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 
29 struct 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 
45 static 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 
93 static 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 
108 static 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 
123 static 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 
143 static 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 
185 static 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 
193 static 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 };
204 MODULE_DEVICE_TABLE(i2c, i2c_slave_eeprom_id);
205 
206 static struct i2c_driver i2c_slave_eeprom_driver = {
207 	.driver = {
208 		.name = "i2c-slave-eeprom",
209 	},
210 	.probe_new = i2c_slave_eeprom_probe,
211 	.remove = i2c_slave_eeprom_remove,
212 	.id_table = i2c_slave_eeprom_id,
213 };
214 module_i2c_driver(i2c_slave_eeprom_driver);
215 
216 MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
217 MODULE_DESCRIPTION("I2C slave mode EEPROM simulator");
218 MODULE_LICENSE("GPL v2");
219