// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * The Netronix embedded controller is a microcontroller found in some
 * e-book readers designed by the original design manufacturer Netronix, Inc.
 * It contains RTC, battery monitoring, system power management, and PWM
 * functionality.
 *
 * This driver implements register access, version detection, and system
 * power-off/reset.
 *
 * Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@gmx.net>
 */

#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/i2c.h>
#include <linux/mfd/core.h>
#include <linux/mfd/ntxec.h>
#include <linux/module.h>
#include <linux/pm.h>
#include <linux/reboot.h>
#include <linux/regmap.h>
#include <linux/types.h>
#include <linux/unaligned.h>

#define NTXEC_REG_VERSION       0x00
#define NTXEC_REG_POWEROFF      0x50
#define NTXEC_REG_POWERKEEP     0x70
#define NTXEC_REG_RESET         0x90

#define NTXEC_POWEROFF_VALUE    0x0100
#define NTXEC_POWERKEEP_VALUE   0x0800
#define NTXEC_RESET_VALUE       0xff00

static struct i2c_client *poweroff_restart_client;

static void ntxec_poweroff(void)
{
        int res;
        u8 buf[3] = { NTXEC_REG_POWEROFF };
        struct i2c_msg msgs[] = {
                {
                        .addr = poweroff_restart_client->addr,
                        .flags = 0,
                        .len = sizeof(buf),
                        .buf = buf,
                },
        };

        put_unaligned_be16(NTXEC_POWEROFF_VALUE, buf + 1);

        res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
        if (res < 0)
                dev_warn(&poweroff_restart_client->dev,
                         "Failed to power off (err = %d)\n", res);

        /*
         * The time from the register write until the host CPU is powered off
         * has been observed to be about 2.5 to 3 seconds. Sleep long enough to
         * safely avoid returning from the poweroff handler.
         */
        msleep(5000);
}

static int ntxec_restart(struct notifier_block *nb,
                         unsigned long action, void *data)
{
        int res;
        u8 buf[3] = { NTXEC_REG_RESET };
        /*
         * NOTE: The lower half of the reset value is not sent, because sending
         * it causes an I2C error. (The reset handler in the downstream driver
         * does send the full two-byte value, but doesn't check the result).
         */
        struct i2c_msg msgs[] = {
                {
                        .addr = poweroff_restart_client->addr,
                        .flags = 0,
                        .len = sizeof(buf) - 1,
                        .buf = buf,
                },
        };

        put_unaligned_be16(NTXEC_RESET_VALUE, buf + 1);

        res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
        if (res < 0)
                dev_warn(&poweroff_restart_client->dev,
                         "Failed to restart (err = %d)\n", res);

        return NOTIFY_DONE;
}

static struct notifier_block ntxec_restart_handler = {
        .notifier_call = ntxec_restart,
        .priority = 128,
};

static int regmap_ignore_write(void *context,
                               unsigned int reg, unsigned int val)

{
        struct regmap *regmap = context;

        regmap_write(regmap, reg, val);

        return 0;
}

static int regmap_wrap_read(void *context, unsigned int reg,
                            unsigned int *val)
{
        struct regmap *regmap = context;

        return regmap_read(regmap, reg, val);
}

/*
 * Some firmware versions do not ack written data, add a wrapper. It
 * is used to stack another regmap on top.
 */
static const struct regmap_config regmap_config_noack = {
        .name = "ntxec_noack",
        .reg_bits = 8,
        .val_bits = 16,
        .cache_type = REGCACHE_NONE,
        .reg_write = regmap_ignore_write,
        .reg_read = regmap_wrap_read
};

static const struct regmap_config regmap_config = {
        .name = "ntxec",
        .reg_bits = 8,
        .val_bits = 16,
        .cache_type = REGCACHE_NONE,
        .val_format_endian = REGMAP_ENDIAN_BIG,
};

static const struct mfd_cell ntxec_subdev[] = {
        { .name = "ntxec-rtc" },
        { .name = "ntxec-pwm" },
};

static const struct mfd_cell ntxec_subdev_pwm[] = {
        { .name = "ntxec-pwm" },
};

static int ntxec_probe(struct i2c_client *client)
{
        struct ntxec *ec;
        unsigned int version;
        int res;
        const struct mfd_cell *subdevs;
        size_t n_subdevs;

        ec = devm_kmalloc(&client->dev, sizeof(*ec), GFP_KERNEL);
        if (!ec)
                return -ENOMEM;

        ec->dev = &client->dev;

        ec->regmap = devm_regmap_init_i2c(client, &regmap_config);
        if (IS_ERR(ec->regmap)) {
                dev_err(ec->dev, "Failed to set up regmap for device\n");
                return PTR_ERR(ec->regmap);
        }

        /* Determine the firmware version */
        res = regmap_read(ec->regmap, NTXEC_REG_VERSION, &version);
        if (res < 0) {
                dev_err(ec->dev, "Failed to read firmware version number\n");
                return res;
        }

        /* Bail out if we encounter an unknown firmware version */
        switch (version) {
        case NTXEC_VERSION_KOBO_AURA:
        case NTXEC_VERSION_TOLINO_VISION:
                subdevs = ntxec_subdev;
                n_subdevs = ARRAY_SIZE(ntxec_subdev);
                break;
        case NTXEC_VERSION_TOLINO_SHINE2:
                subdevs = ntxec_subdev_pwm;
                n_subdevs = ARRAY_SIZE(ntxec_subdev_pwm);
                /* Another regmap stacked on top of the other */
                ec->regmap = devm_regmap_init(ec->dev, NULL,
                                              ec->regmap,
                                              &regmap_config_noack);
                if (IS_ERR(ec->regmap))
                        return PTR_ERR(ec->regmap);
                break;
        default:
                dev_err(ec->dev,
                        "Netronix embedded controller version %04x is not supported.\n",
                        version);
                return -ENODEV;
        }

        dev_info(ec->dev,
                 "Netronix embedded controller version %04x detected.\n", version);

        if (of_device_is_system_power_controller(ec->dev->of_node)) {
                /*
                 * Set the 'powerkeep' bit. This is necessary on some boards
                 * in order to keep the system running.
                 */
                res = regmap_write(ec->regmap, NTXEC_REG_POWERKEEP,
                                   NTXEC_POWERKEEP_VALUE);
                if (res < 0)
                        return res;

                if (poweroff_restart_client)
                        /*
                         * Another instance of the driver already took
                         * poweroff/restart duties.
                         */
                        dev_err(ec->dev, "poweroff_restart_client already assigned\n");
                else
                        poweroff_restart_client = client;

                if (pm_power_off)
                        /* Another driver already registered a poweroff handler. */
                        dev_err(ec->dev, "pm_power_off already assigned\n");
                else
                        pm_power_off = ntxec_poweroff;

                res = register_restart_handler(&ntxec_restart_handler);
                if (res)
                        dev_err(ec->dev,
                                "Failed to register restart handler: %d\n", res);
        }

        i2c_set_clientdata(client, ec);

        res = devm_mfd_add_devices(ec->dev, PLATFORM_DEVID_NONE,
                                   subdevs, n_subdevs, NULL, 0, NULL);
        if (res)
                dev_err(ec->dev, "Failed to add subdevices: %d\n", res);

        return res;
}

static void ntxec_remove(struct i2c_client *client)
{
        if (client == poweroff_restart_client) {
                poweroff_restart_client = NULL;
                pm_power_off = NULL;
                unregister_restart_handler(&ntxec_restart_handler);
        }
}

static const struct of_device_id of_ntxec_match_table[] = {
        { .compatible = "netronix,ntxec", },
        {}
};
MODULE_DEVICE_TABLE(of, of_ntxec_match_table);

static struct i2c_driver ntxec_driver = {
        .driver = {
                .name = "ntxec",
                .of_match_table = of_ntxec_match_table,
        },
        .probe = ntxec_probe,
        .remove = ntxec_remove,
};
module_i2c_driver(ntxec_driver);

MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@gmx.net>");
MODULE_DESCRIPTION("Core driver for Netronix EC");
MODULE_LICENSE("GPL");