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 IP blocks can only detect one I2C slave address anyhow, this
9  * driver does not support simulating EEPROM types which take more than one
10  * address. It is prepared to simulate bigger EEPROMs with an internal 16 bit
11  * pointer, yet implementation is deferred until the need actually arises.
12  */
13 
14 /*
15  * FIXME: What to do if only 8 bits of a 16 bit address are sent?
16  * The ST-M24C64 sends only 0xff then. Needs verification with other
17  * EEPROMs, though. We currently use the 8 bit as a valid address.
18  */
19 
20 #include <linux/bitfield.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))
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(container_of(kobj, struct device, 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(container_of(kobj, struct device, 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_eeprom_probe(struct i2c_client *client, const struct i2c_device_id *id)
124 {
125 	struct eeprom_data *eeprom;
126 	int ret;
127 	unsigned int size = FIELD_GET(I2C_SLAVE_BYTELEN, id->driver_data);
128 	unsigned int flag_addr16 = FIELD_GET(I2C_SLAVE_FLAG_ADDR16, id->driver_data);
129 
130 	eeprom = devm_kzalloc(&client->dev, sizeof(struct eeprom_data) + size, GFP_KERNEL);
131 	if (!eeprom)
132 		return -ENOMEM;
133 
134 	eeprom->idx_write_cnt = 0;
135 	eeprom->num_address_bytes = flag_addr16 ? 2 : 1;
136 	eeprom->address_mask = size - 1;
137 	eeprom->read_only = FIELD_GET(I2C_SLAVE_FLAG_RO, id->driver_data);
138 	spin_lock_init(&eeprom->buffer_lock);
139 	i2c_set_clientdata(client, eeprom);
140 
141 	sysfs_bin_attr_init(&eeprom->bin);
142 	eeprom->bin.attr.name = "slave-eeprom";
143 	eeprom->bin.attr.mode = S_IRUSR | S_IWUSR;
144 	eeprom->bin.read = i2c_slave_eeprom_bin_read;
145 	eeprom->bin.write = i2c_slave_eeprom_bin_write;
146 	eeprom->bin.size = size;
147 
148 	ret = sysfs_create_bin_file(&client->dev.kobj, &eeprom->bin);
149 	if (ret)
150 		return ret;
151 
152 	ret = i2c_slave_register(client, i2c_slave_eeprom_slave_cb);
153 	if (ret) {
154 		sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
155 		return ret;
156 	}
157 
158 	return 0;
159 };
160 
161 static int i2c_slave_eeprom_remove(struct i2c_client *client)
162 {
163 	struct eeprom_data *eeprom = i2c_get_clientdata(client);
164 
165 	i2c_slave_unregister(client);
166 	sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
167 
168 	return 0;
169 }
170 
171 static const struct i2c_device_id i2c_slave_eeprom_id[] = {
172 	{ "slave-24c02", I2C_SLAVE_DEVICE_MAGIC(2048 / 8,  0) },
173 	{ "slave-24c02ro", I2C_SLAVE_DEVICE_MAGIC(2048 / 8,  I2C_SLAVE_FLAG_RO) },
174 	{ "slave-24c32", I2C_SLAVE_DEVICE_MAGIC(32768 / 8, I2C_SLAVE_FLAG_ADDR16) },
175 	{ "slave-24c32ro", I2C_SLAVE_DEVICE_MAGIC(32768 / 8, I2C_SLAVE_FLAG_ADDR16 | I2C_SLAVE_FLAG_RO) },
176 	{ "slave-24c64", I2C_SLAVE_DEVICE_MAGIC(65536 / 8, I2C_SLAVE_FLAG_ADDR16) },
177 	{ "slave-24c64ro", I2C_SLAVE_DEVICE_MAGIC(65536 / 8, I2C_SLAVE_FLAG_ADDR16 | I2C_SLAVE_FLAG_RO) },
178 	{ }
179 };
180 MODULE_DEVICE_TABLE(i2c, i2c_slave_eeprom_id);
181 
182 static struct i2c_driver i2c_slave_eeprom_driver = {
183 	.driver = {
184 		.name = "i2c-slave-eeprom",
185 	},
186 	.probe = i2c_slave_eeprom_probe,
187 	.remove = i2c_slave_eeprom_remove,
188 	.id_table = i2c_slave_eeprom_id,
189 };
190 module_i2c_driver(i2c_slave_eeprom_driver);
191 
192 MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
193 MODULE_DESCRIPTION("I2C slave mode EEPROM simulator");
194 MODULE_LICENSE("GPL v2");
195