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pcf8574.c - Part of lm_sensors, Linux kernel modules for hardware
Copyright (c) 2000 Frodo Looijaard <>,
Philip Edelbrock <>,
Dan Eaton <>
Ported to Linux 2.6 by Aurelien Jarno <> with
the help of Jean Delvare <>
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.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
/* A few notes about the PCF8574:
* The PCF8574 is an 8-bit I/O expander for the I2C bus produced by
Philips Semiconductors. It is designed to provide a byte I2C
interface to up to 8 separate devices.
* The PCF8574 appears as a very simple SMBus device which can be
read from or written to with SMBUS byte read/write accesses.
#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/i2c-sensor.h>
/* Addresses to scan */
static unsigned short normal_i2c[] = { 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
static unsigned int normal_isa[] = { I2C_CLIENT_ISA_END };
/* Insmod parameters */
SENSORS_INSMOD_2(pcf8574, pcf8574a);
/* Initial values */
#define PCF8574_INIT 255 /* All outputs on (input mode) */
/* Each client has this additional data */
struct pcf8574_data {
struct i2c_client client;
u8 read, write; /* Register values */
static int pcf8574_attach_adapter(struct i2c_adapter *adapter);
static int pcf8574_detect(struct i2c_adapter *adapter, int address, int kind);
static int pcf8574_detach_client(struct i2c_client *client);
static void pcf8574_init_client(struct i2c_client *client);
/* This is the driver that will be inserted */
static struct i2c_driver pcf8574_driver = {
.owner = THIS_MODULE,
.name = "pcf8574",
.id = I2C_DRIVERID_PCF8574,
.flags = I2C_DF_NOTIFY,
.attach_adapter = pcf8574_attach_adapter,
.detach_client = pcf8574_detach_client,
/* following are the sysfs callback functions */
static ssize_t show_read(struct device *dev, char *buf)
struct i2c_client *client = to_i2c_client(dev);
struct pcf8574_data *data = i2c_get_clientdata(client);
data->read = i2c_smbus_read_byte(client);
return sprintf(buf, "%u\n", data->read);
static DEVICE_ATTR(read, S_IRUGO, show_read, NULL);
static ssize_t show_write(struct device *dev, char *buf)
struct pcf8574_data *data = i2c_get_clientdata(to_i2c_client(dev));
return sprintf(buf, "%u\n", data->write);
static ssize_t set_write(struct device *dev, const char *buf,
size_t count)
struct i2c_client *client = to_i2c_client(dev);
struct pcf8574_data *data = i2c_get_clientdata(client);
unsigned long val = simple_strtoul(buf, NULL, 10);
if (val > 0xff)
return -EINVAL;
data->write = val;
i2c_smbus_write_byte(client, data->write);
return count;
static DEVICE_ATTR(write, S_IWUSR | S_IRUGO, show_write, set_write);
* Real code
static int pcf8574_attach_adapter(struct i2c_adapter *adapter)
return i2c_detect(adapter, &addr_data, pcf8574_detect);
/* This function is called by i2c_detect */
int pcf8574_detect(struct i2c_adapter *adapter, int address, int kind)
struct i2c_client *new_client;
struct pcf8574_data *data;
int err = 0;
const char *client_name = "";
if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE))
goto exit;
/* OK. For now, we presume we have a valid client. We now create the
client structure, even though we cannot fill it completely yet. */
if (!(data = kmalloc(sizeof(struct pcf8574_data), GFP_KERNEL))) {
err = -ENOMEM;
goto exit;
memset(data, 0, sizeof(struct pcf8574_data));
new_client = &data->client;
i2c_set_clientdata(new_client, data);
new_client->addr = address;
new_client->adapter = adapter;
new_client->driver = &pcf8574_driver;
new_client->flags = 0;
/* Now, we would do the remaining detection. But the PCF8574 is plainly
impossible to detect! Stupid chip. */
/* Determine the chip type */
if (kind <= 0) {
if (address >= 0x38 && address <= 0x3f)
kind = pcf8574a;
kind = pcf8574;
if (kind == pcf8574a)
client_name = "pcf8574a";
client_name = "pcf8574";
/* Fill in the remaining client fields and put it into the global list */
strlcpy(new_client->name, client_name, I2C_NAME_SIZE);
/* Tell the I2C layer a new client has arrived */
if ((err = i2c_attach_client(new_client)))
goto exit_free;
/* Initialize the PCF8574 chip */
/* Register sysfs hooks */
device_create_file(&new_client->dev, &dev_attr_read);
device_create_file(&new_client->dev, &dev_attr_write);
return 0;
/* OK, this is not exactly good programming practice, usually. But it is
very code-efficient in this case. */
return err;
static int pcf8574_detach_client(struct i2c_client *client)
int err;
if ((err = i2c_detach_client(client))) {
"Client deregistration failed, client not detached.\n");
return err;
return 0;
/* Called when we have found a new PCF8574. */
static void pcf8574_init_client(struct i2c_client *client)
struct pcf8574_data *data = i2c_get_clientdata(client);
data->write = PCF8574_INIT;
i2c_smbus_write_byte(client, data->write);
static int __init pcf8574_init(void)
return i2c_add_driver(&pcf8574_driver);
static void __exit pcf8574_exit(void)
("Frodo Looijaard <>, "
"Philip Edelbrock <>, "
"Dan Eaton <> "
"and Aurelien Jarno <>");