1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * I2C slave mode EEPROM simulator
4 *
5 * Copyright (C) 2014 by Wolfram Sang, Sang Engineering <wsa@sang-engineering.com>
6 * Copyright (C) 2014 by Renesas Electronics Corporation
7 *
8 * Because most slave IP cores can only detect one I2C slave address anyhow,
9 * this driver does not support simulating EEPROM types which take more than
10 * one address.
11 */
12
13/*
14 * FIXME: What to do if only 8 bits of a 16 bit address are sent?
15 * The ST-M24C64 sends only 0xff then. Needs verification with other
16 * EEPROMs, though. We currently use the 8 bit as a valid address.
17 */
18
19#include <linux/bitfield.h>
20#include <linux/firmware.h>
21#include <linux/i2c.h>
22#include <linux/init.h>
23#include <linux/module.h>
24#include <linux/of.h>
25#include <linux/slab.h>
26#include <linux/spinlock.h>
27#include <linux/sysfs.h>
28
29struct eeprom_data {
30	struct bin_attribute bin;
31	spinlock_t buffer_lock;
32	u16 buffer_idx;
33	u16 address_mask;
34	u8 num_address_bytes;
35	u8 idx_write_cnt;
36	bool read_only;
37	u8 buffer[];
38};
39
40#define I2C_SLAVE_BYTELEN GENMASK(15, 0)
41#define I2C_SLAVE_FLAG_ADDR16 BIT(16)
42#define I2C_SLAVE_FLAG_RO BIT(17)
43#define I2C_SLAVE_DEVICE_MAGIC(_len, _flags) ((_flags) | ((_len) - 1))
44
45static int i2c_slave_eeprom_slave_cb(struct i2c_client *client,
46				     enum i2c_slave_event event, u8 *val)
47{
48	struct eeprom_data *eeprom = i2c_get_clientdata(client);
49
50	switch (event) {
51	case I2C_SLAVE_WRITE_RECEIVED:
52		if (eeprom->idx_write_cnt < eeprom->num_address_bytes) {
53			if (eeprom->idx_write_cnt == 0)
54				eeprom->buffer_idx = 0;
55			eeprom->buffer_idx = *val | (eeprom->buffer_idx << 8);
56			eeprom->idx_write_cnt++;
57		} else {
58			if (!eeprom->read_only) {
59				spin_lock(&eeprom->buffer_lock);
60				eeprom->buffer[eeprom->buffer_idx++ & eeprom->address_mask] = *val;
61				spin_unlock(&eeprom->buffer_lock);
62			}
63		}
64		break;
65
66	case I2C_SLAVE_READ_PROCESSED:
67		/* The previous byte made it to the bus, get next one */
68		eeprom->buffer_idx++;
69		fallthrough;
70	case I2C_SLAVE_READ_REQUESTED:
71		spin_lock(&eeprom->buffer_lock);
72		*val = eeprom->buffer[eeprom->buffer_idx & eeprom->address_mask];
73		spin_unlock(&eeprom->buffer_lock);
74		/*
75		 * Do not increment buffer_idx here, because we don't know if
76		 * this byte will be actually used. Read Linux I2C slave docs
77		 * for details.
78		 */
79		break;
80
81	case I2C_SLAVE_STOP:
82	case I2C_SLAVE_WRITE_REQUESTED:
83		eeprom->idx_write_cnt = 0;
84		break;
85
86	default:
87		break;
88	}
89
90	return 0;
91}
92
93static ssize_t i2c_slave_eeprom_bin_read(struct file *filp, struct kobject *kobj,
94		struct bin_attribute *attr, char *buf, loff_t off, size_t count)
95{
96	struct eeprom_data *eeprom;
97	unsigned long flags;
98
99	eeprom = dev_get_drvdata(kobj_to_dev(kobj));
100
101	spin_lock_irqsave(&eeprom->buffer_lock, flags);
102	memcpy(buf, &eeprom->buffer[off], count);
103	spin_unlock_irqrestore(&eeprom->buffer_lock, flags);
104
105	return count;
106}
107
108static ssize_t i2c_slave_eeprom_bin_write(struct file *filp, struct kobject *kobj,
109		struct bin_attribute *attr, char *buf, loff_t off, size_t count)
110{
111	struct eeprom_data *eeprom;
112	unsigned long flags;
113
114	eeprom = dev_get_drvdata(kobj_to_dev(kobj));
115
116	spin_lock_irqsave(&eeprom->buffer_lock, flags);
117	memcpy(&eeprom->buffer[off], buf, count);
118	spin_unlock_irqrestore(&eeprom->buffer_lock, flags);
119
120	return count;
121}
122
123static int i2c_slave_init_eeprom_data(struct eeprom_data *eeprom, struct i2c_client *client,
124				      unsigned int size)
125{
126	const struct firmware *fw;
127	const char *eeprom_data;
128	int ret = device_property_read_string(&client->dev, "firmware-name", &eeprom_data);
129
130	if (!ret) {
131		ret = request_firmware_into_buf(&fw, eeprom_data, &client->dev,
132						eeprom->buffer, size);
133		if (ret)
134			return ret;
135		release_firmware(fw);
136	} else {
137		/* An empty eeprom typically has all bits set to 1 */
138		memset(eeprom->buffer, 0xff, size);
139	}
140	return 0;
141}
142
143static int i2c_slave_eeprom_probe(struct i2c_client *client)
144{
145	const struct i2c_device_id *id = i2c_client_get_device_id(client);
146	struct eeprom_data *eeprom;
147	int ret;
148	unsigned int size = FIELD_GET(I2C_SLAVE_BYTELEN, id->driver_data) + 1;
149	unsigned int flag_addr16 = FIELD_GET(I2C_SLAVE_FLAG_ADDR16, id->driver_data);
150
151	eeprom = devm_kzalloc(&client->dev, sizeof(struct eeprom_data) + size, GFP_KERNEL);
152	if (!eeprom)
153		return -ENOMEM;
154
155	eeprom->num_address_bytes = flag_addr16 ? 2 : 1;
156	eeprom->address_mask = size - 1;
157	eeprom->read_only = FIELD_GET(I2C_SLAVE_FLAG_RO, id->driver_data);
158	spin_lock_init(&eeprom->buffer_lock);
159	i2c_set_clientdata(client, eeprom);
160
161	ret = i2c_slave_init_eeprom_data(eeprom, client, size);
162	if (ret)
163		return ret;
164
165	sysfs_bin_attr_init(&eeprom->bin);
166	eeprom->bin.attr.name = "slave-eeprom";
167	eeprom->bin.attr.mode = S_IRUSR | S_IWUSR;
168	eeprom->bin.read = i2c_slave_eeprom_bin_read;
169	eeprom->bin.write = i2c_slave_eeprom_bin_write;
170	eeprom->bin.size = size;
171
172	ret = sysfs_create_bin_file(&client->dev.kobj, &eeprom->bin);
173	if (ret)
174		return ret;
175
176	ret = i2c_slave_register(client, i2c_slave_eeprom_slave_cb);
177	if (ret) {
178		sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
179		return ret;
180	}
181
182	return 0;
183};
184
185static void i2c_slave_eeprom_remove(struct i2c_client *client)
186{
187	struct eeprom_data *eeprom = i2c_get_clientdata(client);
188
189	i2c_slave_unregister(client);
190	sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
191}
192
193static const struct i2c_device_id i2c_slave_eeprom_id[] = {
194	{ "slave-24c02", I2C_SLAVE_DEVICE_MAGIC(2048 / 8,  0) },
195	{ "slave-24c02ro", I2C_SLAVE_DEVICE_MAGIC(2048 / 8,  I2C_SLAVE_FLAG_RO) },
196	{ "slave-24c32", I2C_SLAVE_DEVICE_MAGIC(32768 / 8, I2C_SLAVE_FLAG_ADDR16) },
197	{ "slave-24c32ro", I2C_SLAVE_DEVICE_MAGIC(32768 / 8, I2C_SLAVE_FLAG_ADDR16 | I2C_SLAVE_FLAG_RO) },
198	{ "slave-24c64", I2C_SLAVE_DEVICE_MAGIC(65536 / 8, I2C_SLAVE_FLAG_ADDR16) },
199	{ "slave-24c64ro", I2C_SLAVE_DEVICE_MAGIC(65536 / 8, I2C_SLAVE_FLAG_ADDR16 | I2C_SLAVE_FLAG_RO) },
200	{ "slave-24c512", I2C_SLAVE_DEVICE_MAGIC(524288 / 8, I2C_SLAVE_FLAG_ADDR16) },
201	{ "slave-24c512ro", I2C_SLAVE_DEVICE_MAGIC(524288 / 8, I2C_SLAVE_FLAG_ADDR16 | I2C_SLAVE_FLAG_RO) },
202	{ }
203};
204MODULE_DEVICE_TABLE(i2c, i2c_slave_eeprom_id);
205
206static struct i2c_driver i2c_slave_eeprom_driver = {
207	.driver = {
208		.name = "i2c-slave-eeprom",
209	},
210	.probe = i2c_slave_eeprom_probe,
211	.remove = i2c_slave_eeprom_remove,
212	.id_table = i2c_slave_eeprom_id,
213};
214module_i2c_driver(i2c_slave_eeprom_driver);
215
216MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
217MODULE_DESCRIPTION("I2C slave mode EEPROM simulator");
218MODULE_LICENSE("GPL v2");
219