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About the PCF8575 chip: the PCF8575 is a 16-bit I/O expander for the I2C bus
produced by a.o. Philips Semiconductors.
Copyright (C) 2006 Michael Hennerich, Analog Devices Inc.
Based on pcf8574.c.
Copyright (c) 2007 Bart Van Assche <>.
Ported this driver from ucLinux to the mainstream Linux kernel.
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.
#include <linux/module.h>
#include <linux/init.h>
#include <linux/i2c.h>
#include <linux/slab.h> /* kzalloc() */
#include <linux/sysfs.h> /* sysfs_create_group() */
/* Addresses to scan */
static const unsigned short normal_i2c[] = {
0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
/* Insmod parameters */
/* Each client has this additional data */
struct pcf8575_data {
struct i2c_client client;
int write; /* last written value, or error code */
static int pcf8575_attach_adapter(struct i2c_adapter *adapter);
static int pcf8575_detect(struct i2c_adapter *adapter, int address, int kind);
static int pcf8575_detach_client(struct i2c_client *client);
/* This is the driver that will be inserted */
static struct i2c_driver pcf8575_driver = {
.driver = {
.owner = THIS_MODULE,
.name = "pcf8575",
.attach_adapter = pcf8575_attach_adapter,
.detach_client = pcf8575_detach_client,
/* following are the sysfs callback functions */
static ssize_t show_read(struct device *dev, struct device_attribute *attr,
char *buf)
struct i2c_client *client = to_i2c_client(dev);
u16 val;
u8 iopin_state[2];
i2c_master_recv(client, iopin_state, 2);
val = iopin_state[0];
val |= iopin_state[1] << 8;
return sprintf(buf, "%u\n", val);
static DEVICE_ATTR(read, S_IRUGO, show_read, NULL);
static ssize_t show_write(struct device *dev, struct device_attribute *attr,
char *buf)
struct pcf8575_data *data = dev_get_drvdata(dev);
if (data->write < 0)
return data->write;
return sprintf(buf, "%d\n", data->write);
static ssize_t set_write(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
struct i2c_client *client = to_i2c_client(dev);
struct pcf8575_data *data = i2c_get_clientdata(client);
unsigned long val = simple_strtoul(buf, NULL, 10);
u8 iopin_state[2];
if (val > 0xffff)
return -EINVAL;
data->write = val;
iopin_state[0] = val & 0xFF;
iopin_state[1] = val >> 8;
i2c_master_send(client, iopin_state, 2);
return count;
static DEVICE_ATTR(write, S_IWUSR | S_IRUGO, show_write, set_write);
static struct attribute *pcf8575_attributes[] = {
static const struct attribute_group pcf8575_attr_group = {
.attrs = pcf8575_attributes,
* Real code
static int pcf8575_attach_adapter(struct i2c_adapter *adapter)
return i2c_probe(adapter, &addr_data, pcf8575_detect);
/* This function is called by i2c_probe */
static int pcf8575_detect(struct i2c_adapter *adapter, int address, int kind)
struct i2c_client *client;
struct pcf8575_data *data;
int err = 0;
if (!i2c_check_functionality(adapter, I2C_FUNC_I2C))
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. */
data = kzalloc(sizeof(struct pcf8575_data), GFP_KERNEL);
if (!data) {
err = -ENOMEM;
goto exit;
client = &data->client;
i2c_set_clientdata(client, data);
client->addr = address;
client->adapter = adapter;
client->driver = &pcf8575_driver;
strlcpy(client->name, "pcf8575", I2C_NAME_SIZE);
data->write = -EAGAIN;
/* This is the place to detect whether the chip at the specified
address really is a PCF8575 chip. However, there is no method known
to detect whether an I2C chip is a PCF8575 or any other I2C chip. */
/* Tell the I2C layer a new client has arrived */
err = i2c_attach_client(client);
if (err)
goto exit_free;
/* Register sysfs hooks */
err = sysfs_create_group(&client->dev.kobj, &pcf8575_attr_group);
if (err)
goto exit_detach;
return 0;
return err;
static int pcf8575_detach_client(struct i2c_client *client)
int err;
sysfs_remove_group(&client->dev.kobj, &pcf8575_attr_group);
err = i2c_detach_client(client);
if (err)
return err;
return 0;
static int __init pcf8575_init(void)
return i2c_add_driver(&pcf8575_driver);
static void __exit pcf8575_exit(void)
MODULE_AUTHOR("Michael Hennerich <>, "
"Bart Van Assche <>");
MODULE_DESCRIPTION("pcf8575 driver");