// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Driver for Sitronix ST7571 connected via I2C bus.
 *
 * Copyright (C) 2025 Marcus Folkesson <marcus.folkesson@gmail.com>
 */

#include <linux/i2c.h>
#include <linux/module.h>
#include <linux/regmap.h>

#include "st7571.h"

struct st7571_i2c_transport {
        struct i2c_client *client;

        /*
         * Depending on the hardware design, the acknowledge signal may be hard to
         * recognize as a valid logic "0" level.
         * Therefor, ignore NAK if possible to stay compatible with most hardware designs
         * and off-the-shelf panels out there.
         *
         * From section 6.4 MICROPOCESSOR INTERFACE section in the datasheet:
         *
         * "By connecting SDA_OUT to SDA_IN externally, the SDA line becomes fully
         * I2C interface compatible.
         * Separating acknowledge-output from serial data
         * input is advantageous for chip-on-glass (COG) applications. In COG
         * applications, the ITO resistance and the pull-up resistor will form a
         * voltage  divider, which affects acknowledge-signal level. Larger ITO
         * resistance will raise the acknowledged-signal level and system cannot
         * recognize this level as a valid logic “0” level. By separating SDA_IN from
         * SDA_OUT, the IC can be used in a mode that ignores the acknowledge-bit.
         * For applications which check acknowledge-bit, it is necessary to minimize
         * the ITO resistance of the SDA_OUT trace to guarantee a valid low level."
         *
         */
        bool ignore_nak;
};

static int st7571_i2c_regmap_write(void *context, const void *data, size_t count)
{
        struct st7571_i2c_transport *t = context;
        int ret;

        struct i2c_msg msg = {
                .addr = t->client->addr,
                .flags = t->ignore_nak ? I2C_M_IGNORE_NAK : 0,
                .len = count,
                .buf = (u8 *)data
        };

        ret = i2c_transfer(t->client->adapter, &msg, 1);

        /*
         * Unfortunately, there is no way to check if the transfer failed because of
         * a NAK or something else as I2C bus drivers use different return values for NAK.
         *
         * However, if the transfer fails and ignore_nak is set, we know it is an error.
         */
        if (ret < 0 && t->ignore_nak)
                return ret;

        return 0;
}

/* The st7571 driver does not read registers but regmap expects a .read */
static int st7571_i2c_regmap_read(void *context, const void *reg_buf,
                                  size_t reg_size, void *val_buf, size_t val_size)
{
        return -EOPNOTSUPP;
}

static const struct regmap_bus st7571_i2c_regmap_bus = {
        .read = st7571_i2c_regmap_read,
        .write = st7571_i2c_regmap_write,
};

static const struct regmap_config st7571_i2c_regmap_config = {
        .reg_bits = 8,
        .val_bits = 8,
        .use_single_write = true,
};

static int st7571_i2c_probe(struct i2c_client *client)
{
        struct st7571_device *st7571;
        struct st7571_i2c_transport *t;
        struct regmap *regmap;

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

        t->client = client;

        /*
         * The hardware design could make it hard to detect a NAK on the I2C bus.
         * If the adapter does not support protocol mangling do
         * not set the I2C_M_IGNORE_NAK flag at the expense * of possible
         * cruft in the logs.
         */
        if (i2c_check_functionality(client->adapter, I2C_FUNC_PROTOCOL_MANGLING))
                t->ignore_nak = true;

        regmap = devm_regmap_init(&client->dev, &st7571_i2c_regmap_bus,
                                  t, &st7571_i2c_regmap_config);
        if (IS_ERR(regmap)) {
                return dev_err_probe(&client->dev, PTR_ERR(regmap),
                                     "Failed to initialize regmap\n");
        }

        st7571 = st7571_probe(&client->dev, regmap);
        if (IS_ERR(st7571))
                return dev_err_probe(&client->dev, PTR_ERR(st7571),
                                     "Failed to initialize regmap\n");

        i2c_set_clientdata(client, st7571);
        return 0;
}

static void st7571_i2c_remove(struct i2c_client *client)
{
        struct st7571_device *st7571 = i2c_get_clientdata(client);

        st7571_remove(st7571);
}

static const struct of_device_id st7571_of_match[] = {
        { .compatible = "sitronix,st7567", .data = &st7567_config },
        { .compatible = "sitronix,st7571", .data = &st7571_config },
        {},
};
MODULE_DEVICE_TABLE(of, st7571_of_match);

static const struct i2c_device_id st7571_id[] = {
        { "st7567", 0 },
        { "st7571", 0 },
        { }
};
MODULE_DEVICE_TABLE(i2c, st7571_id);

static struct i2c_driver st7571_i2c_driver = {
        .driver = {
                .name = "st7571-i2c",
                .of_match_table = st7571_of_match,
        },
        .probe = st7571_i2c_probe,
        .remove = st7571_i2c_remove,
        .id_table = st7571_id,
};

module_i2c_driver(st7571_i2c_driver);

MODULE_AUTHOR("Marcus Folkesson <marcus.folkesson@gmail.com>");
MODULE_DESCRIPTION("DRM Driver for Sitronix ST7571 LCD controller (I2C)");
MODULE_LICENSE("GPL");
MODULE_IMPORT_NS("DRM_ST7571");