// SPDX-License-Identifier: GPL-2.0-only
/*
 * I2C slave mode EEPROM simulator
 *
 * Copyright (C) 2014 by Wolfram Sang, Sang Engineering <wsa@sang-engineering.com>
 * Copyright (C) 2014 by Renesas Electronics Corporation
 *
 * Because most slave IP cores can only detect one I2C slave address anyhow,
 * this driver does not support simulating EEPROM types which take more than
 * one address.
 */

/*
 * FIXME: What to do if only 8 bits of a 16 bit address are sent?
 * The ST-M24C64 sends only 0xff then. Needs verification with other
 * EEPROMs, though. We currently use the 8 bit as a valid address.
 */

#include <linux/bitfield.h>
#include <linux/firmware.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/sysfs.h>

struct eeprom_data {
        struct bin_attribute bin;
        spinlock_t buffer_lock;
        u16 buffer_idx;
        u16 address_mask;
        u8 num_address_bytes;
        u8 idx_write_cnt;
        bool read_only;
        u8 buffer[];
};

#define I2C_SLAVE_BYTELEN GENMASK(15, 0)
#define I2C_SLAVE_FLAG_ADDR16 BIT(16)
#define I2C_SLAVE_FLAG_RO BIT(17)
#define I2C_SLAVE_DEVICE_MAGIC(_len, _flags) ((_flags) | ((_len) - 1))

static int i2c_slave_eeprom_slave_cb(struct i2c_client *client,
                                     enum i2c_slave_event event, u8 *val)
{
        struct eeprom_data *eeprom = i2c_get_clientdata(client);

        switch (event) {
        case I2C_SLAVE_WRITE_RECEIVED:
                if (eeprom->idx_write_cnt < eeprom->num_address_bytes) {
                        if (eeprom->idx_write_cnt == 0)
                                eeprom->buffer_idx = 0;
                        eeprom->buffer_idx = *val | (eeprom->buffer_idx << 8);
                        eeprom->idx_write_cnt++;
                } else {
                        if (!eeprom->read_only) {
                                spin_lock(&eeprom->buffer_lock);
                                eeprom->buffer[eeprom->buffer_idx++ & eeprom->address_mask] = *val;
                                spin_unlock(&eeprom->buffer_lock);
                        }
                }
                break;

        case I2C_SLAVE_READ_PROCESSED:
                /* The previous byte made it to the bus, get next one */
                eeprom->buffer_idx++;
                fallthrough;
        case I2C_SLAVE_READ_REQUESTED:
                spin_lock(&eeprom->buffer_lock);
                *val = eeprom->buffer[eeprom->buffer_idx & eeprom->address_mask];
                spin_unlock(&eeprom->buffer_lock);
                /*
                 * Do not increment buffer_idx here, because we don't know if
                 * this byte will be actually used. Read Linux I2C slave docs
                 * for details.
                 */
                break;

        case I2C_SLAVE_STOP:
        case I2C_SLAVE_WRITE_REQUESTED:
                eeprom->idx_write_cnt = 0;
                break;

        default:
                break;
        }

        return 0;
}

static ssize_t i2c_slave_eeprom_bin_read(struct file *filp, struct kobject *kobj,
                const struct bin_attribute *attr, char *buf, loff_t off, size_t count)
{
        struct eeprom_data *eeprom;
        unsigned long flags;

        eeprom = dev_get_drvdata(kobj_to_dev(kobj));

        spin_lock_irqsave(&eeprom->buffer_lock, flags);
        memcpy(buf, &eeprom->buffer[off], count);
        spin_unlock_irqrestore(&eeprom->buffer_lock, flags);

        return count;
}

static ssize_t i2c_slave_eeprom_bin_write(struct file *filp, struct kobject *kobj,
                const struct bin_attribute *attr, char *buf, loff_t off, size_t count)
{
        struct eeprom_data *eeprom;
        unsigned long flags;

        eeprom = dev_get_drvdata(kobj_to_dev(kobj));

        spin_lock_irqsave(&eeprom->buffer_lock, flags);
        memcpy(&eeprom->buffer[off], buf, count);
        spin_unlock_irqrestore(&eeprom->buffer_lock, flags);

        return count;
}

static int i2c_slave_init_eeprom_data(struct eeprom_data *eeprom, struct i2c_client *client,
                                      unsigned int size)
{
        const struct firmware *fw;
        const char *eeprom_data;
        int ret = device_property_read_string(&client->dev, "firmware-name", &eeprom_data);

        if (!ret) {
                ret = request_firmware_into_buf(&fw, eeprom_data, &client->dev,
                                                eeprom->buffer, size);
                if (ret)
                        return ret;
                release_firmware(fw);
        } else {
                /* An empty eeprom typically has all bits set to 1 */
                memset(eeprom->buffer, 0xff, size);
        }
        return 0;
}

static int i2c_slave_eeprom_probe(struct i2c_client *client)
{
        const struct i2c_device_id *id = i2c_client_get_device_id(client);
        struct eeprom_data *eeprom;
        int ret;
        unsigned int size = FIELD_GET(I2C_SLAVE_BYTELEN, id->driver_data) + 1;
        unsigned int flag_addr16 = FIELD_GET(I2C_SLAVE_FLAG_ADDR16, id->driver_data);

        eeprom = devm_kzalloc(&client->dev, sizeof(struct eeprom_data) + size, GFP_KERNEL);
        if (!eeprom)
                return -ENOMEM;

        eeprom->num_address_bytes = flag_addr16 ? 2 : 1;
        eeprom->address_mask = size - 1;
        eeprom->read_only = FIELD_GET(I2C_SLAVE_FLAG_RO, id->driver_data);
        spin_lock_init(&eeprom->buffer_lock);
        i2c_set_clientdata(client, eeprom);

        ret = i2c_slave_init_eeprom_data(eeprom, client, size);
        if (ret)
                return ret;

        sysfs_bin_attr_init(&eeprom->bin);
        eeprom->bin.attr.name = "slave-eeprom";
        eeprom->bin.attr.mode = S_IRUSR | S_IWUSR;
        eeprom->bin.read = i2c_slave_eeprom_bin_read;
        eeprom->bin.write = i2c_slave_eeprom_bin_write;
        eeprom->bin.size = size;

        ret = sysfs_create_bin_file(&client->dev.kobj, &eeprom->bin);
        if (ret)
                return ret;

        ret = i2c_slave_register(client, i2c_slave_eeprom_slave_cb);
        if (ret) {
                sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
                return ret;
        }

        return 0;
};

static void i2c_slave_eeprom_remove(struct i2c_client *client)
{
        struct eeprom_data *eeprom = i2c_get_clientdata(client);

        i2c_slave_unregister(client);
        sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
}

static const struct i2c_device_id i2c_slave_eeprom_id[] = {
        { "slave-24c02", I2C_SLAVE_DEVICE_MAGIC(2048 / 8,  0) },
        { "slave-24c02ro", I2C_SLAVE_DEVICE_MAGIC(2048 / 8,  I2C_SLAVE_FLAG_RO) },
        { "slave-24c32", I2C_SLAVE_DEVICE_MAGIC(32768 / 8, I2C_SLAVE_FLAG_ADDR16) },
        { "slave-24c32ro", I2C_SLAVE_DEVICE_MAGIC(32768 / 8, I2C_SLAVE_FLAG_ADDR16 | I2C_SLAVE_FLAG_RO) },
        { "slave-24c64", I2C_SLAVE_DEVICE_MAGIC(65536 / 8, I2C_SLAVE_FLAG_ADDR16) },
        { "slave-24c64ro", I2C_SLAVE_DEVICE_MAGIC(65536 / 8, I2C_SLAVE_FLAG_ADDR16 | I2C_SLAVE_FLAG_RO) },
        { "slave-24c512", I2C_SLAVE_DEVICE_MAGIC(524288 / 8, I2C_SLAVE_FLAG_ADDR16) },
        { "slave-24c512ro", I2C_SLAVE_DEVICE_MAGIC(524288 / 8, I2C_SLAVE_FLAG_ADDR16 | I2C_SLAVE_FLAG_RO) },
        { }
};
MODULE_DEVICE_TABLE(i2c, i2c_slave_eeprom_id);

static struct i2c_driver i2c_slave_eeprom_driver = {
        .driver = {
                .name = "i2c-slave-eeprom",
        },
        .probe = i2c_slave_eeprom_probe,
        .remove = i2c_slave_eeprom_remove,
        .id_table = i2c_slave_eeprom_id,
};
module_i2c_driver(i2c_slave_eeprom_driver);

MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
MODULE_DESCRIPTION("I2C slave mode EEPROM simulator");
MODULE_LICENSE("GPL v2");