drivers/i2c/i2c-core.c

/* i2c-core.c - a device driver for the iic-bus interface		     */
/* ------------------------------------------------------------------------- */
/*   Copyright (C) 1995-99 Simon G. Vogl

    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.		     */
/* ------------------------------------------------------------------------- */

/* With some changes from Kyösti Mälkki <kmalkki@cc.hut.fi>.
   All SMBus-related things are written by Frodo Looijaard <frodol@dds.nl>
   SMBus 2.0 support by Mark Studebaker <mdsxyz123@yahoo.com> and
   Jean Delvare <khali@linux-fr.org> */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/idr.h>
#include <linux/mutex.h>
#include <linux/completion.h>
#include <linux/hardirq.h>
#include <linux/irqflags.h>
#include <asm/uaccess.h>

#include "i2c-core.h"


static DEFINE_MUTEX(core_lock);
static DEFINE_IDR(i2c_adapter_idr);

#define is_newstyle_driver(d) ((d)->probe || (d)->remove || (d)->detect)

static int i2c_check_addr(struct i2c_adapter *adapter, int addr);
static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver);

/* ------------------------------------------------------------------------- */

static const struct i2c_device_id *i2c_match_id(const struct i2c_device_id *id,
						const struct i2c_client *client)
{
	while (id->name[0]) {
		if (strcmp(client->name, id->name) == 0)
			return id;
		id++;
	}
	return NULL;
}

static int i2c_device_match(struct device *dev, struct device_driver *drv)
{
	struct i2c_client	*client = to_i2c_client(dev);
	struct i2c_driver	*driver = to_i2c_driver(drv);

	/* make legacy i2c drivers bypass driver model probing entirely;
	 * such drivers scan each i2c adapter/bus themselves.
	 */
	if (!is_newstyle_driver(driver))
		return 0;

	/* match on an id table if there is one */
	if (driver->id_table)
		return i2c_match_id(driver->id_table, client) != NULL;

	return 0;
}

#ifdef	CONFIG_HOTPLUG

/* uevent helps with hotplug: modprobe -q $(MODALIAS) */
static int i2c_device_uevent(struct device *dev, struct kobj_uevent_env *env)
{
	struct i2c_client	*client = to_i2c_client(dev);

	if (add_uevent_var(env, "MODALIAS=%s%s",
			   I2C_MODULE_PREFIX, client->name))
		return -ENOMEM;
	dev_dbg(dev, "uevent\n");
	return 0;
}

#else
#define i2c_device_uevent	NULL
#endif	/* CONFIG_HOTPLUG */

static int i2c_device_probe(struct device *dev)
{
	struct i2c_client	*client = to_i2c_client(dev);
	struct i2c_driver	*driver = to_i2c_driver(dev->driver);
	int status;

	if (!driver->probe || !driver->id_table)
		return -ENODEV;
	client->driver = driver;
	if (!device_can_wakeup(&client->dev))
		device_init_wakeup(&client->dev,
					client->flags & I2C_CLIENT_WAKE);
	dev_dbg(dev, "probe\n");

	status = driver->probe(client, i2c_match_id(driver->id_table, client));
	if (status)
		client->driver = NULL;
	return status;
}

static int i2c_device_remove(struct device *dev)
{
	struct i2c_client	*client = to_i2c_client(dev);
	struct i2c_driver	*driver;
	int			status;

	if (!dev->driver)
		return 0;

	driver = to_i2c_driver(dev->driver);
	if (driver->remove) {
		dev_dbg(dev, "remove\n");
		status = driver->remove(client);
	} else {
		dev->driver = NULL;
		status = 0;
	}
	if (status == 0)
		client->driver = NULL;
	return status;
}

static void i2c_device_shutdown(struct device *dev)
{
	struct i2c_driver *driver;

	if (!dev->driver)
		return;
	driver = to_i2c_driver(dev->driver);
	if (driver->shutdown)
		driver->shutdown(to_i2c_client(dev));
}

static int i2c_device_suspend(struct device *dev, pm_message_t mesg)
{
	struct i2c_driver *driver;

	if (!dev->driver)
		return 0;
	driver = to_i2c_driver(dev->driver);
	if (!driver->suspend)
		return 0;
	return driver->suspend(to_i2c_client(dev), mesg);
}

static int i2c_device_resume(struct device *dev)
{
	struct i2c_driver *driver;

	if (!dev->driver)
		return 0;
	driver = to_i2c_driver(dev->driver);
	if (!driver->resume)
		return 0;
	return driver->resume(to_i2c_client(dev));
}

static void i2c_client_release(struct device *dev)
{
	struct i2c_client *client = to_i2c_client(dev);
	complete(&client->released);
}

static void i2c_client_dev_release(struct device *dev)
{
	kfree(to_i2c_client(dev));
}

static ssize_t
show_client_name(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct i2c_client *client = to_i2c_client(dev);
	return sprintf(buf, "%s\n", client->name);
}

static ssize_t
show_modalias(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct i2c_client *client = to_i2c_client(dev);
	return sprintf(buf, "%s%s\n", I2C_MODULE_PREFIX, client->name);
}

static struct device_attribute i2c_dev_attrs[] = {
	__ATTR(name, S_IRUGO, show_client_name, NULL),
	/* modalias helps coldplug:  modprobe $(cat .../modalias) */
	__ATTR(modalias, S_IRUGO, show_modalias, NULL),
	{ },
};

struct bus_type i2c_bus_type = {
	.name		= "i2c",
	.dev_attrs	= i2c_dev_attrs,
	.match		= i2c_device_match,
	.uevent		= i2c_device_uevent,
	.probe		= i2c_device_probe,
	.remove		= i2c_device_remove,
	.shutdown	= i2c_device_shutdown,
	.suspend	= i2c_device_suspend,
	.resume		= i2c_device_resume,
};
EXPORT_SYMBOL_GPL(i2c_bus_type);


/**
 * i2c_verify_client - return parameter as i2c_client, or NULL
 * @dev: device, probably from some driver model iterator
 *
 * When traversing the driver model tree, perhaps using driver model
 * iterators like @device_for_each_child(), you can't assume very much
 * about the nodes you find.  Use this function to avoid oopses caused
 * by wrongly treating some non-I2C device as an i2c_client.
 */
struct i2c_client *i2c_verify_client(struct device *dev)
{
	return (dev->bus == &i2c_bus_type)
			? to_i2c_client(dev)
			: NULL;
}
EXPORT_SYMBOL(i2c_verify_client);


/**
 * i2c_new_device - instantiate an i2c device
 * @adap: the adapter managing the device
 * @info: describes one I2C device; bus_num is ignored
 * Context: can sleep
 *
 * Create an i2c device. Binding is handled through driver model
 * probe()/remove() methods.  A driver may be bound to this device when we
 * return from this function, or any later moment (e.g. maybe hotplugging will
 * load the driver module).  This call is not appropriate for use by mainboard
 * initialization logic, which usually runs during an arch_initcall() long
 * before any i2c_adapter could exist.
 *
 * This returns the new i2c client, which may be saved for later use with
 * i2c_unregister_device(); or NULL to indicate an error.
 */
struct i2c_client *
i2c_new_device(struct i2c_adapter *adap, struct i2c_board_info const *info)
{
	struct i2c_client	*client;
	int			status;

	client = kzalloc(sizeof *client, GFP_KERNEL);
	if (!client)
		return NULL;

	client->adapter = adap;

	client->dev.platform_data = info->platform_data;

	if (info->archdata)
		client->dev.archdata = *info->archdata;

	client->flags = info->flags;
	client->addr = info->addr;
	client->irq = info->irq;

	strlcpy(client->name, info->type, sizeof(client->name));

	/* Check for address business */
	status = i2c_check_addr(adap, client->addr);
	if (status)
		goto out_err;

	client->dev.parent = &client->adapter->dev;
	client->dev.bus = &i2c_bus_type;

	if (client->driver && !is_newstyle_driver(client->driver)) {
		client->dev.release = i2c_client_release;
		dev_set_uevent_suppress(&client->dev, 1);
	} else
		client->dev.release = i2c_client_dev_release;

	dev_set_name(&client->dev, "%d-%04x", i2c_adapter_id(adap),
		     client->addr);
	status = device_register(&client->dev);
	if (status)
		goto out_err;

	mutex_lock(&adap->clist_lock);
	list_add_tail(&client->list, &adap->clients);
	mutex_unlock(&adap->clist_lock);

	dev_dbg(&adap->dev, "client [%s] registered with bus id %s\n",
		client->name, dev_name(&client->dev));

	return client;

out_err:
	dev_err(&adap->dev, "Failed to register i2c client %s at 0x%02x "
		"(%d)\n", client->name, client->addr, status);
	kfree(client);
	return NULL;
}
EXPORT_SYMBOL_GPL(i2c_new_device);


/**
 * i2c_unregister_device - reverse effect of i2c_new_device()
 * @client: value returned from i2c_new_device()
 * Context: can sleep
 */
void i2c_unregister_device(struct i2c_client *client)
{
	struct i2c_adapter	*adapter = client->adapter;
	struct i2c_driver	*driver = client->driver;

	if (driver && !is_newstyle_driver(driver)) {
		dev_err(&client->dev, "can't unregister devices "
			"with legacy drivers\n");
		WARN_ON(1);
		return;
	}

	mutex_lock(&adapter->clist_lock);
	list_del(&client->list);
	mutex_unlock(&adapter->clist_lock);

	device_unregister(&client->dev);
}
EXPORT_SYMBOL_GPL(i2c_unregister_device);


static const struct i2c_device_id dummy_id[] = {
	{ "dummy", 0 },
	{ },
};

static int dummy_probe(struct i2c_client *client,
		       const struct i2c_device_id *id)
{
	return 0;
}

static int dummy_remove(struct i2c_client *client)
{
	return 0;
}

static struct i2c_driver dummy_driver = {
	.driver.name	= "dummy",
	.probe		= dummy_probe,
	.remove		= dummy_remove,
	.id_table	= dummy_id,
};

/**
 * i2c_new_dummy - return a new i2c device bound to a dummy driver
 * @adapter: the adapter managing the device
 * @address: seven bit address to be used
 * Context: can sleep
 *
 * This returns an I2C client bound to the "dummy" driver, intended for use
 * with devices that consume multiple addresses.  Examples of such chips
 * include various EEPROMS (like 24c04 and 24c08 models).
 *
 * These dummy devices have two main uses.  First, most I2C and SMBus calls
 * except i2c_transfer() need a client handle; the dummy will be that handle.
 * And second, this prevents the specified address from being bound to a
 * different driver.
 *
 * This returns the new i2c client, which should be saved for later use with
 * i2c_unregister_device(); or NULL to indicate an error.
 */
struct i2c_client *i2c_new_dummy(struct i2c_adapter *adapter, u16 address)
{
	struct i2c_board_info info = {
		I2C_BOARD_INFO("dummy", address),
	};

	return i2c_new_device(adapter, &info);
}
EXPORT_SYMBOL_GPL(i2c_new_dummy);

/* ------------------------------------------------------------------------- */

/* I2C bus adapters -- one roots each I2C or SMBUS segment */

static void i2c_adapter_dev_release(struct device *dev)
{
	struct i2c_adapter *adap = to_i2c_adapter(dev);
	complete(&adap->dev_released);
}

static ssize_t
show_adapter_name(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct i2c_adapter *adap = to_i2c_adapter(dev);
	return sprintf(buf, "%s\n", adap->name);
}

static struct device_attribute i2c_adapter_attrs[] = {
	__ATTR(name, S_IRUGO, show_adapter_name, NULL),
	{ },
};

static struct class i2c_adapter_class = {
	.owner			= THIS_MODULE,
	.name			= "i2c-adapter",
	.dev_attrs		= i2c_adapter_attrs,
};

static void i2c_scan_static_board_info(struct i2c_adapter *adapter)
{
	struct i2c_devinfo	*devinfo;

	mutex_lock(&__i2c_board_lock);
	list_for_each_entry(devinfo, &__i2c_board_list, list) {
		if (devinfo->busnum == adapter->nr
				&& !i2c_new_device(adapter,
						&devinfo->board_info))
			dev_err(&adapter->dev,
				"Can't create device at 0x%02x\n",
				devinfo->board_info.addr);
	}
	mutex_unlock(&__i2c_board_lock);
}

static int i2c_do_add_adapter(struct device_driver *d, void *data)
{
	struct i2c_driver *driver = to_i2c_driver(d);
	struct i2c_adapter *adap = data;

	/* Detect supported devices on that bus, and instantiate them */
	i2c_detect(adap, driver);

	/* Let legacy drivers scan this bus for matching devices */
	if (driver->attach_adapter) {
		/* We ignore the return code; if it fails, too bad */
		driver->attach_adapter(adap);
	}
	return 0;
}

static int i2c_register_adapter(struct i2c_adapter *adap)
{
	int res = 0, dummy;

	/* Can't register until after driver model init */
	if (unlikely(WARN_ON(!i2c_bus_type.p)))
		return -EAGAIN;

	mutex_init(&adap->bus_lock);
	mutex_init(&adap->clist_lock);
	INIT_LIST_HEAD(&adap->clients);

	mutex_lock(&core_lock);

	/* Set default timeout to 1 second if not already set */
	if (adap->timeout == 0)
		adap->timeout = HZ;

	dev_set_name(&adap->dev, "i2c-%d", adap->nr);
	adap->dev.release = &i2c_adapter_dev_release;
	adap->dev.class = &i2c_adapter_class;
	res = device_register(&adap->dev);
	if (res)
		goto out_list;

	dev_dbg(&adap->dev, "adapter [%s] registered\n", adap->name);

	/* create pre-declared device nodes */
	if (adap->nr < __i2c_first_dynamic_bus_num)
		i2c_scan_static_board_info(adap);

	/* Notify drivers */
	dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
				 i2c_do_add_adapter);

out_unlock:
	mutex_unlock(&core_lock);
	return res;

out_list:
	idr_remove(&i2c_adapter_idr, adap->nr);
	goto out_unlock;
}

/**
 * i2c_add_adapter - declare i2c adapter, use dynamic bus number
 * @adapter: the adapter to add
 * Context: can sleep
 *
 * This routine is used to declare an I2C adapter when its bus number
 * doesn't matter.  Examples: for I2C adapters dynamically added by
 * USB links or PCI plugin cards.
 *
 * When this returns zero, a new bus number was allocated and stored
 * in adap->nr, and the specified adapter became available for clients.
 * Otherwise, a negative errno value is returned.
 */
int i2c_add_adapter(struct i2c_adapter *adapter)
{
	int	id, res = 0;

retry:
	if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) == 0)
		return -ENOMEM;

	mutex_lock(&core_lock);
	/* "above" here means "above or equal to", sigh */
	res = idr_get_new_above(&i2c_adapter_idr, adapter,
				__i2c_first_dynamic_bus_num, &id);
	mutex_unlock(&core_lock);

	if (res < 0) {
		if (res == -EAGAIN)
			goto retry;
		return res;
	}

	adapter->nr = id;
	return i2c_register_adapter(adapter);
}
EXPORT_SYMBOL(i2c_add_adapter);

/**
 * i2c_add_numbered_adapter - declare i2c adapter, use static bus number
 * @adap: the adapter to register (with adap->nr initialized)
 * Context: can sleep
 *
 * This routine is used to declare an I2C adapter when its bus number
 * matters.  For example, use it for I2C adapters from system-on-chip CPUs,
 * or otherwise built in to the system's mainboard, and where i2c_board_info
 * is used to properly configure I2C devices.
 *
 * If no devices have pre-been declared for this bus, then be sure to
 * register the adapter before any dynamically allocated ones.  Otherwise
 * the required bus ID may not be available.
 *
 * When this returns zero, the specified adapter became available for
 * clients using the bus number provided in adap->nr.  Also, the table
 * of I2C devices pre-declared using i2c_register_board_info() is scanned,
 * and the appropriate driver model device nodes are created.  Otherwise, a
 * negative errno value is returned.
 */
int i2c_add_numbered_adapter(struct i2c_adapter *adap)
{
	int	id;
	int	status;

	if (adap->nr & ~MAX_ID_MASK)
		return -EINVAL;

retry:
	if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) == 0)
		return -ENOMEM;

	mutex_lock(&core_lock);
	/* "above" here means "above or equal to", sigh;
	 * we need the "equal to" result to force the result
	 */
	status = idr_get_new_above(&i2c_adapter_idr, adap, adap->nr, &id);
	if (status == 0 && id != adap->nr) {
		status = -EBUSY;
		idr_remove(&i2c_adapter_idr, id);
	}
	mutex_unlock(&core_lock);
	if (status == -EAGAIN)
		goto retry;

	if (status == 0)
		status = i2c_register_adapter(adap);
	return status;
}
EXPORT_SYMBOL_GPL(i2c_add_numbered_adapter);

static int i2c_do_del_adapter(struct device_driver *d, void *data)
{
	struct i2c_driver *driver = to_i2c_driver(d);
	struct i2c_adapter *adapter = data;
	struct i2c_client *client, *_n;
	int res;

	/* Remove the devices we created ourselves as the result of hardware
	 * probing (using a driver's detect method) */
	list_for_each_entry_safe(client, _n, &driver->clients, detected) {
		if (client->adapter == adapter) {
			dev_dbg(&adapter->dev, "Removing %s at 0x%x\n",
				client->name, client->addr);
			list_del(&client->detected);
			i2c_unregister_device(client);
		}
	}

	if (!driver->detach_adapter)
		return 0;
	res = driver->detach_adapter(adapter);
	if (res)
		dev_err(&adapter->dev, "detach_adapter failed (%d) "
			"for driver [%s]\n", res, driver->driver.name);
	return res;
}

/**
 * i2c_del_adapter - unregister I2C adapter
 * @adap: the adapter being unregistered
 * Context: can sleep
 *
 * This unregisters an I2C adapter which was previously registered
 * by @i2c_add_adapter or @i2c_add_numbered_adapter.
 */
int i2c_del_adapter(struct i2c_adapter *adap)
{
	struct i2c_client *client, *_n;
	int res = 0;

	mutex_lock(&core_lock);

	/* First make sure that this adapter was ever added */
	if (idr_find(&i2c_adapter_idr, adap->nr) != adap) {
		pr_debug("i2c-core: attempting to delete unregistered "
			 "adapter [%s]\n", adap->name);
		res = -EINVAL;
		goto out_unlock;
	}

	/* Tell drivers about this removal */
	res = bus_for_each_drv(&i2c_bus_type, NULL, adap,
			       i2c_do_del_adapter);
	if (res)
		goto out_unlock;

	/* Detach any active clients */
	list_for_each_entry_safe_reverse(client, _n, &adap->clients, list) {
		i2c_unregister_device(client);
	}

	/* clean up the sysfs representation */
	init_completion(&adap->dev_released);
	device_unregister(&adap->dev);

	/* wait for sysfs to drop all references */
	wait_for_completion(&adap->dev_released);

	/* free bus id */
	idr_remove(&i2c_adapter_idr, adap->nr);

	dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);

	/* Clear the device structure in case this adapter is ever going to be
	   added again */
	memset(&adap->dev, 0, sizeof(adap->dev));

 out_unlock:
	mutex_unlock(&core_lock);
	return res;
}
EXPORT_SYMBOL(i2c_del_adapter);


/* ------------------------------------------------------------------------- */

static int __attach_adapter(struct device *dev, void *data)
{
	struct i2c_adapter *adapter = to_i2c_adapter(dev);
	struct i2c_driver *driver = data;

	i2c_detect(adapter, driver);

	/* Legacy drivers scan i2c busses directly */
	if (driver->attach_adapter)
		driver->attach_adapter(adapter);

	return 0;
}

/*
 * An i2c_driver is used with one or more i2c_client (device) nodes to access
 * i2c slave chips, on a bus instance associated with some i2c_adapter.
 */

int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
{
	int res;

	/* Can't register until after driver model init */
	if (unlikely(WARN_ON(!i2c_bus_type.p)))
		return -EAGAIN;

	/* add the driver to the list of i2c drivers in the driver core */
	driver->driver.owner = owner;
	driver->driver.bus = &i2c_bus_type;

	/* When registration returns, the driver core
	 * will have called probe() for all matching-but-unbound devices.
	 */
	res = driver_register(&driver->driver);
	if (res)
		return res;

	mutex_lock(&core_lock);

	pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);

	INIT_LIST_HEAD(&driver->clients);
	/* Walk the adapters that are already present */
	class_for_each_device(&i2c_adapter_class, NULL, driver,
			      __attach_adapter);

	mutex_unlock(&core_lock);
	return 0;
}
EXPORT_SYMBOL(i2c_register_driver);

static int __detach_adapter(struct device *dev, void *data)
{
	struct i2c_adapter *adapter = to_i2c_adapter(dev);
	struct i2c_driver *driver = data;
	struct i2c_client *client, *_n;

	/* Remove the devices we created ourselves as the result of hardware
	 * probing (using a driver's detect method) */
	list_for_each_entry_safe(client, _n, &driver->clients, detected) {
		dev_dbg(&adapter->dev, "Removing %s at 0x%x\n",
			client->name, client->addr);
		list_del(&client->detected);
		i2c_unregister_device(client);
	}

	if (is_newstyle_driver(driver))
		return 0;

	if (driver->detach_adapter) {
		if (driver->detach_adapter(adapter))
			dev_err(&adapter->dev,
				"detach_adapter failed for driver [%s]\n",
				driver->driver.name);
	}

	return 0;
}

/**
 * i2c_del_driver - unregister I2C driver
 * @driver: the driver being unregistered
 * Context: can sleep
 */
void i2c_del_driver(struct i2c_driver *driver)
{
	mutex_lock(&core_lock);

	class_for_each_device(&i2c_adapter_class, NULL, driver,
			      __detach_adapter);

	driver_unregister(&driver->driver);
	pr_debug("i2c-core: driver [%s] unregistered\n", driver->driver.name);

	mutex_unlock(&core_lock);
}
EXPORT_SYMBOL(i2c_del_driver);

/* ------------------------------------------------------------------------- */

static int __i2c_check_addr(struct device *dev, void *addrp)
{
	struct i2c_client	*client = i2c_verify_client(dev);
	int			addr = *(int *)addrp;

	if (client && client->addr == addr)
		return -EBUSY;
	return 0;
}

static int i2c_check_addr(struct i2c_adapter *adapter, int addr)
{
	return device_for_each_child(&adapter->dev, &addr, __i2c_check_addr);
}

/**
 * i2c_use_client - increments the reference count of the i2c client structure
 * @client: the client being referenced
 *
 * Each live reference to a client should be refcounted. The driver model does
 * that automatically as part of driver binding, so that most drivers don't
 * need to do this explicitly: they hold a reference until they're unbound
 * from the device.
 *
 * A pointer to the client with the incremented reference counter is returned.
 */
struct i2c_client *i2c_use_client(struct i2c_client *client)
{
	if (client && get_device(&client->dev))
		return client;
	return NULL;
}
EXPORT_SYMBOL(i2c_use_client);

/**
 * i2c_release_client - release a use of the i2c client structure
 * @client: the client being no longer referenced
 *
 * Must be called when a user of a client is finished with it.
 */
void i2c_release_client(struct i2c_client *client)
{
	if (client)
		put_device(&client->dev);
}
EXPORT_SYMBOL(i2c_release_client);

struct i2c_cmd_arg {
	unsigned	cmd;
	void		*arg;
};

static int i2c_cmd(struct device *dev, void *_arg)
{
	struct i2c_client	*client = i2c_verify_client(dev);
	struct i2c_cmd_arg	*arg = _arg;

	if (client && client->driver && client->driver->command)
		client->driver->command(client, arg->cmd, arg->arg);
	return 0;
}

void i2c_clients_command(struct i2c_adapter *adap, unsigned int cmd, void *arg)
{
	struct i2c_cmd_arg	cmd_arg;

	cmd_arg.cmd = cmd;
	cmd_arg.arg = arg;
	device_for_each_child(&adap->dev, &cmd_arg, i2c_cmd);
}
EXPORT_SYMBOL(i2c_clients_command);

static int __init i2c_init(void)
{
	int retval;

	retval = bus_register(&i2c_bus_type);
	if (retval)
		return retval;
	retval = class_register(&i2c_adapter_class);
	if (retval)
		goto bus_err;
	retval = i2c_add_driver(&dummy_driver);
	if (retval)
		goto class_err;
	return 0;

class_err:
	class_unregister(&i2c_adapter_class);
bus_err:
	bus_unregister(&i2c_bus_type);
	return retval;
}

static void __exit i2c_exit(void)
{
	i2c_del_driver(&dummy_driver);
	class_unregister(&i2c_adapter_class);
	bus_unregister(&i2c_bus_type);
}

/* We must initialize early, because some subsystems register i2c drivers
 * in subsys_initcall() code, but are linked (and initialized) before i2c.
 */
postcore_initcall(i2c_init);
module_exit(i2c_exit);

/* ----------------------------------------------------
 * the functional interface to the i2c busses.
 * ----------------------------------------------------
 */

/**
 * i2c_transfer - execute a single or combined I2C message
 * @adap: Handle to I2C bus
 * @msgs: One or more messages to execute before STOP is issued to
 *	terminate the operation; each message begins with a START.
 * @num: Number of messages to be executed.
 *
 * Returns negative errno, else the number of messages executed.
 *
 * Note that there is no requirement that each message be sent to
 * the same slave address, although that is the most common model.
 */
int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
	unsigned long orig_jiffies;
	int ret, try;

	/* REVISIT the fault reporting model here is weak:
	 *
	 *  - When we get an error after receiving N bytes from a slave,
	 *    there is no way to report "N".
	 *
	 *  - When we get a NAK after transmitting N bytes to a slave,
	 *    there is no way to report "N" ... or to let the master
	 *    continue executing the rest of this combined message, if
	 *    that's the appropriate response.
	 *
	 *  - When for example "num" is two and we successfully complete
	 *    the first message but get an error part way through the
	 *    second, it's unclear whether that should be reported as
	 *    one (discarding status on the second message) or errno
	 *    (discarding status on the first one).
	 */

	if (adap->algo->master_xfer) {
#ifdef DEBUG
		for (ret = 0; ret < num; ret++) {
			dev_dbg(&adap->dev, "master_xfer[%d] %c, addr=0x%02x, "
				"len=%d%s\n", ret, (msgs[ret].flags & I2C_M_RD)
				? 'R' : 'W', msgs[ret].addr, msgs[ret].len,
				(msgs[ret].flags & I2C_M_RECV_LEN) ? "+" : "");
		}
#endif

		if (in_atomic() || irqs_disabled()) {
			ret = mutex_trylock(&adap->bus_lock);
			if (!ret)
				/* I2C activity is ongoing. */
				return -EAGAIN;
		} else {
			mutex_lock_nested(&adap->bus_lock, adap->level);
		}

		/* Retry automatically on arbitration loss */
		orig_jiffies = jiffies;
		for (ret = 0, try = 0; try <= adap->retries; try++) {
			ret = adap->algo->master_xfer(adap, msgs, num);
			if (ret != -EAGAIN)
				break;
			if (time_after(jiffies, orig_jiffies + adap->timeout))
				break;
		}
		mutex_unlock(&adap->bus_lock);

		return ret;
	} else {
		dev_dbg(&adap->dev, "I2C level transfers not supported\n");
		return -EOPNOTSUPP;
	}
}
EXPORT_SYMBOL(i2c_transfer);

/**
 * i2c_master_send - issue a single I2C message in master transmit mode
 * @client: Handle to slave device
 * @buf: Data that will be written to the slave
 * @count: How many bytes to write
 *
 * Returns negative errno, or else the number of bytes written.
 */
int i2c_master_send(struct i2c_client *client,const char *buf ,int count)
{
	int ret;
	struct i2c_adapter *adap=client->adapter;
	struct i2c_msg msg;

	msg.addr = client->addr;
	msg.flags = client->flags & I2C_M_TEN;
	msg.len = count;
	msg.buf = (char *)buf;

	ret = i2c_transfer(adap, &msg, 1);

	/* If everything went ok (i.e. 1 msg transmitted), return #bytes
	   transmitted, else error code. */
	return (ret == 1) ? count : ret;
}
EXPORT_SYMBOL(i2c_master_send);

/**
 * i2c_master_recv - issue a single I2C message in master receive mode
 * @client: Handle to slave device
 * @buf: Where to store data read from slave
 * @count: How many bytes to read
 *
 * Returns negative errno, or else the number of bytes read.
 */
int i2c_master_recv(struct i2c_client *client, char *buf ,int count)
{
	struct i2c_adapter *adap=client->adapter;
	struct i2c_msg msg;
	int ret;

	msg.addr = client->addr;
	msg.flags = client->flags & I2C_M_TEN;
	msg.flags |= I2C_M_RD;
	msg.len = count;
	msg.buf = buf;

	ret = i2c_transfer(adap, &msg, 1);

	/* If everything went ok (i.e. 1 msg transmitted), return #bytes
	   transmitted, else error code. */
	return (ret == 1) ? count : ret;
}
EXPORT_SYMBOL(i2c_master_recv);

/* ----------------------------------------------------
 * the i2c address scanning function
 * Will not work for 10-bit addresses!
 * ----------------------------------------------------
 */

static int i2c_detect_address(struct i2c_client *temp_client, int kind,
			      struct i2c_driver *driver)
{
	struct i2c_board_info info;
	struct i2c_adapter *adapter = temp_client->adapter;
	int addr = temp_client->addr;
	int err;

	/* Make sure the address is valid */
	if (addr < 0x03 || addr > 0x77) {
		dev_warn(&adapter->dev, "Invalid probe address 0x%02x\n",
			 addr);
		return -EINVAL;
	}

	/* Skip if already in use */
	if (i2c_check_addr(adapter, addr))
		return 0;

	/* Make sure there is something at this address, unless forced */
	if (kind < 0) {
		if (i2c_smbus_xfer(adapter, addr, 0, 0, 0,
				   I2C_SMBUS_QUICK, NULL) < 0)
			return 0;

		/* prevent 24RF08 corruption */
		if ((addr & ~0x0f) == 0x50)
			i2c_smbus_xfer(adapter, addr, 0, 0, 0,
				       I2C_SMBUS_QUICK, NULL);
	}

	/* Finally call the custom detection function */
	memset(&info, 0, sizeof(struct i2c_board_info));
	info.addr = addr;
	err = driver->detect(temp_client, kind, &info);
	if (err) {
		/* -ENODEV is returned if the detection fails. We catch it
		   here as this isn't an error. */
		return err == -ENODEV ? 0 : err;
	}

	/* Consistency check */
	if (info.type[0] == '\0') {
		dev_err(&adapter->dev, "%s detection function provided "
			"no name for 0x%x\n", driver->driver.name,
			addr);
	} else {
		struct i2c_client *client;

		/* Detection succeeded, instantiate the device */
		dev_dbg(&adapter->dev, "Creating %s at 0x%02x\n",
			info.type, info.addr);
		client = i2c_new_device(adapter, &info);
		if (client)
			list_add_tail(&client->detected, &driver->clients);
		else
			dev_err(&adapter->dev, "Failed creating %s at 0x%02x\n",
				info.type, info.addr);
	}
	return 0;
}

static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver)
{
	const struct i2c_client_address_data *address_data;
	struct i2c_client *temp_client;
	int i, err = 0;
	int adap_id = i2c_adapter_id(adapter);

	address_data = driver->address_data;
	if (!driver->detect || !address_data)
		return 0;

	/* Set up a temporary client to help detect callback */
	temp_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);
	if (!temp_client)
		return -ENOMEM;
	temp_client->adapter = adapter;

	/* Force entries are done first, and are not affected by ignore
	   entries */
	if (address_data->forces) {
		const unsigned short * const *forces = address_data->forces;
		int kind;

		for (kind = 0; forces[kind]; kind++) {
			for (i = 0; forces[kind][i] != I2C_CLIENT_END;
			     i += 2) {
				if (forces[kind][i] == adap_id
				 || forces[kind][i] == ANY_I2C_BUS) {
					dev_dbg(&adapter->dev, "found force "
						"parameter for adapter %d, "
						"addr 0x%02x, kind %d\n",
						adap_id, forces[kind][i + 1],
						kind);
					temp_client->addr = forces[kind][i + 1];
					err = i2c_detect_address(temp_client,
						kind, driver);
					if (err)
						goto exit_free;
				}
			}
		}
	}

	/* Stop here if the classes do not match */
	if (!(adapter->class & driver->class))
		goto exit_free;

	/* Stop here if we can't use SMBUS_QUICK */
	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_QUICK)) {
		if (address_data->probe[0] == I2C_CLIENT_END
		 && address_data->normal_i2c[0] == I2C_CLIENT_END)
			goto exit_free;

		dev_warn(&adapter->dev, "SMBus Quick command not supported, "
			 "can't probe for chips\n");
		err = -EOPNOTSUPP;
		goto exit_free;
	}

	/* Probe entries are done second, and are not affected by ignore
	   entries either */
	for (i = 0; address_data->probe[i] != I2C_CLIENT_END; i += 2) {
		if (address_data->probe[i] == adap_id
		 || address_data->probe[i] == ANY_I2C_BUS) {
			dev_dbg(&adapter->dev, "found probe parameter for "
				"adapter %d, addr 0x%02x\n", adap_id,
				address_data->probe[i + 1]);
			temp_client->addr = address_data->probe[i + 1];
			err = i2c_detect_address(temp_client, -1, driver);
			if (err)
				goto exit_free;
		}
	}

	/* Normal entries are done last, unless shadowed by an ignore entry */
	for (i = 0; address_data->normal_i2c[i] != I2C_CLIENT_END; i += 1) {
		int j, ignore;

		ignore = 0;
		for (j = 0; address_data->ignore[j] != I2C_CLIENT_END;
		     j += 2) {
			if ((address_data->ignore[j] == adap_id ||
			     address_data->ignore[j] == ANY_I2C_BUS)
			 && address_data->ignore[j + 1]
			    == address_data->normal_i2c[i]) {
				dev_dbg(&adapter->dev, "found ignore "
					"parameter for adapter %d, "
					"addr 0x%02x\n", adap_id,
					address_data->ignore[j + 1]);
				ignore = 1;
				break;
			}
		}
		if (ignore)
			continue;

		dev_dbg(&adapter->dev, "found normal entry for adapter %d, "
			"addr 0x%02x\n", adap_id,
			address_data->normal_i2c[i]);
		temp_client->addr = address_data->normal_i2c[i];
		err = i2c_detect_address(temp_client, -1, driver);
		if (err)
			goto exit_free;
	}

 exit_free:
	kfree(temp_client);
	return err;
}

struct i2c_client *
i2c_new_probed_device(struct i2c_adapter *adap,
		      struct i2c_board_info *info,
		      unsigned short const *addr_list)
{
	int i;

	/* Stop here if the bus doesn't support probing */
	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_READ_BYTE)) {
		dev_err(&adap->dev, "Probing not supported\n");
		return NULL;
	}

	for (i = 0; addr_list[i] != I2C_CLIENT_END; i++) {
		/* Check address validity */
		if (addr_list[i] < 0x03 || addr_list[i] > 0x77) {
			dev_warn(&adap->dev, "Invalid 7-bit address "
				 "0x%02x\n", addr_list[i]);
			continue;
		}

		/* Check address availability */
		if (i2c_check_addr(adap, addr_list[i])) {
			dev_dbg(&adap->dev, "Address 0x%02x already in "
				"use, not probing\n", addr_list[i]);
			continue;
		}

		/* Test address responsiveness
		   The default probe method is a quick write, but it is known
		   to corrupt the 24RF08 EEPROMs due to a state machine bug,
		   and could also irreversibly write-protect some EEPROMs, so
		   for address ranges 0x30-0x37 and 0x50-0x5f, we use a byte
		   read instead. Also, some bus drivers don't implement
		   quick write, so we fallback to a byte read it that case
		   too. */
		if ((addr_list[i] & ~0x07) == 0x30
		 || (addr_list[i] & ~0x0f) == 0x50
		 || !i2c_check_functionality(adap, I2C_FUNC_SMBUS_QUICK)) {
			union i2c_smbus_data data;

			if (i2c_smbus_xfer(adap, addr_list[i], 0,
					   I2C_SMBUS_READ, 0,
					   I2C_SMBUS_BYTE, &data) >= 0)
				break;
		} else {
			if (i2c_smbus_xfer(adap, addr_list[i], 0,
					   I2C_SMBUS_WRITE, 0,
					   I2C_SMBUS_QUICK, NULL) >= 0)
				break;
		}
	}

	if (addr_list[i] == I2C_CLIENT_END) {
		dev_dbg(&adap->dev, "Probing failed, no device found\n");
		return NULL;
	}

	info->addr = addr_list[i];
	return i2c_new_device(adap, info);
}
EXPORT_SYMBOL_GPL(i2c_new_probed_device);

struct i2c_adapter* i2c_get_adapter(int id)
{
	struct i2c_adapter *adapter;

	mutex_lock(&core_lock);
	adapter = idr_find(&i2c_adapter_idr, id);
	if (adapter && !try_module_get(adapter->owner))
		adapter = NULL;

	mutex_unlock(&core_lock);
	return adapter;
}
EXPORT_SYMBOL(i2c_get_adapter);

void i2c_put_adapter(struct i2c_adapter *adap)
{
	module_put(adap->owner);
}
EXPORT_SYMBOL(i2c_put_adapter);

/* The SMBus parts */

#define POLY    (0x1070U << 3)
static u8 crc8(u16 data)
{
	int i;

	for(i = 0; i < 8; i++) {
		if (data & 0x8000)
			data = data ^ POLY;
		data = data << 1;
	}
	return (u8)(data >> 8);
}

/* Incremental CRC8 over count bytes in the array pointed to by p */
static u8 i2c_smbus_pec(u8 crc, u8 *p, size_t count)
{
	int i;

	for(i = 0; i < count; i++)
		crc = crc8((crc ^ p[i]) << 8);
	return crc;
}

/* Assume a 7-bit address, which is reasonable for SMBus */
static u8 i2c_smbus_msg_pec(u8 pec, struct i2c_msg *msg)
{
	/* The address will be sent first */
	u8 addr = (msg->addr << 1) | !!(msg->flags & I2C_M_RD);
	pec = i2c_smbus_pec(pec, &addr, 1);

	/* The data buffer follows */
	return i2c_smbus_pec(pec, msg->buf, msg->len);
}

/* Used for write only transactions */
static inline void i2c_smbus_add_pec(struct i2c_msg *msg)
{
	msg->buf[msg->len] = i2c_smbus_msg_pec(0, msg);
	msg->len++;
}

/* Return <0 on CRC error
   If there was a write before this read (most cases) we need to take the
   partial CRC from the write part into account.
   Note that this function does modify the message (we need to decrease the
   message length to hide the CRC byte from the caller). */
static int i2c_smbus_check_pec(u8 cpec, struct i2c_msg *msg)
{
	u8 rpec = msg->buf[--msg->len];
	cpec = i2c_smbus_msg_pec(cpec, msg);

	if (rpec != cpec) {
		pr_debug("i2c-core: Bad PEC 0x%02x vs. 0x%02x\n",
			rpec, cpec);
		return -EBADMSG;
	}
	return 0;
}

/**
 * i2c_smbus_read_byte - SMBus "receive byte" protocol
 * @client: Handle to slave device
 *
 * This executes the SMBus "receive byte" protocol, returning negative errno
 * else the byte received from the device.
 */
s32 i2c_smbus_read_byte(struct i2c_client *client)
{
	union i2c_smbus_data data;
	int status;

	status = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
				I2C_SMBUS_READ, 0,
				I2C_SMBUS_BYTE, &data);
	return (status < 0) ? status : data.byte;
}
EXPORT_SYMBOL(i2c_smbus_read_byte);

/**
 * i2c_smbus_write_byte - SMBus "send byte" protocol
 * @client: Handle to slave device
 * @value: Byte to be sent
 *
 * This executes the SMBus "send byte" protocol, returning negative errno
 * else zero on success.
 */
s32 i2c_smbus_write_byte(struct i2c_client *client, u8 value)
{
	return i2c_smbus_xfer(client->adapter,client->addr,client->flags,
	                      I2C_SMBUS_WRITE, value, I2C_SMBUS_BYTE, NULL);
}
EXPORT_SYMBOL(i2c_smbus_write_byte);

/**
 * i2c_smbus_read_byte_data - SMBus "read byte" protocol
 * @client: Handle to slave device
 * @command: Byte interpreted by slave
 *
 * This executes the SMBus "read byte" protocol, returning negative errno
 * else a data byte received from the device.
 */
s32 i2c_smbus_read_byte_data(struct i2c_client *client, u8 command)
{
	union i2c_smbus_data data;
	int status;

	status = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
				I2C_SMBUS_READ, command,
				I2C_SMBUS_BYTE_DATA, &data);
	return (status < 0) ? status : data.byte;
}
EXPORT_SYMBOL(i2c_smbus_read_byte_data);

/**
 * i2c_smbus_write_byte_data - SMBus "write byte" protocol
 * @client: Handle to slave device
 * @command: Byte interpreted by slave
 * @value: Byte being written
 *
 * This executes the SMBus "write byte" protocol, returning negative errno
 * else zero on success.
 */
s32 i2c_smbus_write_byte_data(struct i2c_client *client, u8 command, u8 value)
{
	union i2c_smbus_data data;
	data.byte = value;
	return i2c_smbus_xfer(client->adapter,client->addr,client->flags,
	                      I2C_SMBUS_WRITE,command,
	                      I2C_SMBUS_BYTE_DATA,&data);
}
EXPORT_SYMBOL(i2c_smbus_write_byte_data);

/**
 * i2c_smbus_read_word_data - SMBus "read word" protocol
 * @client: Handle to slave device
 * @command: Byte interpreted by slave
 *
 * This executes the SMBus "read word" protocol, returning negative errno
 * else a 16-bit unsigned "word" received from the device.
 */
s32 i2c_smbus_read_word_data(struct i2c_client *client, u8 command)
{
	union i2c_smbus_data data;
	int status;

	status = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
				I2C_SMBUS_READ, command,
				I2C_SMBUS_WORD_DATA, &data);
	return (status < 0) ? status : data.word;
}
EXPORT_SYMBOL(i2c_smbus_read_word_data);

/**
 * i2c_smbus_write_word_data - SMBus "write word" protocol
 * @client: Handle to slave device
 * @command: Byte interpreted by slave
 * @value: 16-bit "word" being written
 *
 * This executes the SMBus "write word" protocol, returning negative errno
 * else zero on success.
 */
s32 i2c_smbus_write_word_data(struct i2c_client *client, u8 command, u16 value)
{
	union i2c_smbus_data data;
	data.word = value;
	return i2c_smbus_xfer(client->adapter,client->addr,client->flags,
	                      I2C_SMBUS_WRITE,command,
	                      I2C_SMBUS_WORD_DATA,&data);
}
EXPORT_SYMBOL(i2c_smbus_write_word_data);

/**
 * i2c_smbus_process_call - SMBus "process call" protocol
 * @client: Handle to slave device
 * @command: Byte interpreted by slave
 * @value: 16-bit "word" being written
 *
 * This executes the SMBus "process call" protocol, returning negative errno
 * else a 16-bit unsigned "word" received from the device.
 */
s32 i2c_smbus_process_call(struct i2c_client *client, u8 command, u16 value)
{
	union i2c_smbus_data data;
	int status;
	data.word = value;

	status = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
				I2C_SMBUS_WRITE, command,
				I2C_SMBUS_PROC_CALL, &data);
	return (status < 0) ? status : data.word;
}
EXPORT_SYMBOL(i2c_smbus_process_call);

/**
 * i2c_smbus_read_block_data - SMBus "block read" protocol
 * @client: Handle to slave device
 * @command: Byte interpreted by slave
 * @values: Byte array into which data will be read; big enough to hold
 *	the data returned by the slave.  SMBus allows at most 32 bytes.
 *
 * This executes the SMBus "block read" protocol, returning negative errno
 * else the number of data bytes in the slave's response.
 *
 * Note that using this function requires that the client's adapter support
 * the I2C_FUNC_SMBUS_READ_BLOCK_DATA functionality.  Not all adapter drivers
 * support this; its emulation through I2C messaging relies on a specific
 * mechanism (I2C_M_RECV_LEN) which may not be implemented.
 */
s32 i2c_smbus_read_block_data(struct i2c_client *client, u8 command,
			      u8 *values)
{
	union i2c_smbus_data data;
	int status;

	status = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
				I2C_SMBUS_READ, command,
				I2C_SMBUS_BLOCK_DATA, &data);
	if (status)
		return status;

	memcpy(values, &data.block[1], data.block[0]);
	return data.block[0];
}
EXPORT_SYMBOL(i2c_smbus_read_block_data);

/**
 * i2c_smbus_write_block_data - SMBus "block write" protocol
 * @client: Handle to slave device
 * @command: Byte interpreted by slave
 * @length: Size of data block; SMBus allows at most 32 bytes
 * @values: Byte array which will be written.
 *
 * This executes the SMBus "block write" protocol, returning negative errno
 * else zero on success.
 */
s32 i2c_smbus_write_block_data(struct i2c_client *client, u8 command,
			       u8 length, const u8 *values)
{
	union i2c_smbus_data data;

	if (length > I2C_SMBUS_BLOCK_MAX)
		length = I2C_SMBUS_BLOCK_MAX;
	data.block[0] = length;
	memcpy(&data.block[1], values, length);
	return i2c_smbus_xfer(client->adapter,client->addr,client->flags,
			      I2C_SMBUS_WRITE,command,
			      I2C_SMBUS_BLOCK_DATA,&data);
}
EXPORT_SYMBOL(i2c_smbus_write_block_data);

/* Returns the number of read bytes */
s32 i2c_smbus_read_i2c_block_data(struct i2c_client *client, u8 command,
				  u8 length, u8 *values)
{
	union i2c_smbus_data data;
	int status;

	if (length > I2C_SMBUS_BLOCK_MAX)
		length = I2C_SMBUS_BLOCK_MAX;
	data.block[0] = length;
	status = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
				I2C_SMBUS_READ, command,
				I2C_SMBUS_I2C_BLOCK_DATA, &data);
	if (status < 0)
		return status;

	memcpy(values, &data.block[1], data.block[0]);
	return data.block[0];
}
EXPORT_SYMBOL(i2c_smbus_read_i2c_block_data);

s32 i2c_smbus_write_i2c_block_data(struct i2c_client *client, u8 command,
				   u8 length, const u8 *values)
{
	union i2c_smbus_data data;

	if (length > I2C_SMBUS_BLOCK_MAX)
		length = I2C_SMBUS_BLOCK_MAX;
	data.block[0] = length;
	memcpy(data.block + 1, values, length);
	return i2c_smbus_xfer(client->adapter, client->addr, client->flags,
			      I2C_SMBUS_WRITE, command,
			      I2C_SMBUS_I2C_BLOCK_DATA, &data);
}
EXPORT_SYMBOL(i2c_smbus_write_i2c_block_data);

/* Simulate a SMBus command using the i2c protocol
   No checking of parameters is done!  */
static s32 i2c_smbus_xfer_emulated(struct i2c_adapter * adapter, u16 addr,
                                   unsigned short flags,
                                   char read_write, u8 command, int size,
                                   union i2c_smbus_data * data)
{
	/* So we need to generate a series of msgs. In the case of writing, we
	  need to use only one message; when reading, we need two. We initialize
	  most things with sane defaults, to keep the code below somewhat
	  simpler. */
	unsigned char msgbuf0[I2C_SMBUS_BLOCK_MAX+3];
	unsigned char msgbuf1[I2C_SMBUS_BLOCK_MAX+2];
	int num = read_write == I2C_SMBUS_READ?2:1;
	struct i2c_msg msg[2] = { { addr, flags, 1, msgbuf0 },
	                          { addr, flags | I2C_M_RD, 0, msgbuf1 }
	                        };
	int i;
	u8 partial_pec = 0;
	int status;

	msgbuf0[0] = command;
	switch(size) {
	case I2C_SMBUS_QUICK:
		msg[0].len = 0;
		/* Special case: The read/write field is used as data */
		msg[0].flags = flags | (read_write == I2C_SMBUS_READ ?
					I2C_M_RD : 0);
		num = 1;
		break;
	case I2C_SMBUS_BYTE:
		if (read_write == I2C_SMBUS_READ) {
			/* Special case: only a read! */
			msg[0].flags = I2C_M_RD | flags;
			num = 1;
		}
		break;
	case I2C_SMBUS_BYTE_DATA:
		if (read_write == I2C_SMBUS_READ)
			msg[1].len = 1;
		else {
			msg[0].len = 2;
			msgbuf0[1] = data->byte;
		}
		break;
	case I2C_SMBUS_WORD_DATA:
		if (read_write == I2C_SMBUS_READ)
			msg[1].len = 2;
		else {
			msg[0].len=3;
			msgbuf0[1] = data->word & 0xff;
			msgbuf0[2] = data->word >> 8;
		}
		break;
	case I2C_SMBUS_PROC_CALL:
		num = 2; /* Special case */
		read_write = I2C_SMBUS_READ;
		msg[0].len = 3;
		msg[1].len = 2;
		msgbuf0[1] = data->word & 0xff;
		msgbuf0[2] = data->word >> 8;
		break;
	case I2C_SMBUS_BLOCK_DATA:
		if (read_write == I2C_SMBUS_READ) {
			msg[1].flags |= I2C_M_RECV_LEN;
			msg[1].len = 1; /* block length will be added by
					   the underlying bus driver */
		} else {
			msg[0].len = data->block[0] + 2;
			if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 2) {
				dev_err(&adapter->dev,
					"Invalid block write size %d\n",
					data->block[0]);
				return -EINVAL;
			}
			for (i = 1; i < msg[0].len; i++)
				msgbuf0[i] = data->block[i-1];
		}
		break;
	case I2C_SMBUS_BLOCK_PROC_CALL:
		num = 2; /* Another special case */
		read_write = I2C_SMBUS_READ;
		if (data->block[0] > I2C_SMBUS_BLOCK_MAX) {
			dev_err(&adapter->dev,
				"Invalid block write size %d\n",
				data->block[0]);
			return -EINVAL;
		}
		msg[0].len = data->block[0] + 2;
		for (i = 1; i < msg[0].len; i++)
			msgbuf0[i] = data->block[i-1];
		msg[1].flags |= I2C_M_RECV_LEN;
		msg[1].len = 1; /* block length will be added by
				   the underlying bus driver */
		break;
	case I2C_SMBUS_I2C_BLOCK_DATA:
		if (read_write == I2C_SMBUS_READ) {
			msg[1].len = data->block[0];
		} else {
			msg[0].len = data->block[0] + 1;
			if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 1) {
				dev_err(&adapter->dev,
					"Invalid block write size %d\n",
					data->block[0]);
				return -EINVAL;
			}
			for (i = 1; i <= data->block[0]; i++)
				msgbuf0[i] = data->block[i];
		}
		break;
	default:
		dev_err(&adapter->dev, "Unsupported transaction %d\n", size);
		return -EOPNOTSUPP;
	}

	i = ((flags & I2C_CLIENT_PEC) && size != I2C_SMBUS_QUICK
				      && size != I2C_SMBUS_I2C_BLOCK_DATA);
	if (i) {
		/* Compute PEC if first message is a write */
		if (!(msg[0].flags & I2C_M_RD)) {
			if (num == 1) /* Write only */
				i2c_smbus_add_pec(&msg[0]);
			else /* Write followed by read */
				partial_pec = i2c_smbus_msg_pec(0, &msg[0]);
		}
		/* Ask for PEC if last message is a read */
		if (msg[num-1].flags & I2C_M_RD)
			msg[num-1].len++;
	}

	status = i2c_transfer(adapter, msg, num);
	if (status < 0)
		return status;

	/* Check PEC if last message is a read */
	if (i && (msg[num-1].flags & I2C_M_RD)) {
		status = i2c_smbus_check_pec(partial_pec, &msg[num-1]);
		if (status < 0)
			return status;
	}

	if (read_write == I2C_SMBUS_READ)
		switch(size) {
			case I2C_SMBUS_BYTE:
				data->byte = msgbuf0[0];
				break;
			case I2C_SMBUS_BYTE_DATA:
				data->byte = msgbuf1[0];
				break;
			case I2C_SMBUS_WORD_DATA:
			case I2C_SMBUS_PROC_CALL:
				data->word = msgbuf1[0] | (msgbuf1[1] << 8);
				break;
			case I2C_SMBUS_I2C_BLOCK_DATA:
				for (i = 0; i < data->block[0]; i++)
					data->block[i+1] = msgbuf1[i];
				break;
			case I2C_SMBUS_BLOCK_DATA:
			case I2C_SMBUS_BLOCK_PROC_CALL:
				for (i = 0; i < msgbuf1[0] + 1; i++)
					data->block[i] = msgbuf1[i];
				break;
		}
	return 0;
}

/**
 * i2c_smbus_xfer - execute SMBus protocol operations
 * @adapter: Handle to I2C bus
 * @addr: Address of SMBus slave on that bus
 * @flags: I2C_CLIENT_* flags (usually zero or I2C_CLIENT_PEC)
 * @read_write: I2C_SMBUS_READ or I2C_SMBUS_WRITE
 * @command: Byte interpreted by slave, for protocols which use such bytes
 * @protocol: SMBus protocol operation to execute, such as I2C_SMBUS_PROC_CALL
 * @data: Data to be read or written
 *
 * This executes an SMBus protocol operation, and returns a negative
 * errno code else zero on success.
 */
s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags,
		   char read_write, u8 command, int protocol,
		   union i2c_smbus_data *data)
{
	unsigned long orig_jiffies;
	int try;
	s32 res;

	flags &= I2C_M_TEN | I2C_CLIENT_PEC;

	if (adapter->algo->smbus_xfer) {
		mutex_lock(&adapter->bus_lock);

		/* Retry automatically on arbitration loss */
		orig_jiffies = jiffies;
		for (res = 0, try = 0; try <= adapter->retries; try++) {
			res = adapter->algo->smbus_xfer(adapter, addr, flags,
							read_write, command,
							protocol, data);
			if (res != -EAGAIN)
				break;
			if (time_after(jiffies,
				       orig_jiffies + adapter->timeout))
				break;
		}
		mutex_unlock(&adapter->bus_lock);
	} else
		res = i2c_smbus_xfer_emulated(adapter,addr,flags,read_write,
					      command, protocol, data);

	return res;
}
EXPORT_SYMBOL(i2c_smbus_xfer);

MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
MODULE_DESCRIPTION("I2C-Bus main module");
MODULE_LICENSE("GPL");