alistair23-linux/drivers/misc/eeprom/max6875.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * max6875.c - driver for MAX6874/MAX6875
 *
 * Copyright (C) 2005 Ben Gardner <bgardner@wabtec.com>
 *
 * Based on eeprom.c
 *
 * The MAX6875 has a bank of registers and two banks of EEPROM.
 * Address ranges are defined as follows:
 *  * 0x0000 - 0x0046 = configuration registers
 *  * 0x8000 - 0x8046 = configuration EEPROM
 *  * 0x8100 - 0x82FF = user EEPROM
 *
 * This driver makes the user EEPROM available for read.
 *
 * The registers & config EEPROM should be accessed via i2c-dev.
 *
 * The MAX6875 ignores the lowest address bit, so each chip responds to
 * two addresses - 0x50/0x51 and 0x52/0x53.
 *
 * Note that the MAX6875 uses i2c_smbus_write_byte_data() to set the read
 * address, so this driver is destructive if loaded for the wrong EEPROM chip.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/mutex.h>

/* The MAX6875 can only read/write 16 bytes at a time */
#define SLICE_SIZE			16
#define SLICE_BITS			4

/* USER EEPROM is at addresses 0x8100 - 0x82FF */
#define USER_EEPROM_BASE		0x8100
#define USER_EEPROM_SIZE		0x0200
#define USER_EEPROM_SLICES		32

/* MAX6875 commands */
#define MAX6875_CMD_BLK_READ		0x84

/* Each client has this additional data */
struct max6875_data {
	struct i2c_client	*fake_client;
	struct mutex		update_lock;

	u32			valid;
	u8			data[USER_EEPROM_SIZE];
	unsigned long		last_updated[USER_EEPROM_SLICES];
};

static void max6875_update_slice(struct i2c_client *client, int slice)
{
	struct max6875_data *data = i2c_get_clientdata(client);
	int i, j, addr;
	u8 *buf;

	if (slice >= USER_EEPROM_SLICES)
		return;

	mutex_lock(&data->update_lock);

	buf = &data->data[slice << SLICE_BITS];

	if (!(data->valid & (1 << slice)) ||
	    time_after(jiffies, data->last_updated[slice])) {

		dev_dbg(&client->dev, "Starting update of slice %u\n", slice);

		data->valid &= ~(1 << slice);

		addr = USER_EEPROM_BASE + (slice << SLICE_BITS);

		/* select the eeprom address */
		if (i2c_smbus_write_byte_data(client, addr >> 8, addr & 0xFF)) {
			dev_err(&client->dev, "address set failed\n");
			goto exit_up;
		}

		if (i2c_check_functionality(client->adapter,
					    I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
			if (i2c_smbus_read_i2c_block_data(client,
							  MAX6875_CMD_BLK_READ,
							  SLICE_SIZE,
							  buf) != SLICE_SIZE) {
				goto exit_up;
			}
		} else {
			for (i = 0; i < SLICE_SIZE; i++) {
				j = i2c_smbus_read_byte(client);
				if (j < 0) {
					goto exit_up;
				}
				buf[i] = j;
			}
		}
		data->last_updated[slice] = jiffies;
		data->valid |= (1 << slice);
	}
exit_up:
	mutex_unlock(&data->update_lock);
}

static ssize_t max6875_read(struct file *filp, struct kobject *kobj,
			    struct bin_attribute *bin_attr,
			    char *buf, loff_t off, size_t count)
{
	struct i2c_client *client = kobj_to_i2c_client(kobj);
	struct max6875_data *data = i2c_get_clientdata(client);
	int slice, max_slice;

	/* refresh slices which contain requested bytes */
	max_slice = (off + count - 1) >> SLICE_BITS;
	for (slice = (off >> SLICE_BITS); slice <= max_slice; slice++)
		max6875_update_slice(client, slice);

	memcpy(buf, &data->data[off], count);

	return count;
}

static const struct bin_attribute user_eeprom_attr = {
	.attr = {
		.name = "eeprom",
		.mode = S_IRUGO,
	},
	.size = USER_EEPROM_SIZE,
	.read = max6875_read,
};

static int max6875_probe(struct i2c_client *client,
			 const struct i2c_device_id *id)
{
	struct i2c_adapter *adapter = client->adapter;
	struct max6875_data *data;
	int err;

	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WRITE_BYTE_DATA
				     | I2C_FUNC_SMBUS_READ_BYTE))
		return -ENODEV;

	/* Only bind to even addresses */
	if (client->addr & 1)
		return -ENODEV;

	data = kzalloc(sizeof(struct max6875_data), GFP_KERNEL);
	if (!data)
		return -ENOMEM;

	/* A fake client is created on the odd address */
	data->fake_client = i2c_new_dummy_device(client->adapter, client->addr + 1);
	if (IS_ERR(data->fake_client)) {
		err = PTR_ERR(data->fake_client);
		goto exit_kfree;
	}

	/* Init real i2c_client */
	i2c_set_clientdata(client, data);
	mutex_init(&data->update_lock);

	err = sysfs_create_bin_file(&client->dev.kobj, &user_eeprom_attr);
	if (err)
		goto exit_remove_fake;

	return 0;

exit_remove_fake:
	i2c_unregister_device(data->fake_client);
exit_kfree:
	kfree(data);
	return err;
}

static int max6875_remove(struct i2c_client *client)
{
	struct max6875_data *data = i2c_get_clientdata(client);

	i2c_unregister_device(data->fake_client);

	sysfs_remove_bin_file(&client->dev.kobj, &user_eeprom_attr);
	kfree(data);

	return 0;
}

static const struct i2c_device_id max6875_id[] = {
	{ "max6875", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, max6875_id);

static struct i2c_driver max6875_driver = {
	.driver = {
		.name	= "max6875",
	},
	.probe		= max6875_probe,
	.remove		= max6875_remove,
	.id_table	= max6875_id,
};

module_i2c_driver(max6875_driver);

MODULE_AUTHOR("Ben Gardner <bgardner@wabtec.com>");
MODULE_DESCRIPTION("MAX6875 driver");
MODULE_LICENSE("GPL");