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Subject[PATCH] eeprom: New ee1004 driver for DDR4 memory
The EEPROMs which hold the SPD data on DDR4 memory modules are no
longer standard AT24C02-compatible EEPROMs. They are 512-byte EEPROMs
which use only 1 I2C address for data access. You need to switch
between the lower page and the upper page of data by sending commands
on the SMBus.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
---
drivers/misc/eeprom/Kconfig | 11 +
drivers/misc/eeprom/Makefile | 1
drivers/misc/eeprom/ee1004.c | 281 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 293 insertions(+)

--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-4.14/drivers/misc/eeprom/ee1004.c 2017-11-19 20:53:48.088700027 +0100
@@ -0,0 +1,281 @@
+/*
+ * ee1004 - driver for DDR4 SPD EEPROMs
+ *
+ * Copyright (C) 2017 Jean Delvare
+ *
+ * Based on the at24 driver:
+ * Copyright (C) 2005-2007 David Brownell
+ * Copyright (C) 2008 Wolfram Sang, Pengutronix
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#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_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 ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
+ unsigned int offset, size_t count)
+{
+ int status;
+
+ if (count > I2C_SMBUS_BLOCK_MAX)
+ count = I2C_SMBUS_BLOCK_MAX;
+ /* Can't cross page boundaries */
+ if (unlikely(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 ee1004_read(struct file *filp, struct kobject *kobj,
+ struct bin_attribute *bin_attr,
+ char *buf, loff_t off, size_t count)
+{
+ struct device *dev = kobj_to_dev(kobj);
+ struct i2c_client *client = to_i2c_client(dev);
+ size_t requested = count;
+ int page;
+
+ if (unlikely(!count))
+ return count;
+
+ 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 < 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 const struct bin_attribute eeprom_attr = {
+ .attr = {
+ .name = "eeprom",
+ .mode = 0444,
+ },
+ .size = EE1004_EEPROM_SIZE,
+ .read = ee1004_read,
+};
+
+static int ee1004_probe(struct i2c_client *client,
+ const struct i2c_device_id *id)
+{
+ int err, cnr = 0;
+ const char *slow = NULL;
+
+ /* Make sure we can operate on this adapter */
+ if (!i2c_check_functionality(client->adapter,
+ I2C_FUNC_SMBUS_READ_BYTE |
+ I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
+ if (i2c_check_functionality(client->adapter,
+ I2C_FUNC_SMBUS_READ_BYTE |
+ I2C_FUNC_SMBUS_READ_WORD_DATA))
+ slow = "word";
+ else if (i2c_check_functionality(client->adapter,
+ I2C_FUNC_SMBUS_READ_BYTE |
+ I2C_FUNC_SMBUS_READ_BYTE_DATA))
+ slow = "byte";
+ else
+ 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++) {
+ ee1004_set_page[cnr] = i2c_new_dummy(client->adapter,
+ EE1004_ADDR_SET_PAGE + cnr);
+ if (!ee1004_set_page[cnr]) {
+ dev_err(&client->dev,
+ "address 0x%02x unavailable\n",
+ EE1004_ADDR_SET_PAGE + cnr);
+ err = -EADDRINUSE;
+ goto err_clients;
+ }
+ }
+ } else if (i2c_adapter_id(client->adapter) !=
+ i2c_adapter_id(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 = i2c_smbus_read_byte(ee1004_set_page[0]);
+ if (err == -ENXIO) {
+ /* Nack means page 1 is selected */
+ ee1004_current_page = 1;
+ } else if (err < 0) {
+ /* Anything else is a real error, bail out */
+ goto err_clients;
+ } else {
+ /* Ack means page 0 is selected, returned value meaningless */
+ ee1004_current_page = 0;
+ }
+ dev_dbg(&client->dev, "Currently selected page: %d\n",
+ ee1004_current_page);
+ mutex_unlock(&ee1004_bus_lock);
+
+ /* Create the sysfs eeprom file */
+ err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
+ if (err)
+ goto err_clients_lock;
+
+ dev_info(&client->dev,
+ "%u byte EE1004-compliant SPD EEPROM, read-only\n",
+ EE1004_EEPROM_SIZE);
+ if (slow)
+ dev_notice(&client->dev,
+ "Falling back to %s reads, performance will suffer\n",
+ slow);
+
+ return 0;
+
+ err_clients_lock:
+ mutex_lock(&ee1004_bus_lock);
+ 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;
+
+ sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
+
+ /* 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",
+ },
+ .probe = ee1004_probe,
+ .remove = ee1004_remove,
+ .id_table = ee1004_ids,
+};
+
+static int __init ee1004_init(void)
+{
+ return i2c_add_driver(&ee1004_driver);
+}
+module_init(ee1004_init);
+
+static void __exit ee1004_exit(void)
+{
+ i2c_del_driver(&ee1004_driver);
+}
+module_exit(ee1004_exit);
+
+MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
+MODULE_AUTHOR("Jean Delvare");
+MODULE_LICENSE("GPL");
--- linux-4.14.orig/drivers/misc/eeprom/Kconfig 2017-11-12 19:46:13.000000000 +0100
+++ linux-4.14/drivers/misc/eeprom/Kconfig 2017-11-19 17:40:16.108218699 +0100
@@ -110,4 +110,15 @@ config EEPROM_IDT_89HPESX
This driver can also be built as a module. If so, the module
will be called idt_89hpesx.

+config EEPROM_EE1004
+ tristate "SPD EEPROMs on DDR4 memory modules"
+ depends on I2C && SYSFS
+ help
+ Enable this driver to get read support to SPD EEPROMs following
+ the JEDEC EE1004 standard. These are typically found on DDR4
+ SDRAM memory modules.
+
+ This driver can also be built as a module. If so, the module
+ will be called ee1004.
+
endmenu
--- linux-4.14.orig/drivers/misc/eeprom/Makefile 2017-11-12 19:46:13.000000000 +0100
+++ linux-4.14/drivers/misc/eeprom/Makefile 2017-11-19 17:41:51.436359955 +0100
@@ -7,3 +7,4 @@ obj-$(CONFIG_EEPROM_93CX6) += eeprom_93c
obj-$(CONFIG_EEPROM_93XX46) += eeprom_93xx46.o
obj-$(CONFIG_EEPROM_DIGSY_MTC_CFG) += digsy_mtc_eeprom.o
obj-$(CONFIG_EEPROM_IDT_89HPESX) += idt_89hpesx.o
+obj-$(CONFIG_EEPROM_EE1004) += ee1004.o

--
Jean Delvare
SUSE L3 Support

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