8 test;
        int ret;

        if (!devm_request_region(dev, EC_DATA_PORT, 1, DRIVER_NAME))
                return dev_err_probe(dev, -EBUSY,
                                     "Failed to request EC data port 0x%x\n",
                                     EC_DATA_PORT);

        if (!devm_request_region(dev, EC_CMD_PORT, 1, DRIVER_NAME))
                return dev_err_probe(dev, -EBUSY,
                                     "Failed to request EC cmd port 0x%x\n",
                                     EC_CMD_PORT);

        /* Sanity check: verify EC is responsive */
        ret = ec_read_reg(EC_REG_FAN_DUTY, &test);
        if (ret)
                return dev_err_probe(dev, ret,
                                     "EC not responding on ports 0x%x/0x%x\n",
                                     EC_DATA_PORT, EC_CMD_PORT);

        hwmon = devm_hwmon_device_register_with_info(dev, DRIVER_NAME, NULL,
                                                     &lps_ec_chip_info, NULL);
        if (IS_ERR(hwmon))
                return dev_err_probe(dev, PTR_ERR(hwmon),
                                     "Failed to register hwmon device\n");

        dev_info(dev, "EC hwmon registered (fan duty: %u%%)\n", test);
        return 0;
}

/* DMI table with strict BIOS version match (override with force=1) */
static const struct dmi_system_id lps_ec_dmi_table[] = {
        {
                .ident = "LattePanda Sigma",
                .matches = {
                        DMI_MATCH(DMI_SYS_VENDOR, "LattePanda"),
                        DMI_MATCH(DMI_PRODUCT_NAME, "LattePanda Sigma"),
                        DMI_MATCH(DMI_BIOS_VERSION, "5.27"),
                },
        },
        { }     /* terminator */
};
MODULE_DEVICE_TABLE(dmi, lps_ec_dmi_table);

/* Loose table (vendor + product only) for use with force=1 */
static const struct dmi_system_id lps_ec_dmi_table_force[] = {
        {
                .ident = "LattePanda Sigma",
                .matches = {
                        DMI_MATCH(DMI_SYS_VENDOR, "LattePanda"),
                        DMI_MATCH(DMI_PRODUCT_NAME, "LattePanda Sigma"),
                },
        },
        { }     /* terminator */
};

static struct platform_driver lps_ec_driver = {
        .probe  = lps_ec_probe,
        .driver = {
                .name = DRIVER_NAME,
        },
};

static int __init lps_ec_init(void)
{
        int ret;

        if (!dmi_check_system(lps_ec_dmi_table)) {
                if (!force || !dmi_check_system(lps_ec_dmi_table_force))
                        return -ENODEV;
                pr_warn("%s: BIOS version not verified, loading due to force=1\n",
                        DRIVER_NAME);
        }

        ret = platform_driver_register(&lps_ec_driver);
        if (ret)
                return ret;

        lps_ec_pdev = platform_device_register_simple(DRIVER_NAME, -1,
                                                      NULL, 0);
        if (IS_ERR(lps_ec_pdev)) {
                platform_driver_unregister(&lps_ec_driver);
                return PTR_ERR(lps_ec_pdev);
        }

        return 0;
}

static void __exit lps_ec_exit(void)
{
        platform_device_unregister(lps_ec_pdev);
        platform_driver_unregister(&lps_ec_driver);
}

module_init(lps_ec_init);
module_exit(lps_ec_exit);

MODULE_AUTHOR("Mariano Abad <weimaraner@gmail.com>");
MODULE_DESCRIPTION("Hardware monitoring driver for LattePanda Sigma EC");
MODULE_LICENSE("GPL");