drivers/i2c/i2c-mux.c - linux - Git at Google

 /*
  * Multiplexed I2C bus driver.
  *
  * Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
  * Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
  * Copyright (c) 2009-2010 NSN GmbH & Co KG <michael.lawnick.ext@nsn.com>
  *
  * Simplifies access to complex multiplexed I2C bus topologies, by presenting
  * each multiplexed bus segment as an additional I2C adapter.
  * Supports multi-level mux'ing (mux behind a mux).
  *
  * Based on:
  *	i2c-virt.c from Kumar Gala <galak@kernel.crashing.org>
  *	i2c-virtual.c from Ken Harrenstien, Copyright (c) 2004 Google, Inc.
  *	i2c-virtual.c from Brian Kuschak <bkuschak@yahoo.com>
  *
  * This file is licensed under the terms of the GNU General Public
  * License version 2. This program is licensed "as is" without any
  * warranty of any kind, whether express or implied.
  */

 #include <linux/acpi.h>
 #include <linux/i2c.h>
 #include <linux/i2c-mux.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/slab.h>

 /* multiplexer per channel data */
 struct i2c_mux_priv {
 	struct i2c_adapter adap;
 	struct i2c_algorithm algo;
 	struct i2c_mux_core *muxc;
 	u32 chan_id;
 };

 static int __i2c_mux_master_xfer(struct i2c_adapter *adap,
 				 struct i2c_msg msgs[], int num)
 {
 	struct i2c_mux_priv *priv = adap->algo_data;
 	struct i2c_mux_core *muxc = priv->muxc;
 	struct i2c_adapter *parent = muxc->parent;
 	int ret;

 	/* Switch to the right mux port and perform the transfer. */

 	ret = muxc->select(muxc, priv->chan_id);
 	if (ret >= 0)
 		ret = __i2c_transfer(parent, msgs, num);
 	if (muxc->deselect)
 		muxc->deselect(muxc, priv->chan_id);

 	return ret;
 }

 static int i2c_mux_master_xfer(struct i2c_adapter *adap,
 			       struct i2c_msg msgs[], int num)
 {
 	struct i2c_mux_priv *priv = adap->algo_data;
 	struct i2c_mux_core *muxc = priv->muxc;
 	struct i2c_adapter *parent = muxc->parent;
 	int ret;

 	/* Switch to the right mux port and perform the transfer. */

 	ret = muxc->select(muxc, priv->chan_id);
 	if (ret >= 0)
 		ret = i2c_transfer(parent, msgs, num);
 	if (muxc->deselect)
 		muxc->deselect(muxc, priv->chan_id);

 	return ret;
 }

 static int __i2c_mux_smbus_xfer(struct i2c_adapter *adap,
 				u16 addr, unsigned short flags,
 				char read_write, u8 command,
 				int size, union i2c_smbus_data *data)
 {
 	struct i2c_mux_priv *priv = adap->algo_data;
 	struct i2c_mux_core *muxc = priv->muxc;
 	struct i2c_adapter *parent = muxc->parent;
 	int ret;

 	/* Select the right mux port and perform the transfer. */

 	ret = muxc->select(muxc, priv->chan_id);
 	if (ret >= 0)
 		ret = parent->algo->smbus_xfer(parent, addr, flags,
 					read_write, command, size, data);
 	if (muxc->deselect)
 		muxc->deselect(muxc, priv->chan_id);

 	return ret;
 }

 static int i2c_mux_smbus_xfer(struct i2c_adapter *adap,
 			      u16 addr, unsigned short flags,
 			      char read_write, u8 command,
 			      int size, union i2c_smbus_data *data)
 {
 	struct i2c_mux_priv *priv = adap->algo_data;
 	struct i2c_mux_core *muxc = priv->muxc;
 	struct i2c_adapter *parent = muxc->parent;
 	int ret;

 	/* Select the right mux port and perform the transfer. */

 	ret = muxc->select(muxc, priv->chan_id);
 	if (ret >= 0)
 		ret = i2c_smbus_xfer(parent, addr, flags,
 				     read_write, command, size, data);
 	if (muxc->deselect)
 		muxc->deselect(muxc, priv->chan_id);

 	return ret;
 }

 /* Return the parent's functionality */
 static u32 i2c_mux_functionality(struct i2c_adapter *adap)
 {
 	struct i2c_mux_priv *priv = adap->algo_data;
 	struct i2c_adapter *parent = priv->muxc->parent;

 	return parent->algo->functionality(parent);
 }

 /* Return all parent classes, merged */
 static unsigned int i2c_mux_parent_classes(struct i2c_adapter *parent)
 {
 	unsigned int class = 0;

 	do {
 		class |= parent->class;
 		parent = i2c_parent_is_i2c_adapter(parent);
 	} while (parent);

 	return class;
 }

 static void i2c_mux_lock_bus(struct i2c_adapter *adapter, unsigned int flags)
 {
 	struct i2c_mux_priv *priv = adapter->algo_data;
 	struct i2c_adapter *parent = priv->muxc->parent;

 	rt_mutex_lock_nested(&parent->mux_lock, i2c_adapter_depth(adapter));
 	if (!(flags & I2C_LOCK_ROOT_ADAPTER))
 		return;
 	i2c_lock_bus(parent, flags);
 }

 static int i2c_mux_trylock_bus(struct i2c_adapter *adapter, unsigned int flags)
 {
 	struct i2c_mux_priv *priv = adapter->algo_data;
 	struct i2c_adapter *parent = priv->muxc->parent;

 	if (!rt_mutex_trylock(&parent->mux_lock))
 		return 0;	/* mux_lock not locked, failure */
 	if (!(flags & I2C_LOCK_ROOT_ADAPTER))
 		return 1;	/* we only want mux_lock, success */
 	if (i2c_trylock_bus(parent, flags))
 		return 1;	/* parent locked too, success */
 	rt_mutex_unlock(&parent->mux_lock);
 	return 0;		/* parent not locked, failure */
 }

 static void i2c_mux_unlock_bus(struct i2c_adapter *adapter, unsigned int flags)
 {
 	struct i2c_mux_priv *priv = adapter->algo_data;
 	struct i2c_adapter *parent = priv->muxc->parent;

 	if (flags & I2C_LOCK_ROOT_ADAPTER)
 		i2c_unlock_bus(parent, flags);
 	rt_mutex_unlock(&parent->mux_lock);
 }

 static void i2c_parent_lock_bus(struct i2c_adapter *adapter,
 				unsigned int flags)
 {
 	struct i2c_mux_priv *priv = adapter->algo_data;
 	struct i2c_adapter *parent = priv->muxc->parent;

 	rt_mutex_lock_nested(&parent->mux_lock, i2c_adapter_depth(adapter));
 	i2c_lock_bus(parent, flags);
 }

 static int i2c_parent_trylock_bus(struct i2c_adapter *adapter,
 				  unsigned int flags)
 {
 	struct i2c_mux_priv *priv = adapter->algo_data;
 	struct i2c_adapter *parent = priv->muxc->parent;

 	if (!rt_mutex_trylock(&parent->mux_lock))
 		return 0;	/* mux_lock not locked, failure */
 	if (i2c_trylock_bus(parent, flags))
 		return 1;	/* parent locked too, success */
 	rt_mutex_unlock(&parent->mux_lock);
 	return 0;		/* parent not locked, failure */
 }

 static void i2c_parent_unlock_bus(struct i2c_adapter *adapter,
 				  unsigned int flags)
 {
 	struct i2c_mux_priv *priv = adapter->algo_data;
 	struct i2c_adapter *parent = priv->muxc->parent;

 	i2c_unlock_bus(parent, flags);
 	rt_mutex_unlock(&parent->mux_lock);
 }

 struct i2c_adapter *i2c_root_adapter(struct device *dev)
 {
 	struct device *i2c;
 	struct i2c_adapter *i2c_root;

 	/*
 	 * Walk up the device tree to find an i2c adapter, indicating
 	 * that this is an i2c client device. Check all ancestors to
 	 * handle mfd devices etc.
 	 */
 	for (i2c = dev; i2c; i2c = i2c->parent) {
 		if (i2c->type == &i2c_adapter_type)
 			break;
 	}
 	if (!i2c)
 		return NULL;

 	/* Continue up the tree to find the root i2c adapter */
 	i2c_root = to_i2c_adapter(i2c);
 	while (i2c_parent_is_i2c_adapter(i2c_root))
 		i2c_root = i2c_parent_is_i2c_adapter(i2c_root);

 	return i2c_root;
 }
 EXPORT_SYMBOL_GPL(i2c_root_adapter);

 struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
 				   struct device *dev, int max_adapters,
 				   int sizeof_priv, u32 flags,
 				   int (*select)(struct i2c_mux_core *, u32),
 				   int (*deselect)(struct i2c_mux_core *, u32))
 {
 	struct i2c_mux_core *muxc;

 	muxc = devm_kzalloc(dev, sizeof(*muxc)
 			    + max_adapters * sizeof(muxc->adapter[0])
 			    + sizeof_priv, GFP_KERNEL);
 	if (!muxc)
 		return NULL;
 	if (sizeof_priv)
 		muxc->priv = &muxc->adapter[max_adapters];

 	muxc->parent = parent;
 	muxc->dev = dev;
 	if (flags & I2C_MUX_LOCKED)
 		muxc->mux_locked = true;
 	if (flags & I2C_MUX_ARBITRATOR)
 		muxc->arbitrator = true;
 	if (flags & I2C_MUX_GATE)
 		muxc->gate = true;
 	muxc->select = select;
 	muxc->deselect = deselect;
 	muxc->max_adapters = max_adapters;

 	return muxc;
 }
 EXPORT_SYMBOL_GPL(i2c_mux_alloc);

 static const struct i2c_lock_operations i2c_mux_lock_ops = {
 	.lock_bus =    i2c_mux_lock_bus,
 	.trylock_bus = i2c_mux_trylock_bus,
 	.unlock_bus =  i2c_mux_unlock_bus,
 };

 static const struct i2c_lock_operations i2c_parent_lock_ops = {
 	.lock_bus =    i2c_parent_lock_bus,
 	.trylock_bus = i2c_parent_trylock_bus,
 	.unlock_bus =  i2c_parent_unlock_bus,
 };

 int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 			u32 force_nr, u32 chan_id,
 			unsigned int class)
 {
 	struct i2c_adapter *parent = muxc->parent;
 	struct i2c_mux_priv *priv;
 	char symlink_name[20];
 	int ret;

 	if (muxc->num_adapters >= muxc->max_adapters) {
 		dev_err(muxc->dev, "No room for more i2c-mux adapters\n");
 		return -EINVAL;
 	}

 	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 	if (!priv)
 		return -ENOMEM;

 	/* Set up private adapter data */
 	priv->muxc = muxc;
 	priv->chan_id = chan_id;

 	/* Need to do algo dynamically because we don't know ahead
 	 * of time what sort of physical adapter we'll be dealing with.
 	 */
 	if (parent->algo->master_xfer) {
 		if (muxc->mux_locked)
 			priv->algo.master_xfer = i2c_mux_master_xfer;
 		else
 			priv->algo.master_xfer = __i2c_mux_master_xfer;
 	}
 	if (parent->algo->smbus_xfer) {
 		if (muxc->mux_locked)
 			priv->algo.smbus_xfer = i2c_mux_smbus_xfer;
 		else
 			priv->algo.smbus_xfer = __i2c_mux_smbus_xfer;
 	}
 	priv->algo.functionality = i2c_mux_functionality;

 	/* Now fill out new adapter structure */
 	snprintf(priv->adap.name, sizeof(priv->adap.name),
 		 "i2c-%d-mux (chan_id %d)", i2c_adapter_id(parent), chan_id);
 	priv->adap.owner = THIS_MODULE;
 	priv->adap.algo = &priv->algo;
 	priv->adap.algo_data = priv;
 	priv->adap.dev.parent = &parent->dev;
 	priv->adap.retries = parent->retries;
 	priv->adap.timeout = parent->timeout;
 	priv->adap.quirks = parent->quirks;
 	if (muxc->mux_locked)
 		priv->adap.lock_ops = &i2c_mux_lock_ops;
 	else
 		priv->adap.lock_ops = &i2c_parent_lock_ops;

 	/* Sanity check on class */
 	if (i2c_mux_parent_classes(parent) & class)
 		dev_err(&parent->dev,
 			"Segment %d behind mux can't share classes with ancestors\n",
 			chan_id);
 	else
 		priv->adap.class = class;

 	/*
 	 * Try to populate the mux adapter's of_node, expands to
 	 * nothing if !CONFIG_OF.
 	 */
 	if (muxc->dev->of_node) {
 		struct device_node *dev_node = muxc->dev->of_node;
 		struct device_node *mux_node, *child = NULL;
 		u32 reg;

 		if (muxc->arbitrator)
 			mux_node = of_get_child_by_name(dev_node, "i2c-arb");
 		else if (muxc->gate)
 			mux_node = of_get_child_by_name(dev_node, "i2c-gate");
 		else
 			mux_node = of_get_child_by_name(dev_node, "i2c-mux");

 		if (mux_node) {
 			/* A "reg" property indicates an old-style DT entry */
 			if (!of_property_read_u32(mux_node, "reg", &reg)) {
 				of_node_put(mux_node);
 				mux_node = NULL;
 			}
 		}

 		if (!mux_node)
 			mux_node = of_node_get(dev_node);
 		else if (muxc->arbitrator || muxc->gate)
 			child = of_node_get(mux_node);

 		if (!child) {
 			for_each_child_of_node(mux_node, child) {
 				ret = of_property_read_u32(child, "reg", &reg);
 				if (ret)
 					continue;
 				if (chan_id == reg)
 					break;
 			}
 		}

 		priv->adap.dev.of_node = child;
 		of_node_put(mux_node);
 	}

 	/*
 	 * Associate the mux channel with an ACPI node.
 	 */
 	if (has_acpi_companion(muxc->dev))
 		acpi_preset_companion(&priv->adap.dev,
 				      ACPI_COMPANION(muxc->dev),
 				      chan_id);

 	if (force_nr) {
 		priv->adap.nr = force_nr;
 		ret = i2c_add_numbered_adapter(&priv->adap);
 		if (ret < 0) {
 			dev_err(&parent->dev,
 				"failed to add mux-adapter %u as bus %u (error=%d)\n",
 				chan_id, force_nr, ret);
 			goto err_free_priv;
 		}
 	} else {
 		ret = i2c_add_adapter(&priv->adap);
 		if (ret < 0) {
 			dev_err(&parent->dev,
 				"failed to add mux-adapter %u (error=%d)\n",
 				chan_id, ret);
 			goto err_free_priv;
 		}
 	}

 	WARN(sysfs_create_link(&priv->adap.dev.kobj, &muxc->dev->kobj,
 			       "mux_device"),
 	     "can't create symlink to mux device\n");

 	snprintf(symlink_name, sizeof(symlink_name), "channel-%u", chan_id);
 	WARN(sysfs_create_link(&muxc->dev->kobj, &priv->adap.dev.kobj,
 			       symlink_name),
 	     "can't create symlink to channel %u\n", chan_id);
 	dev_info(&parent->dev, "Added multiplexed i2c bus %d\n",
 		 i2c_adapter_id(&priv->adap));

 	muxc->adapter[muxc->num_adapters++] = &priv->adap;
 	return 0;

 err_free_priv:
 	kfree(priv);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(i2c_mux_add_adapter);

 void i2c_mux_del_adapters(struct i2c_mux_core *muxc)
 {
 	char symlink_name[20];

 	while (muxc->num_adapters) {
 		struct i2c_adapter *adap = muxc->adapter[--muxc->num_adapters];
 		struct i2c_mux_priv *priv = adap->algo_data;
 		struct device_node *np = adap->dev.of_node;

 		muxc->adapter[muxc->num_adapters] = NULL;

 		snprintf(symlink_name, sizeof(symlink_name),
 			 "channel-%u", priv->chan_id);
 		sysfs_remove_link(&muxc->dev->kobj, symlink_name);

 		sysfs_remove_link(&priv->adap.dev.kobj, "mux_device");
 		i2c_del_adapter(adap);
 		of_node_put(np);
 		kfree(priv);
 	}
 }
 EXPORT_SYMBOL_GPL(i2c_mux_del_adapters);

 MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
 MODULE_DESCRIPTION("I2C driver for multiplexed I2C busses");
 MODULE_LICENSE("GPL v2");
	/*
	* Multiplexed I2C bus driver.
	*
	* Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
	* Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
	* Copyright (c) 2009-2010 NSN GmbH & Co KG <michael.lawnick.ext@nsn.com>
	*
	* Simplifies access to complex multiplexed I2C bus topologies, by presenting
	* each multiplexed bus segment as an additional I2C adapter.
	* Supports multi-level mux'ing (mux behind a mux).
	*
	* Based on:
	* i2c-virt.c from Kumar Gala <galak@kernel.crashing.org>
	* i2c-virtual.c from Ken Harrenstien, Copyright (c) 2004 Google, Inc.
	* i2c-virtual.c from Brian Kuschak <bkuschak@yahoo.com>
	*
	* This file is licensed under the terms of the GNU General Public
	* License version 2. This program is licensed "as is" without any
	* warranty of any kind, whether express or implied.
	*/

	#include <linux/acpi.h>
	#include <linux/i2c.h>
	#include <linux/i2c-mux.h>
	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/of.h>
	#include <linux/slab.h>

	/* multiplexer per channel data */
	struct i2c_mux_priv {
	struct i2c_adapter adap;
	struct i2c_algorithm algo;
	struct i2c_mux_core *muxc;
	u32 chan_id;
	};

	static int __i2c_mux_master_xfer(struct i2c_adapter *adap,
	struct i2c_msg msgs[], int num)
	{
	struct i2c_mux_priv *priv = adap->algo_data;
	struct i2c_mux_core *muxc = priv->muxc;
	struct i2c_adapter *parent = muxc->parent;
	int ret;

	/* Switch to the right mux port and perform the transfer. */

	ret = muxc->select(muxc, priv->chan_id);
	if (ret >= 0)
	ret = __i2c_transfer(parent, msgs, num);
	if (muxc->deselect)
	muxc->deselect(muxc, priv->chan_id);

	return ret;
	}

	static int i2c_mux_master_xfer(struct i2c_adapter *adap,
	struct i2c_msg msgs[], int num)
	{
	struct i2c_mux_priv *priv = adap->algo_data;
	struct i2c_mux_core *muxc = priv->muxc;
	struct i2c_adapter *parent = muxc->parent;
	int ret;

	/* Switch to the right mux port and perform the transfer. */

	ret = muxc->select(muxc, priv->chan_id);
	if (ret >= 0)
	ret = i2c_transfer(parent, msgs, num);
	if (muxc->deselect)
	muxc->deselect(muxc, priv->chan_id);

	return ret;
	}

	static int __i2c_mux_smbus_xfer(struct i2c_adapter *adap,
	u16 addr, unsigned short flags,
	char read_write, u8 command,
	int size, union i2c_smbus_data *data)
	{
	struct i2c_mux_priv *priv = adap->algo_data;
	struct i2c_mux_core *muxc = priv->muxc;
	struct i2c_adapter *parent = muxc->parent;
	int ret;

	/* Select the right mux port and perform the transfer. */

	ret = muxc->select(muxc, priv->chan_id);
	if (ret >= 0)
	ret = parent->algo->smbus_xfer(parent, addr, flags,
	read_write, command, size, data);
	if (muxc->deselect)
	muxc->deselect(muxc, priv->chan_id);

	return ret;
	}

	static int i2c_mux_smbus_xfer(struct i2c_adapter *adap,
	u16 addr, unsigned short flags,
	char read_write, u8 command,
	int size, union i2c_smbus_data *data)
	{
	struct i2c_mux_priv *priv = adap->algo_data;
	struct i2c_mux_core *muxc = priv->muxc;
	struct i2c_adapter *parent = muxc->parent;
	int ret;

	/* Select the right mux port and perform the transfer. */

	ret = muxc->select(muxc, priv->chan_id);
	if (ret >= 0)
	ret = i2c_smbus_xfer(parent, addr, flags,
	read_write, command, size, data);
	if (muxc->deselect)
	muxc->deselect(muxc, priv->chan_id);

	return ret;
	}

	/* Return the parent's functionality */
	static u32 i2c_mux_functionality(struct i2c_adapter *adap)
	{
	struct i2c_mux_priv *priv = adap->algo_data;
	struct i2c_adapter *parent = priv->muxc->parent;

	return parent->algo->functionality(parent);
	}

	/* Return all parent classes, merged */
	static unsigned int i2c_mux_parent_classes(struct i2c_adapter *parent)
	{
	unsigned int class = 0;

	do {
	class \|= parent->class;
	parent = i2c_parent_is_i2c_adapter(parent);
	} while (parent);

	return class;
	}

	static void i2c_mux_lock_bus(struct i2c_adapter *adapter, unsigned int flags)
	{
	struct i2c_mux_priv *priv = adapter->algo_data;
	struct i2c_adapter *parent = priv->muxc->parent;

	rt_mutex_lock_nested(&parent->mux_lock, i2c_adapter_depth(adapter));
	if (!(flags & I2C_LOCK_ROOT_ADAPTER))
	return;
	i2c_lock_bus(parent, flags);
	}

	static int i2c_mux_trylock_bus(struct i2c_adapter *adapter, unsigned int flags)
	{
	struct i2c_mux_priv *priv = adapter->algo_data;
	struct i2c_adapter *parent = priv->muxc->parent;

	if (!rt_mutex_trylock(&parent->mux_lock))
	return 0; /* mux_lock not locked, failure */
	if (!(flags & I2C_LOCK_ROOT_ADAPTER))
	return 1; /* we only want mux_lock, success */
	if (i2c_trylock_bus(parent, flags))
	return 1; /* parent locked too, success */
	rt_mutex_unlock(&parent->mux_lock);
	return 0; /* parent not locked, failure */
	}

	static void i2c_mux_unlock_bus(struct i2c_adapter *adapter, unsigned int flags)
	{
	struct i2c_mux_priv *priv = adapter->algo_data;
	struct i2c_adapter *parent = priv->muxc->parent;

	if (flags & I2C_LOCK_ROOT_ADAPTER)
	i2c_unlock_bus(parent, flags);
	rt_mutex_unlock(&parent->mux_lock);
	}

	static void i2c_parent_lock_bus(struct i2c_adapter *adapter,
	unsigned int flags)
	{
	struct i2c_mux_priv *priv = adapter->algo_data;
	struct i2c_adapter *parent = priv->muxc->parent;

	rt_mutex_lock_nested(&parent->mux_lock, i2c_adapter_depth(adapter));
	i2c_lock_bus(parent, flags);
	}

	static int i2c_parent_trylock_bus(struct i2c_adapter *adapter,
	unsigned int flags)
	{
	struct i2c_mux_priv *priv = adapter->algo_data;
	struct i2c_adapter *parent = priv->muxc->parent;

	if (!rt_mutex_trylock(&parent->mux_lock))
	return 0; /* mux_lock not locked, failure */
	if (i2c_trylock_bus(parent, flags))
	return 1; /* parent locked too, success */
	rt_mutex_unlock(&parent->mux_lock);
	return 0; /* parent not locked, failure */
	}

	static void i2c_parent_unlock_bus(struct i2c_adapter *adapter,
	unsigned int flags)
	{
	struct i2c_mux_priv *priv = adapter->algo_data;
	struct i2c_adapter *parent = priv->muxc->parent;

	i2c_unlock_bus(parent, flags);
	rt_mutex_unlock(&parent->mux_lock);
	}

	struct i2c_adapter i2c_root_adapter(struct device dev)
	{
	struct device *i2c;
	struct i2c_adapter *i2c_root;

	/*
	* Walk up the device tree to find an i2c adapter, indicating
	* that this is an i2c client device. Check all ancestors to
	* handle mfd devices etc.
	*/
	for (i2c = dev; i2c; i2c = i2c->parent) {
	if (i2c->type == &i2c_adapter_type)
	break;
	}
	if (!i2c)
	return NULL;

	/* Continue up the tree to find the root i2c adapter */
	i2c_root = to_i2c_adapter(i2c);
	while (i2c_parent_is_i2c_adapter(i2c_root))
	i2c_root = i2c_parent_is_i2c_adapter(i2c_root);

	return i2c_root;
	}
	EXPORT_SYMBOL_GPL(i2c_root_adapter);

	struct i2c_mux_core i2c_mux_alloc(struct i2c_adapter parent,
	struct device *dev, int max_adapters,
	int sizeof_priv, u32 flags,
	int (select)(struct i2c_mux_core , u32),
	int (deselect)(struct i2c_mux_core , u32))
	{
	struct i2c_mux_core *muxc;

	muxc = devm_kzalloc(dev, sizeof(*muxc)
	+ max_adapters * sizeof(muxc->adapter[0])
	+ sizeof_priv, GFP_KERNEL);
	if (!muxc)
	return NULL;
	if (sizeof_priv)
	muxc->priv = &muxc->adapter[max_adapters];

	muxc->parent = parent;
	muxc->dev = dev;
	if (flags & I2C_MUX_LOCKED)
	muxc->mux_locked = true;
	if (flags & I2C_MUX_ARBITRATOR)
	muxc->arbitrator = true;
	if (flags & I2C_MUX_GATE)
	muxc->gate = true;
	muxc->select = select;
	muxc->deselect = deselect;
	muxc->max_adapters = max_adapters;

	return muxc;
	}
	EXPORT_SYMBOL_GPL(i2c_mux_alloc);

	static const struct i2c_lock_operations i2c_mux_lock_ops = {
	.lock_bus = i2c_mux_lock_bus,
	.trylock_bus = i2c_mux_trylock_bus,
	.unlock_bus = i2c_mux_unlock_bus,
	};

	static const struct i2c_lock_operations i2c_parent_lock_ops = {
	.lock_bus = i2c_parent_lock_bus,
	.trylock_bus = i2c_parent_trylock_bus,
	.unlock_bus = i2c_parent_unlock_bus,
	};

	int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
	u32 force_nr, u32 chan_id,
	unsigned int class)
	{
	struct i2c_adapter *parent = muxc->parent;
	struct i2c_mux_priv *priv;
	char symlink_name[20];
	int ret;

	if (muxc->num_adapters >= muxc->max_adapters) {
	dev_err(muxc->dev, "No room for more i2c-mux adapters\n");
	return -EINVAL;
	}

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv)
	return -ENOMEM;

	/* Set up private adapter data */
	priv->muxc = muxc;
	priv->chan_id = chan_id;

	/* Need to do algo dynamically because we don't know ahead
	* of time what sort of physical adapter we'll be dealing with.
	*/
	if (parent->algo->master_xfer) {
	if (muxc->mux_locked)
	priv->algo.master_xfer = i2c_mux_master_xfer;
	else
	priv->algo.master_xfer = __i2c_mux_master_xfer;
	}
	if (parent->algo->smbus_xfer) {
	if (muxc->mux_locked)
	priv->algo.smbus_xfer = i2c_mux_smbus_xfer;
	else
	priv->algo.smbus_xfer = __i2c_mux_smbus_xfer;
	}
	priv->algo.functionality = i2c_mux_functionality;

	/* Now fill out new adapter structure */
	snprintf(priv->adap.name, sizeof(priv->adap.name),
	"i2c-%d-mux (chan_id %d)", i2c_adapter_id(parent), chan_id);
	priv->adap.owner = THIS_MODULE;
	priv->adap.algo = &priv->algo;
	priv->adap.algo_data = priv;
	priv->adap.dev.parent = &parent->dev;
	priv->adap.retries = parent->retries;
	priv->adap.timeout = parent->timeout;
	priv->adap.quirks = parent->quirks;
	if (muxc->mux_locked)
	priv->adap.lock_ops = &i2c_mux_lock_ops;
	else
	priv->adap.lock_ops = &i2c_parent_lock_ops;

	/* Sanity check on class */
	if (i2c_mux_parent_classes(parent) & class)
	dev_err(&parent->dev,
	"Segment %d behind mux can't share classes with ancestors\n",
	chan_id);
	else
	priv->adap.class = class;

	/*
	* Try to populate the mux adapter's of_node, expands to
	* nothing if !CONFIG_OF.
	*/
	if (muxc->dev->of_node) {
	struct device_node *dev_node = muxc->dev->of_node;
	struct device_node mux_node, child = NULL;
	u32 reg;

	if (muxc->arbitrator)
	mux_node = of_get_child_by_name(dev_node, "i2c-arb");
	else if (muxc->gate)
	mux_node = of_get_child_by_name(dev_node, "i2c-gate");
	else
	mux_node = of_get_child_by_name(dev_node, "i2c-mux");

	if (mux_node) {
	/* A "reg" property indicates an old-style DT entry */
	if (!of_property_read_u32(mux_node, "reg", &reg)) {
	of_node_put(mux_node);
	mux_node = NULL;
	}
	}

	if (!mux_node)
	mux_node = of_node_get(dev_node);
	else if (muxc->arbitrator \|\| muxc->gate)
	child = of_node_get(mux_node);

	if (!child) {
	for_each_child_of_node(mux_node, child) {
	ret = of_property_read_u32(child, "reg", &reg);
	if (ret)
	continue;
	if (chan_id == reg)
	break;
	}
	}

	priv->adap.dev.of_node = child;
	of_node_put(mux_node);
	}

	/*
	* Associate the mux channel with an ACPI node.
	*/
	if (has_acpi_companion(muxc->dev))
	acpi_preset_companion(&priv->adap.dev,
	ACPI_COMPANION(muxc->dev),
	chan_id);

	if (force_nr) {
	priv->adap.nr = force_nr;
	ret = i2c_add_numbered_adapter(&priv->adap);
	if (ret < 0) {
	dev_err(&parent->dev,
	"failed to add mux-adapter %u as bus %u (error=%d)\n",
	chan_id, force_nr, ret);
	goto err_free_priv;
	}
	} else {
	ret = i2c_add_adapter(&priv->adap);
	if (ret < 0) {
	dev_err(&parent->dev,
	"failed to add mux-adapter %u (error=%d)\n",
	chan_id, ret);
	goto err_free_priv;
	}
	}

	WARN(sysfs_create_link(&priv->adap.dev.kobj, &muxc->dev->kobj,
	"mux_device"),
	"can't create symlink to mux device\n");

	snprintf(symlink_name, sizeof(symlink_name), "channel-%u", chan_id);
	WARN(sysfs_create_link(&muxc->dev->kobj, &priv->adap.dev.kobj,
	symlink_name),
	"can't create symlink to channel %u\n", chan_id);
	dev_info(&parent->dev, "Added multiplexed i2c bus %d\n",
	i2c_adapter_id(&priv->adap));

	muxc->adapter[muxc->num_adapters++] = &priv->adap;
	return 0;

	err_free_priv:
	kfree(priv);
	return ret;
	}
	EXPORT_SYMBOL_GPL(i2c_mux_add_adapter);

	void i2c_mux_del_adapters(struct i2c_mux_core *muxc)
	{
	char symlink_name[20];

	while (muxc->num_adapters) {
	struct i2c_adapter *adap = muxc->adapter[--muxc->num_adapters];
	struct i2c_mux_priv *priv = adap->algo_data;
	struct device_node *np = adap->dev.of_node;

	muxc->adapter[muxc->num_adapters] = NULL;

	snprintf(symlink_name, sizeof(symlink_name),
	"channel-%u", priv->chan_id);
	sysfs_remove_link(&muxc->dev->kobj, symlink_name);

	sysfs_remove_link(&priv->adap.dev.kobj, "mux_device");
	i2c_del_adapter(adap);
	of_node_put(np);
	kfree(priv);
	}
	}
	EXPORT_SYMBOL_GPL(i2c_mux_del_adapters);

	MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
	MODULE_DESCRIPTION("I2C driver for multiplexed I2C busses");
	MODULE_LICENSE("GPL v2");