// 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 #include #include #include #include #include /* * 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_EEPROM_SIZE 512 #define EE1004_PAGE_SIZE 256 #define EE1004_PAGE_SHIFT 8 /* * 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[2]; 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 ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf, unsigned int offset, size_t count) { int status; /* Can't cross page boundaries */ if (offset + count > EE1004_PAGE_SIZE) count = EE1004_PAGE_SIZE - offset; status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf); dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status); return status; } 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 page; page = off >> EE1004_PAGE_SHIFT; if (unlikely(page > 1)) return 0; off &= (1 << EE1004_PAGE_SHIFT) - 1; /* * Read data from chip, protecting against concurrent access to * other EE1004 SPD EEPROMs on the same adapter. */ mutex_lock(&ee1004_bus_lock); while (count) { int status; /* Select page */ if (page != ee1004_current_page) { /* Data is ignored */ status = i2c_smbus_write_byte(ee1004_set_page[page], 0x00); if (status == -ENXIO) { /* * 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 (ee1004_get_current_page() == page) status = 0; } if (status < 0) { dev_err(dev, "Failed to select page %d (%d)\n", page, status); mutex_unlock(&ee1004_bus_lock); return status; } dev_dbg(dev, "Selected page %d\n", page); ee1004_current_page = page; } status = ee1004_eeprom_read(client, buf, off, count); if (status < 0) { mutex_unlock(&ee1004_bus_lock); return status; } buf += status; off += status; count -= status; if (off == EE1004_PAGE_SIZE) { page++; off = 0; } } mutex_unlock(&ee1004_bus_lock); return requested; } static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE); static struct bin_attribute *ee1004_attrs[] = { &bin_attr_eeprom, NULL }; BIN_ATTRIBUTE_GROUPS(ee1004); 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 < 2; 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; } } 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; } /* Remember current page to avoid unneeded page select */ err = ee1004_get_current_page(); if (err < 0) goto err_clients; ee1004_current_page = err; dev_dbg(&client->dev, "Currently selected page: %d\n", ee1004_current_page); 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: if (--ee1004_dev_count == 0) { for (cnr--; cnr >= 0; cnr--) { i2c_unregister_device(ee1004_set_page[cnr]); ee1004_set_page[cnr] = NULL; } } mutex_unlock(&ee1004_bus_lock); return err; } static int ee1004_remove(struct i2c_client *client) { int i; /* Remove page select clients if this is the last device */ mutex_lock(&ee1004_bus_lock); if (--ee1004_dev_count == 0) { for (i = 0; i < 2; i++) { i2c_unregister_device(ee1004_set_page[i]); ee1004_set_page[i] = NULL; } } 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");