1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * ee1004 - driver for DDR4 SPD EEPROMs
4 *
5 * Copyright (C) 2017-2019 Jean Delvare
6 *
7 * Based on the at24 driver:
8 * Copyright (C) 2005-2007 David Brownell
9 * Copyright (C) 2008 Wolfram Sang, Pengutronix
10 */
11
12#include <linux/i2c.h>
13#include <linux/init.h>
14#include <linux/kernel.h>
15#include <linux/mod_devicetable.h>
16#include <linux/module.h>
17#include <linux/mutex.h>
18
19/*
20 * DDR4 memory modules use special EEPROMs following the Jedec EE1004
21 * specification. These are 512-byte EEPROMs using a single I2C address
22 * in the 0x50-0x57 range for data. One of two 256-byte page is selected
23 * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
24 *
25 * Therefore we need to request these 2 additional addresses, and serialize
26 * access to all such EEPROMs with a single mutex.
27 *
28 * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
29 * We use SMBus access even if I2C is available, these EEPROMs are small
30 * enough, and reading from them infrequent enough, that we favor simplicity
31 * over performance.
32 */
33
34#define EE1004_MAX_BUSSES		8
35#define EE1004_ADDR_SET_PAGE		0x36
36#define EE1004_NUM_PAGES		2
37#define EE1004_PAGE_SIZE		256
38#define EE1004_PAGE_SHIFT		8
39#define EE1004_EEPROM_SIZE		(EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
40
41/*
42 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
43 * from page selection to end of read.
44 */
45static DEFINE_MUTEX(ee1004_bus_lock);
46
47static struct ee1004_bus_data {
48	struct i2c_adapter *adap;
49	struct i2c_client *set_page[EE1004_NUM_PAGES];
50	unsigned int dev_count;
51	int current_page;
52} ee1004_bus_data[EE1004_MAX_BUSSES];
53
54static const struct i2c_device_id ee1004_ids[] = {
55	{ "ee1004", 0 },
56	{ }
57};
58MODULE_DEVICE_TABLE(i2c, ee1004_ids);
59
60/*-------------------------------------------------------------------------*/
61
62static struct ee1004_bus_data *ee1004_get_bus_data(struct i2c_adapter *adap)
63{
64	int i;
65
66	for (i = 0; i < EE1004_MAX_BUSSES; i++)
67		if (ee1004_bus_data[i].adap == adap)
68			return ee1004_bus_data + i;
69
70	/* If not existent yet, create new entry */
71	for (i = 0; i < EE1004_MAX_BUSSES; i++)
72		if (!ee1004_bus_data[i].adap) {
73			ee1004_bus_data[i].adap = adap;
74			return ee1004_bus_data + i;
75		}
76
77	return NULL;
78}
79
80static int ee1004_get_current_page(struct ee1004_bus_data *bd)
81{
82	int err;
83
84	err = i2c_smbus_read_byte(bd->set_page[0]);
85	if (err == -ENXIO) {
86		/* Nack means page 1 is selected */
87		return 1;
88	}
89	if (err < 0) {
90		/* Anything else is a real error, bail out */
91		return err;
92	}
93
94	/* Ack means page 0 is selected, returned value meaningless */
95	return 0;
96}
97
98static int ee1004_set_current_page(struct i2c_client *client, int page)
99{
100	struct ee1004_bus_data *bd = i2c_get_clientdata(client);
101	int ret;
102
103	if (page == bd->current_page)
104		return 0;
105
106	/* Data is ignored */
107	ret = i2c_smbus_write_byte(bd->set_page[page], 0x00);
108	/*
109	 * Don't give up just yet. Some memory modules will select the page
110	 * but not ack the command. Check which page is selected now.
111	 */
112	if (ret == -ENXIO && ee1004_get_current_page(bd) == page)
113		ret = 0;
114	if (ret < 0) {
115		dev_err(&client->dev, "Failed to select page %d (%d)\n", page, ret);
116		return ret;
117	}
118
119	dev_dbg(&client->dev, "Selected page %d\n", page);
120	bd->current_page = page;
121
122	return 0;
123}
124
125static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
126				  unsigned int offset, size_t count)
127{
128	int status, page;
129
130	page = offset >> EE1004_PAGE_SHIFT;
131	offset &= (1 << EE1004_PAGE_SHIFT) - 1;
132
133	status = ee1004_set_current_page(client, page);
134	if (status)
135		return status;
136
137	/* Can't cross page boundaries */
138	if (offset + count > EE1004_PAGE_SIZE)
139		count = EE1004_PAGE_SIZE - offset;
140
141	if (count > I2C_SMBUS_BLOCK_MAX)
142		count = I2C_SMBUS_BLOCK_MAX;
143
144	return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
145}
146
147static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
148			   struct bin_attribute *bin_attr,
149			   char *buf, loff_t off, size_t count)
150{
151	struct i2c_client *client = kobj_to_i2c_client(kobj);
152	size_t requested = count;
153	int ret = 0;
154
155	/*
156	 * Read data from chip, protecting against concurrent access to
157	 * other EE1004 SPD EEPROMs on the same adapter.
158	 */
159	mutex_lock(&ee1004_bus_lock);
160
161	while (count) {
162		ret = ee1004_eeprom_read(client, buf, off, count);
163		if (ret < 0)
164			goto out;
165
166		buf += ret;
167		off += ret;
168		count -= ret;
169	}
170out:
171	mutex_unlock(&ee1004_bus_lock);
172
173	return ret < 0 ? ret : requested;
174}
175
176static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);
177
178static struct bin_attribute *ee1004_attrs[] = {
179	&bin_attr_eeprom,
180	NULL
181};
182
183BIN_ATTRIBUTE_GROUPS(ee1004);
184
185static void ee1004_probe_temp_sensor(struct i2c_client *client)
186{
187	struct i2c_board_info info = { .type = "jc42" };
188	u8 byte14;
189	int ret;
190
191	/* byte 14, bit 7 is set if temp sensor is present */
192	ret = ee1004_eeprom_read(client, &byte14, 14, 1);
193	if (ret != 1 || !(byte14 & BIT(7)))
194		return;
195
196	info.addr = 0x18 | (client->addr & 7);
197
198	i2c_new_client_device(client->adapter, &info);
199}
200
201static void ee1004_cleanup(int idx, struct ee1004_bus_data *bd)
202{
203	if (--bd->dev_count == 0) {
204		while (--idx >= 0)
205			i2c_unregister_device(bd->set_page[idx]);
206		memset(bd, 0, sizeof(struct ee1004_bus_data));
207	}
208}
209
210static int ee1004_probe(struct i2c_client *client)
211{
212	struct ee1004_bus_data *bd;
213	int err, cnr = 0;
214
215	/* Make sure we can operate on this adapter */
216	if (!i2c_check_functionality(client->adapter,
217				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
218	    !i2c_check_functionality(client->adapter,
219				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
220		return -EPFNOSUPPORT;
221
222	mutex_lock(&ee1004_bus_lock);
223
224	bd = ee1004_get_bus_data(client->adapter);
225	if (!bd) {
226		mutex_unlock(&ee1004_bus_lock);
227		return dev_err_probe(&client->dev, -ENOSPC,
228				     "Only %d busses supported", EE1004_MAX_BUSSES);
229	}
230
231	i2c_set_clientdata(client, bd);
232
233	if (++bd->dev_count == 1) {
234		/* Use 2 dummy devices for page select command */
235		for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
236			struct i2c_client *cl;
237
238			cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
239			if (IS_ERR(cl)) {
240				err = PTR_ERR(cl);
241				goto err_clients;
242			}
243			bd->set_page[cnr] = cl;
244		}
245
246		/* Remember current page to avoid unneeded page select */
247		err = ee1004_get_current_page(bd);
248		if (err < 0)
249			goto err_clients;
250		dev_dbg(&client->dev, "Currently selected page: %d\n", err);
251		bd->current_page = err;
252	}
253
254	ee1004_probe_temp_sensor(client);
255
256	mutex_unlock(&ee1004_bus_lock);
257
258	dev_info(&client->dev,
259		 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
260		 EE1004_EEPROM_SIZE);
261
262	return 0;
263
264 err_clients:
265	ee1004_cleanup(cnr, bd);
266	mutex_unlock(&ee1004_bus_lock);
267
268	return err;
269}
270
271static void ee1004_remove(struct i2c_client *client)
272{
273	struct ee1004_bus_data *bd = i2c_get_clientdata(client);
274
275	/* Remove page select clients if this is the last device */
276	mutex_lock(&ee1004_bus_lock);
277	ee1004_cleanup(EE1004_NUM_PAGES, bd);
278	mutex_unlock(&ee1004_bus_lock);
279}
280
281/*-------------------------------------------------------------------------*/
282
283static struct i2c_driver ee1004_driver = {
284	.driver = {
285		.name = "ee1004",
286		.dev_groups = ee1004_groups,
287	},
288	.probe = ee1004_probe,
289	.remove = ee1004_remove,
290	.id_table = ee1004_ids,
291};
292module_i2c_driver(ee1004_driver);
293
294MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
295MODULE_AUTHOR("Jean Delvare");
296MODULE_LICENSE("GPL");
297