summaryrefslogtreecommitdiff
path: root/drivers/misc/eeprom/ee1004.c
blob: 9fbfe784d71015aeaee46adaa57c2ecfaf96e077 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * ee1004 - driver for DDR4 SPD EEPROMs
 *
 * Copyright (C) 2017-2019 Jean Delvare
 *
 * Based on the at24 driver:
 * Copyright (C) 2005-2007 David Brownell
 * Copyright (C) 2008 Wolfram Sang, Pengutronix
 */

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

/*
 * DDR4 memory modules use special EEPROMs following the Jedec EE1004
 * specification. These are 512-byte EEPROMs using a single I2C address
 * in the 0x50-0x57 range for data. One of two 256-byte page is selected
 * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
 *
 * Therefore we need to request these 2 additional addresses, and serialize
 * access to all such EEPROMs with a single mutex.
 *
 * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
 * We use SMBus access even if I2C is available, these EEPROMs are small
 * enough, and reading from them infrequent enough, that we favor simplicity
 * over performance.
 */

#define EE1004_ADDR_SET_PAGE		0x36
#define EE1004_NUM_PAGES		2
#define EE1004_PAGE_SIZE		256
#define EE1004_PAGE_SHIFT		8
#define EE1004_EEPROM_SIZE		(EE1004_PAGE_SIZE * EE1004_NUM_PAGES)

/*
 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
 * from page selection to end of read.
 */
static DEFINE_MUTEX(ee1004_bus_lock);
static struct i2c_client *ee1004_set_page[EE1004_NUM_PAGES];
static unsigned int ee1004_dev_count;
static int ee1004_current_page;

static const struct i2c_device_id ee1004_ids[] = {
	{ "ee1004", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, ee1004_ids);

/*-------------------------------------------------------------------------*/

static int ee1004_get_current_page(void)
{
	int err;

	err = i2c_smbus_read_byte(ee1004_set_page[0]);
	if (err == -ENXIO) {
		/* Nack means page 1 is selected */
		return 1;
	}
	if (err < 0) {
		/* Anything else is a real error, bail out */
		return err;
	}

	/* Ack means page 0 is selected, returned value meaningless */
	return 0;
}

static int ee1004_set_current_page(struct device *dev, int page)
{
	int ret;

	if (page == ee1004_current_page)
		return 0;

	/* Data is ignored */
	ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00);
	/*
	 * Don't give up just yet. Some memory modules will select the page
	 * but not ack the command. Check which page is selected now.
	 */
	if (ret == -ENXIO && ee1004_get_current_page() == page)
		ret = 0;
	if (ret < 0) {
		dev_err(dev, "Failed to select page %d (%d)\n", page, ret);
		return ret;
	}

	dev_dbg(dev, "Selected page %d\n", page);
	ee1004_current_page = page;

	return 0;
}

static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
				  unsigned int offset, size_t count)
{
	int status, page;

	page = offset >> EE1004_PAGE_SHIFT;
	offset &= (1 << EE1004_PAGE_SHIFT) - 1;

	status = ee1004_set_current_page(&client->dev, page);
	if (status)
		return status;

	/* Can't cross page boundaries */
	if (offset + count > EE1004_PAGE_SIZE)
		count = EE1004_PAGE_SIZE - offset;

	if (count > I2C_SMBUS_BLOCK_MAX)
		count = I2C_SMBUS_BLOCK_MAX;

	return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
}

static ssize_t eeprom_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);
	size_t requested = count;
	int ret = 0;

	/*
	 * Read data from chip, protecting against concurrent access to
	 * other EE1004 SPD EEPROMs on the same adapter.
	 */
	mutex_lock(&ee1004_bus_lock);

	while (count) {
		ret = ee1004_eeprom_read(client, buf, off, count);
		if (ret < 0)
			goto out;

		buf += ret;
		off += ret;
		count -= ret;
	}
out:
	mutex_unlock(&ee1004_bus_lock);

	return ret < 0 ? ret : requested;
}

static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);

static struct bin_attribute *ee1004_attrs[] = {
	&bin_attr_eeprom,
	NULL
};

BIN_ATTRIBUTE_GROUPS(ee1004);

static void ee1004_cleanup(int idx)
{
	if (--ee1004_dev_count == 0)
		while (--idx >= 0) {
			i2c_unregister_device(ee1004_set_page[idx]);
			ee1004_set_page[idx] = NULL;
		}
}

static int ee1004_probe(struct i2c_client *client)
{
	int err, cnr = 0;

	/* Make sure we can operate on this adapter */
	if (!i2c_check_functionality(client->adapter,
				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
	    !i2c_check_functionality(client->adapter,
				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
		return -EPFNOSUPPORT;

	/* Use 2 dummy devices for page select command */
	mutex_lock(&ee1004_bus_lock);
	if (++ee1004_dev_count == 1) {
		for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
			struct i2c_client *cl;

			cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
			if (IS_ERR(cl)) {
				err = PTR_ERR(cl);
				goto err_clients;
			}
			ee1004_set_page[cnr] = cl;
		}

		/* Remember current page to avoid unneeded page select */
		err = ee1004_get_current_page();
		if (err < 0)
			goto err_clients;
		dev_dbg(&client->dev, "Currently selected page: %d\n", err);
		ee1004_current_page = err;
	} else if (client->adapter != ee1004_set_page[0]->adapter) {
		dev_err(&client->dev,
			"Driver only supports devices on a single I2C bus\n");
		err = -EOPNOTSUPP;
		goto err_clients;
	}
	mutex_unlock(&ee1004_bus_lock);

	dev_info(&client->dev,
		 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
		 EE1004_EEPROM_SIZE);

	return 0;

 err_clients:
	ee1004_cleanup(cnr);
	mutex_unlock(&ee1004_bus_lock);

	return err;
}

static int ee1004_remove(struct i2c_client *client)
{
	/* Remove page select clients if this is the last device */
	mutex_lock(&ee1004_bus_lock);
	ee1004_cleanup(EE1004_NUM_PAGES);
	mutex_unlock(&ee1004_bus_lock);

	return 0;
}

/*-------------------------------------------------------------------------*/

static struct i2c_driver ee1004_driver = {
	.driver = {
		.name = "ee1004",
		.dev_groups = ee1004_groups,
	},
	.probe_new = ee1004_probe,
	.remove = ee1004_remove,
	.id_table = ee1004_ids,
};
module_i2c_driver(ee1004_driver);

MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
MODULE_AUTHOR("Jean Delvare");
MODULE_LICENSE("GPL");