linux/drivers/i2c/chips/max6875.c

268 lines
6.8 KiB
C
Raw Normal View History

/*
max6875.c - driver for MAX6874/MAX6875
Copyright (C) 2005 Ben Gardner <bgardner@wabtec.com>
Based on i2c/chips/eeprom.c
The MAX6875 has a bank of registers and two banks of EEPROM.
Address ranges are defined as follows:
* 0x0000 - 0x0046 = configuration registers
* 0x8000 - 0x8046 = configuration EEPROM
* 0x8100 - 0x82FF = user EEPROM
This driver makes the user EEPROM available for read.
The registers & config EEPROM should be accessed via i2c-dev.
The MAX6875 ignores the lowest address bit, so each chip responds to
two addresses - 0x50/0x51 and 0x52/0x53.
Note that the MAX6875 uses i2c_smbus_write_byte_data() to set the read
address, so this driver is destructive if loaded for the wrong EEPROM chip.
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; version 2 of the License.
*/
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/i2c-sensor.h>
#include <asm/semaphore.h>
/* Do not scan - the MAX6875 access method will write to some EEPROM chips */
[PATCH] I2C: New max6875 driver may corrupt EEPROMs After a careful code analysis on the new max6875 driver (drivers/i2c/chips/max6875.c), I have come to the conclusion that this driver may cause EEPROM corruptions if used on random systems. The EEPROM part of the MAX6875 chip is accessed using rather uncommon I2C sequences. What is seen by the MAX6875 as reads can be seen by a standard EEPROM (24C02) as writes. If you check the detection method used by the driver, you'll find that the first SMBus command it will send on the bus is i2c_smbus_write_byte_data(client, 0x80, 0x40). For the MAX6875 it makes an internal pointer point to a specific offset of the EEPROM waiting for a subsequent read command, so it's not an actual data write operation, but for a standard EEPROM, this instead means writing value 0x40 to offset 0x80. Blame Philips and Intel for the obscure protocol. Since the MAX6875 and the standard, common 24C02 EEPROMs share two I2C addresses (0x50 and 0x52), loading the max6875 driver on a system with standard EEPROMs at either address will trigger a write on these EEPROMs, which will lead to their corruption if they happen not to be write protected. This kind of EEPROMs can be found on memory modules (SPD), ethernet adapters (MAC address), laptops (proprietary data) and displays (EDID/DDC). Most of these are hopefully write-protected, but not all of them. For this reason, I would recommend that the max6875 driver be neutralized, in a way that nobody can corrupt his/her EEPROMs by just loading the driver. This means either deleting the driver completely, or not listing any default address for it. I'd like this to be done before 2.6.13-rc1 is released. Additionally, the max6875 driver lacks the 24RF08 corruption preventer present in the eeprom driver, which means that loading this driver in a system with such a chip would corrupt it as well. Here is a proposed quick patch addressing the issue, although I wouldn't mind a complete removal if it makes everyone feel safer. I think Ben has plans to replace this driver by a much simplified one anyway. Signed-off-by: Jean Delvare <khali@linux-fr.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2005-06-25 03:14:16 +08:00
static unsigned short normal_i2c[] = {I2C_CLIENT_END};
/* Insmod parameters */
SENSORS_INSMOD_1(max6875);
/* The MAX6875 can only read/write 16 bytes at a time */
#define SLICE_SIZE 16
#define SLICE_BITS 4
/* USER EEPROM is at addresses 0x8100 - 0x82FF */
#define USER_EEPROM_BASE 0x8100
#define USER_EEPROM_SIZE 0x0200
#define USER_EEPROM_SLICES 32
/* MAX6875 commands */
#define MAX6875_CMD_BLK_READ 0x84
/* Each client has this additional data */
struct max6875_data {
struct i2c_client client;
struct semaphore update_lock;
u32 valid;
u8 data[USER_EEPROM_SIZE];
unsigned long last_updated[USER_EEPROM_SLICES];
};
static int max6875_attach_adapter(struct i2c_adapter *adapter);
static int max6875_detect(struct i2c_adapter *adapter, int address, int kind);
static int max6875_detach_client(struct i2c_client *client);
/* This is the driver that will be inserted */
static struct i2c_driver max6875_driver = {
.owner = THIS_MODULE,
.name = "max6875",
.flags = I2C_DF_NOTIFY,
.attach_adapter = max6875_attach_adapter,
.detach_client = max6875_detach_client,
};
static void max6875_update_slice(struct i2c_client *client, int slice)
{
struct max6875_data *data = i2c_get_clientdata(client);
int i, j, addr;
u8 *buf;
if (slice >= USER_EEPROM_SLICES)
return;
down(&data->update_lock);
buf = &data->data[slice << SLICE_BITS];
if (!(data->valid & (1 << slice)) ||
time_after(jiffies, data->last_updated[slice])) {
dev_dbg(&client->dev, "Starting update of slice %u\n", slice);
data->valid &= ~(1 << slice);
addr = USER_EEPROM_BASE + (slice << SLICE_BITS);
/* select the eeprom address */
if (i2c_smbus_write_byte_data(client, addr >> 8, addr & 0xFF)) {
dev_err(&client->dev, "address set failed\n");
goto exit_up;
}
if (i2c_check_functionality(client->adapter,
I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
if (i2c_smbus_read_i2c_block_data(client,
MAX6875_CMD_BLK_READ,
buf) != SLICE_SIZE) {
goto exit_up;
}
} else {
for (i = 0; i < SLICE_SIZE; i++) {
j = i2c_smbus_read_byte(client);
if (j < 0) {
goto exit_up;
}
buf[i] = j;
}
}
data->last_updated[slice] = jiffies;
data->valid |= (1 << slice);
}
exit_up:
up(&data->update_lock);
}
static ssize_t max6875_read(struct kobject *kobj, char *buf, loff_t off,
size_t count)
{
struct i2c_client *client = kobj_to_i2c_client(kobj);
struct max6875_data *data = i2c_get_clientdata(client);
int slice, max_slice;
if (off > USER_EEPROM_SIZE)
return 0;
if (off + count > USER_EEPROM_SIZE)
count = USER_EEPROM_SIZE - off;
/* refresh slices which contain requested bytes */
max_slice = (off + count - 1) >> SLICE_BITS;
for (slice = (off >> SLICE_BITS); slice <= max_slice; slice++)
max6875_update_slice(client, slice);
memcpy(buf, &data->data[off], count);
return count;
}
static struct bin_attribute user_eeprom_attr = {
.attr = {
.name = "eeprom",
.mode = S_IRUGO,
.owner = THIS_MODULE,
},
.size = USER_EEPROM_SIZE,
.read = max6875_read,
};
static int max6875_attach_adapter(struct i2c_adapter *adapter)
{
return i2c_detect(adapter, &addr_data, max6875_detect);
}
/* This function is called by i2c_detect */
static int max6875_detect(struct i2c_adapter *adapter, int address, int kind)
{
struct i2c_client *real_client;
struct i2c_client *fake_client;
struct max6875_data *data;
int err = 0;
/* Prevent 24rf08 corruption (in case of user error) */
if (kind < 0)
i2c_smbus_xfer(adapter, address, 0, 0, 0,
I2C_SMBUS_QUICK, NULL);
if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WRITE_BYTE_DATA
| I2C_FUNC_SMBUS_READ_BYTE))
return 0;
/* Only check even addresses */
if (address & 1)
return 0;
if (!(data = kmalloc(sizeof(struct max6875_data), GFP_KERNEL)))
return -ENOMEM;
memset(data, 0, sizeof(struct max6875_data));
/* A fake client is created on the odd address */
if (!(fake_client = kmalloc(sizeof(struct i2c_client), GFP_KERNEL))) {
err = -ENOMEM;
goto exit_kfree1;
}
memset(fake_client, 0, sizeof(struct i2c_client));
/* Init real i2c_client */
real_client = &data->client;
i2c_set_clientdata(real_client, data);
real_client->addr = address;
real_client->adapter = adapter;
real_client->driver = &max6875_driver;
real_client->flags = 0;
strlcpy(real_client->name, "max6875", I2C_NAME_SIZE);
init_MUTEX(&data->update_lock);
/* Init fake client data */
/* set the client data to the i2c_client so that it will get freed */
i2c_set_clientdata(fake_client, fake_client);
fake_client->addr = address | 1;
fake_client->adapter = adapter;
fake_client->driver = &max6875_driver;
fake_client->flags = 0;
strlcpy(fake_client->name, "max6875 subclient", I2C_NAME_SIZE);
/* Prevent 24RF08 corruption (in case of user error) */
i2c_smbus_write_quick(real_client, 0);
if ((err = i2c_attach_client(real_client)) != 0)
goto exit_kfree2;
if ((err = i2c_attach_client(fake_client)) != 0)
goto exit_detach;
sysfs_create_bin_file(&real_client->dev.kobj, &user_eeprom_attr);
return 0;
exit_detach:
i2c_detach_client(real_client);
exit_kfree2:
kfree(fake_client);
exit_kfree1:
kfree(data);
return err;
}
static int max6875_detach_client(struct i2c_client *client)
{
int err;
err = i2c_detach_client(client);
if (err)
return err;
kfree(i2c_get_clientdata(client));
return 0;
}
static int __init max6875_init(void)
{
return i2c_add_driver(&max6875_driver);
}
static void __exit max6875_exit(void)
{
i2c_del_driver(&max6875_driver);
}
MODULE_AUTHOR("Ben Gardner <bgardner@wabtec.com>");
MODULE_DESCRIPTION("MAX6875 driver");
MODULE_LICENSE("GPL");
module_init(max6875_init);
module_exit(max6875_exit);