1/*
  2 * I2C slave mode EEPROM simulator
  3 *
  4 * Copyright (C) 2014 by Wolfram Sang, Sang Engineering <wsa@sang-engineering.com>
  5 * Copyright (C) 2014 by Renesas Electronics Corporation
  6 *
  7 * This program is free software; you can redistribute it and/or modify it
  8 * under the terms of the GNU General Public License as published by the
  9 * Free Software Foundation; version 2 of the License.
 10 *
 11 * Because most IP blocks can only detect one I2C slave address anyhow, this
 12 * driver does not support simulating EEPROM types which take more than one
 13 * address. It is prepared to simulate bigger EEPROMs with an internal 16 bit
 14 * pointer, yet implementation is deferred until the need actually arises.
 15 */
 16
 17#include <linux/i2c.h>
 18#include <linux/init.h>
 19#include <linux/module.h>
 20#include <linux/of.h>
 21#include <linux/slab.h>
 22#include <linux/spinlock.h>
 23#include <linux/sysfs.h>
 24
 25struct eeprom_data {
 26	struct bin_attribute bin;
 27	bool first_write;
 28	spinlock_t buffer_lock;
 29	u8 buffer_idx;
 30	u8 buffer[];
 31};
 32
 33static int i2c_slave_eeprom_slave_cb(struct i2c_client *client,
 34				     enum i2c_slave_event event, u8 *val)
 35{
 36	struct eeprom_data *eeprom = i2c_get_clientdata(client);
 37
 38	switch (event) {
 39	case I2C_SLAVE_WRITE_RECEIVED:
 40		if (eeprom->first_write) {
 41			eeprom->buffer_idx = *val;
 42			eeprom->first_write = false;
 43		} else {
 44			spin_lock(&eeprom->buffer_lock);
 45			eeprom->buffer[eeprom->buffer_idx++] = *val;
 46			spin_unlock(&eeprom->buffer_lock);
 47		}
 48		break;
 49
 50	case I2C_SLAVE_READ_PROCESSED:
 51		/* The previous byte made it to the bus, get next one */
 52		eeprom->buffer_idx++;
 53		/* fallthrough */
 54	case I2C_SLAVE_READ_REQUESTED:
 55		spin_lock(&eeprom->buffer_lock);
 56		*val = eeprom->buffer[eeprom->buffer_idx];
 57		spin_unlock(&eeprom->buffer_lock);
 58		/*
 59		 * Do not increment buffer_idx here, because we don't know if
 60		 * this byte will be actually used. Read Linux I2C slave docs
 61		 * for details.
 62		 */
 63		break;
 64
 65	case I2C_SLAVE_STOP:
 66	case I2C_SLAVE_WRITE_REQUESTED:
 67		eeprom->first_write = true;
 68		break;
 69
 70	default:
 71		break;
 72	}
 73
 74	return 0;
 75}
 76
 77static ssize_t i2c_slave_eeprom_bin_read(struct file *filp, struct kobject *kobj,
 78		struct bin_attribute *attr, char *buf, loff_t off, size_t count)
 79{
 80	struct eeprom_data *eeprom;
 81	unsigned long flags;
 82
 83	eeprom = dev_get_drvdata(container_of(kobj, struct device, kobj));
 84
 85	spin_lock_irqsave(&eeprom->buffer_lock, flags);
 86	memcpy(buf, &eeprom->buffer[off], count);
 87	spin_unlock_irqrestore(&eeprom->buffer_lock, flags);
 88
 89	return count;
 90}
 91
 92static ssize_t i2c_slave_eeprom_bin_write(struct file *filp, struct kobject *kobj,
 93		struct bin_attribute *attr, char *buf, loff_t off, size_t count)
 94{
 95	struct eeprom_data *eeprom;
 96	unsigned long flags;
 97
 98	eeprom = dev_get_drvdata(container_of(kobj, struct device, kobj));
 99
100	spin_lock_irqsave(&eeprom->buffer_lock, flags);
101	memcpy(&eeprom->buffer[off], buf, count);
102	spin_unlock_irqrestore(&eeprom->buffer_lock, flags);
103
104	return count;
105}
106
107static int i2c_slave_eeprom_probe(struct i2c_client *client, const struct i2c_device_id *id)
108{
109	struct eeprom_data *eeprom;
110	int ret;
111	unsigned size = id->driver_data;
112
113	eeprom = devm_kzalloc(&client->dev, sizeof(struct eeprom_data) + size, GFP_KERNEL);
114	if (!eeprom)
115		return -ENOMEM;
116
117	eeprom->first_write = true;
118	spin_lock_init(&eeprom->buffer_lock);
119	i2c_set_clientdata(client, eeprom);
120
121	sysfs_bin_attr_init(&eeprom->bin);
122	eeprom->bin.attr.name = "slave-eeprom";
123	eeprom->bin.attr.mode = S_IRUSR | S_IWUSR;
124	eeprom->bin.read = i2c_slave_eeprom_bin_read;
125	eeprom->bin.write = i2c_slave_eeprom_bin_write;
126	eeprom->bin.size = size;
127
128	ret = sysfs_create_bin_file(&client->dev.kobj, &eeprom->bin);
129	if (ret)
130		return ret;
131
132	ret = i2c_slave_register(client, i2c_slave_eeprom_slave_cb);
133	if (ret) {
134		sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
135		return ret;
136	}
137
138	return 0;
139};
140
141static int i2c_slave_eeprom_remove(struct i2c_client *client)
142{
143	struct eeprom_data *eeprom = i2c_get_clientdata(client);
144
145	i2c_slave_unregister(client);
146	sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
147
148	return 0;
149}
150
151static const struct i2c_device_id i2c_slave_eeprom_id[] = {
152	{ "slave-24c02", 2048 / 8 },
153	{ }
154};
155MODULE_DEVICE_TABLE(i2c, i2c_slave_eeprom_id);
156
157static struct i2c_driver i2c_slave_eeprom_driver = {
158	.driver = {
159		.name = "i2c-slave-eeprom",
160	},
161	.probe = i2c_slave_eeprom_probe,
162	.remove = i2c_slave_eeprom_remove,
163	.id_table = i2c_slave_eeprom_id,
164};
165module_i2c_driver(i2c_slave_eeprom_driver);
166
167MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
168MODULE_DESCRIPTION("I2C slave mode EEPROM simulator");
169MODULE_LICENSE("GPL v2");