i2c: Add support for the PCF8575 chip

About the PCF8575 chip and the pcf8575 kernel driver

====================================================

The PCF8575 chip is produced by the following manufacturers:

  * Philips NXP

    http://www.nxp.com/#/pip/cb=[type=product,path=50807/41735/41850,final=PCF8575_3]|pip=[pip=PCF8575_3][0]

  * Texas Instruments

    http://focus.ti.com/docs/prod/folders/print/pcf8575.html

Some vendors sell small PCB's with the PCF8575 mounted on it. You can connect

such a board to a Linux host via e.g. an USB to I2C interface. Examples of

PCB boards with a PCF8575:

  * SFE Breakout Board for PCF8575 I2C Expander by RobotShop

    http://www.robotshop.ca/home/products/robot-parts/electronics/adapters-converters/sfe-pcf8575-i2c-expander-board.html

  * Breakout Board for PCF8575 I2C Expander by Spark Fun Electronics

    http://www.sparkfun.com/commerce/product_info.php?products_id=8130

Description

-----------

The PCF8575 chip is a 16-bit I/O expander for the I2C bus. Up to eight of

these chips can be connected to the same I2C bus. You can find this

chip on some custom designed hardware, but you won't find it on PC

motherboards.

The PCF8575 chip consists of a 16-bit quasi-bidirectional port and an I2C-bus

interface. Each of the sixteen I/O's can be independently used as an input or

an output. To set up an I/O pin as an input, you have to write a 1 to the

corresponding output.

For more information please see the datasheet.

Detection

---------

There is no method known to detect whether a chip on a given I2C address is

a PCF8575 or whether it is any other I2C device. So there are two alternatives

to let the driver find the installed PCF8575 devices:

- Load this driver after any other I2C driver for I2C devices with addresses

  in the range 0x20 .. 0x27.

- Pass the I2C bus and address of the installed PCF8575 devices explicitly to

  the driver at load time via the probe=... or force=... parameters.

/sys interface

--------------

For each address on which a PCF8575 chip was found or forced the following

files will be created under /sys:

* /sys/bus/i2c/devices/<bus>-<address>/read

* /sys/bus/i2c/devices/<bus>-<address>/write

where bus is the I2C bus number (0, 1, ...) and address is the four-digit

hexadecimal representation of the 7-bit I2C address of the PCF8575

(0020 .. 0027).

The read file is read-only. Reading it will trigger an I2C read and will hence

report the current input state for the pins configured as inputs, and the

current output value for the pins configured as outputs.

The write file is read-write. Writing a value to it will configure all pins

as output for which the corresponding bit is zero. Reading the write file will

return the value last written, or -EAGAIN if no value has yet been written to

the write file.

On module initialization the configuration of the chip is not changed -- the

chip is left in the state it was already configured in through either power-up

or through previous I2C write actions.

	default n

	help

	  If you say yes here you get support for Philips PCF8574 and 

	  PCF8574A chips.

	  PCF8574A chips. These chips are 8-bit I/O expanders for the I2C bus.

	  This driver can also be built as a module.  If so, the module

	  will be called pcf8574.

	  These devices are hard to detect and rarely found on mainstream

	  hardware.  If unsure, say N.

config PCF8575

	tristate "Philips PCF8575"

	default n

	help

	  If you say yes here you get support for Philips PCF8575 chip.

	  This chip is a 16-bit I/O expander for the I2C bus.  Several other

	  chip manufacturers sell equivalent chips, e.g. Texas Instruments.

	  This driver can also be built as a module.  If so, the module

	  will be called pcf8575.

	  This device is hard to detect and is rarely found on mainstream

	  hardware.  If unsure, say N.

config SENSORS_PCA9539

	tristate "Philips PCA9539 16-bit I/O port"

	depends on EXPERIMENTAL

obj-$(CONFIG_SENSORS_M41T00)	+= m41t00.o

obj-$(CONFIG_SENSORS_PCA9539)	+= pca9539.o

obj-$(CONFIG_SENSORS_PCF8574)	+= pcf8574.o

obj-$(CONFIG_PCF8575)		+= pcf8575.o

obj-$(CONFIG_SENSORS_PCF8591)	+= pcf8591.o

obj-$(CONFIG_ISP1301_OMAP)	+= isp1301_omap.o

obj-$(CONFIG_TPS65010)		+= tps65010.o

/*

  pcf8575.c

  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.

  <hennerich@blackfin.uclinux.org>

  Based on pcf8574.c.

  Copyright (c) 2007 Bart Van Assche <bart.vanassche@gmail.com>.

  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

  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  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 unsigned short normal_i2c[] = {

	0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,

	I2C_CLIENT_END

};

/* Insmod parameters */

I2C_CLIENT_INSMOD;

/* 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[] = {

	&dev_attr_read.attr,

	&dev_attr_write.attr,

	NULL

};

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;

exit_detach:

	i2c_detach_client(client);

exit_free:

	kfree(data);

exit:

	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;

	kfree(i2c_get_clientdata(client));

	return 0;

}

static int __init pcf8575_init(void)

{

	return i2c_add_driver(&pcf8575_driver);

}

static void __exit pcf8575_exit(void)

{

	i2c_del_driver(&pcf8575_driver);

}

MODULE_AUTHOR("Michael Hennerich <hennerich@blackfin.uclinux.org>, "

	      "Bart Van Assche <bart.vanassche@gmail.com>");

MODULE_DESCRIPTION("pcf8575 driver");

MODULE_LICENSE("GPL");

module_init(pcf8575_init);

module_exit(pcf8575_exit);