Re: [PATCH v2 1/2] i2c: Multiplexed I2C bus core support

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

Hi Michael,

On Tue, 04 May 2010 14:46:57 +0200, Michael Lawnick wrote:
> Add multiplexed bus core support. I2C multiplexer and switches
> like pca954x get instantiated as new adapters per output.
> 
> Signed-off-by: Michael Lawnick <ml.lawnick-Mmb7MZpHnFY@public.gmane.org>
> 
> ---
> Based on kernel 2.6.33 +
> [PATCH] i2c-core: Use per-adapter userspace device lists
> by Jean Delware <20100424201914.08b3f008-ig7AzVSIIG7kN2dkZ6Wm7A@public.gmane.org>
> <http://article.gmane.org/gmane.linux.drivers.i2c/5994/>

Future patches should be based on 2.6.34 at least... 2.6.35-rc2 would
be even better.

Review follows. Need some more work I fear, but not that much... Please
let me know if you are going to submit another iteration, or if you
prefer to let me fix things the way I like (in which case I'll still
ask you to test my version of the patch when I'm done.)

> 
>  drivers/i2c/Kconfig     |    8 ++
>  drivers/i2c/Makefile    |    1 +
>  drivers/i2c/i2c-core.c  |   93 ++++++++++++++++++++++--
>  drivers/i2c/i2c-dev.c   |   46 ++++++++++++-
>  drivers/i2c/i2c-mux.c   |  184 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/i2c-mux.h |   46 ++++++++++++
>  include/linux/i2c.h     |   11 +++
>  7 files changed, 381 insertions(+), 8 deletions(-)
>  create mode 100755 drivers/i2c/i2c-mux.c
>  create mode 100755 include/linux/i2c-mux.h
> 
> diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
> index 8d8a00e..2cd6d78 100755
> --- a/drivers/i2c/Kconfig
> +++ b/drivers/i2c/Kconfig
> @@ -36,6 +36,14 @@ config I2C_COMPAT
>  	  other user-space package which expects i2c adapters to be class
>  	  devices. If you don't know, say Y.
>  
> +config I2C_MUX
> +	tristate "I2C bus multiplexing support"
> +	depends on I2C

Dependency on I2C isn't needed: this configuration item is already
in an "if I2C" block. A dependency on EXPERIMENTAL might be a good idea
for the time being though.

> +	help
> +	  Say Y here if you want the I2C core to support the ability to
> +	  handle multiplexed I2C bus topologies, by presenting each
> +	  multiplexed segment as a I2C adapter.

For support that can be build as a module, we usually add a sentence
saying so and giving the name of the module.

> +

I would move config I2C_MUX below config I2C_CHARDEV, to make it
consistent with Makefile, and also because users expect new options to
be added after existing options.

>  config I2C_CHARDEV
>  	tristate "I2C device interface"
>  	help
> diff --git a/drivers/i2c/Makefile b/drivers/i2c/Makefile
> index ba26e6c..a488e8b 100755
> --- a/drivers/i2c/Makefile
> +++ b/drivers/i2c/Makefile
> @@ -5,6 +5,7 @@
>  obj-$(CONFIG_I2C_BOARDINFO)	+= i2c-boardinfo.o
>  obj-$(CONFIG_I2C)		+= i2c-core.o
>  obj-$(CONFIG_I2C_CHARDEV)	+= i2c-dev.o
> +obj-$(CONFIG_I2C_MUX)		+= i2c-mux.o
>  obj-y				+= busses/ chips/ algos/
>  
>  ifeq ($(CONFIG_I2C_DEBUG_CORE),y)
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index fc93e28..682966a 100755
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -20,7 +20,10 @@
>  /* With some changes from Kyösti Mälkki <kmalkki-kf+aQKke1yb1KXRcyAk9cg@public.gmane.org>.
>     All SMBus-related things are written by Frodo Looijaard <frodol@dds.nl>
>     SMBus 2.0 support by Mark Studebaker <mdsxyz123-/E1597aS9LQAvxtiuMwx3w@public.gmane.org> and
> -   Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org> */
> +   Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
> +   Mux support by Rodolfo Giometti <giometti-AVVDYK/kqiJWk0Htik3J/w@public.gmane.org> and
> +   Michael Lawnick <michael.lawnick.ext-OYasijW0DpE@public.gmane.org> */
> +

Extra blank line.

>  
>  #include <linux/module.h>
>  #include <linux/kernel.h>
> @@ -288,6 +291,12 @@ struct i2c_client *i2c_verify_client(struct device *dev)
>  }
>  EXPORT_SYMBOL(i2c_verify_client);
>  
> +static int i2c_parent_is_i2c_adapter(const struct i2c_adapter *adapter)
> +{
> +	return adapter->dev.parent != NULL
> +		&& adapter->dev.parent->bus == &i2c_bus_type;
> +}
> +
>  
>  /**
>   * i2c_new_device - instantiate an i2c device
> @@ -624,6 +633,7 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
>  
>  	rt_mutex_init(&adap->bus_lock);
>  	INIT_LIST_HEAD(&adap->userspace_clients);
> +	INIT_LIST_HEAD(&adap->mux_list_head);
>  
>  	/* Set default timeout to 1 second if not already set */
>  	if (adap->timeout == 0)
> @@ -949,9 +959,78 @@ static int __i2c_check_addr(struct device *dev, void *addrp)
>  	return 0;
>  }
>  
> +/* walk up mux tree */
> +static int i2c_check_mux_parents(struct i2c_adapter *adapter, int addr)
> +{
> +	int	result;
> +
> +	result = device_for_each_child(&adapter->dev, &addr, __i2c_check_addr);
> +
> +	if (!result && i2c_parent_is_i2c_adapter(adapter))
> +		result = i2c_check_mux_parents(
> +				    to_i2c_adapter(adapter->dev.parent), addr);
> +
> +	return result;
> +}
> +
> +/* recurse down mux tree */
> +static int i2c_check_mux_childs(struct i2c_adapter *adapter, int addr)

"childs" doesn't exist in proper English, the right work is "children" ;)

> +{
> +	int			result = 0;
> +	struct i2c_adapter	*child, *next;
> +
> +	list_for_each_entry_safe(child, next, &adapter->mux_list_head,
> +							 mux_list) {
> +		result = device_for_each_child(&child->dev, &addr,
> +							     __i2c_check_addr);
> +		if (result)
> +			break;
> +		result = i2c_check_mux_childs(child, addr);

This value is ignored, except for the last child. I think you should
break here too.

> +	}
> +	return result;
> +}
> +
>  static int i2c_check_addr(struct i2c_adapter *adapter, int addr)
>  {
> -	return device_for_each_child(&adapter->dev, &addr, __i2c_check_addr);
> +	int	result;
> +
> +	result = i2c_check_mux_parents(adapter, addr);
> +
> +	if (!result)
> +		result = i2c_check_mux_childs(adapter, addr);
> +
> +	return result;
> +}

I am worried about (the lack of) locking when the above function is
called. The problem isn't new with your patch, but your patch makes it
worse: beforehand, the driver core would complain if we hit a race
here, because we would try to create two clients with the same bus_id as
a result. But now, we may create 2 conflicting clients with different
bus_id, so the driver core will not complain.

I'll think about it some more, and add locking if needed.

> +static void i2c_mux_tree_lock(struct i2c_adapter *adap)
> +{
> +	if (i2c_parent_is_i2c_adapter(adap))
> +		i2c_mux_tree_lock(to_i2c_adapter(adap->dev.parent));
> +	else
> +		i2c_lock_adapter(adap);
> +}
> +
> +static int i2c_mux_tree_trylock(struct i2c_adapter *adap)
> +{
> +	int			ret;
> +	struct i2c_adapter	*parent;
> +
> +	if (i2c_parent_is_i2c_adapter(adap)) {
> +		parent = to_i2c_adapter(adap->dev.parent);
> +		ret = i2c_mux_tree_trylock(parent);
> +	} else {
> +		ret = i2c_trylock_adapter(adap);
> +	}
> +
> +	return ret;
> +}
> +
> +static void i2c_mux_tree_unlock(struct i2c_adapter *adap)
> +{
> +	if (i2c_parent_is_i2c_adapter(adap))
> +		i2c_mux_tree_unlock(to_i2c_adapter(adap->dev.parent));
> +	else
> +		i2c_unlock_adapter(adap);
>  }
>  
>  /**
> @@ -1104,12 +1183,12 @@ int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>  #endif
>  
>  		if (in_atomic() || irqs_disabled()) {
> -			ret = rt_mutex_trylock(&adap->bus_lock);
> +			ret = i2c_mux_tree_trylock(adap);
>  			if (!ret)
>  				/* I2C activity is ongoing. */
>  				return -EAGAIN;
>  		} else {
> -			rt_mutex_lock(&adap->bus_lock);
> +			i2c_mux_tree_lock(adap);
>  		}
>  
>  		/* Retry automatically on arbitration loss */
> @@ -1121,7 +1200,7 @@ int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>  			if (time_after(jiffies, orig_jiffies + adap->timeout))
>  				break;
>  		}
> -		rt_mutex_unlock(&adap->bus_lock);
> +		i2c_mux_tree_unlock(adap);
>  
>  		return ret;
>  	} else {
> @@ -1857,7 +1936,7 @@ s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags,
>  	flags &= I2C_M_TEN | I2C_CLIENT_PEC;
>  
>  	if (adapter->algo->smbus_xfer) {
> -		rt_mutex_lock(&adapter->bus_lock);
> +		i2c_mux_tree_lock(adapter);
>  
>  		/* Retry automatically on arbitration loss */
>  		orig_jiffies = jiffies;
> @@ -1871,7 +1950,7 @@ s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags,
>  				       orig_jiffies + adapter->timeout))
>  				break;
>  		}
> -		rt_mutex_unlock(&adapter->bus_lock);
> +		i2c_mux_tree_unlock(adapter);
>  	} else
>  		res = i2c_smbus_xfer_emulated(adapter,addr,flags,read_write,
>  					      command, protocol, data);

I'm worried that this approach is risky. We now use i2c_mux_tree_*lock
internally, but still expose the i2c_*lock_adapter() API externally.
This API is _not_ mux-aware, and will do the wrong thing if called on a
bus segment behind a mux.

I'd rather not have two APIs when we really only need one. Let's just
update the current public API to be mux-aware, and use that everywhere.

> diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
> index f4110aa..da5327f 100755
> --- a/drivers/i2c/i2c-dev.c
> +++ b/drivers/i2c/i2c-dev.c
> @@ -193,12 +193,56 @@ static int i2cdev_check(struct device *dev, void *addrp)
>  	return dev->driver ? -EBUSY : 0;
>  }
>  
> +static int i2cdev_parent_is_i2c_adapter(const struct i2c_adapter *adapter)
> +{
> +	return adapter->dev.parent != NULL
> +		&& adapter->dev.parent->bus == &i2c_bus_type;
> +}

This is an exact duplicate of the same function in i2c-core. I'd rather
make it an inline function in <linux/i2c.h>, or export the one from
i2c-core.c. We have enough duplicate code in i2c-dev.c already :(

> +
> +/* walk up mux tree */
> +static int i2cdev_check_mux_parents(struct i2c_adapter *adapter, int addr)
> +{
> +	int result;
> +
> +	result = device_for_each_child(&adapter->dev, &addr, i2cdev_check);
> +
> +	if (!result && i2cdev_parent_is_i2c_adapter(adapter))
> +		result = i2cdev_check_mux_parents(
> +				    to_i2c_adapter(adapter->dev.parent), addr);
> +
> +	return result;
> +}
> +
> +/* recurse down mux tree */
> +static int i2cdev_check_mux_childs(struct i2c_adapter *adapter, int addr)

children

> +{
> +	int result = 0;
> +	struct i2c_adapter *child, *next;
> +
> +	list_for_each_entry_safe(child, next, &adapter->mux_list_head,
> +				 mux_list) {
> +		result = device_for_each_child(&child->dev, &addr,
> +					       i2cdev_check);
> +		if (result)
> +			break;
> +		result = i2cdev_check_mux_childs(child, addr);

Same as in the i2c-core variant, this value is ignored, I think this
isn't correct.

> +	}
> +	return result;
> +}
> +
>  /* This address checking function differs from the one in i2c-core
>     in that it considers an address with a registered device, but no
>     driver bound to it, as NOT busy. */
>  static int i2cdev_check_addr(struct i2c_adapter *adapter, unsigned int addr)
>  {
> -	return device_for_each_child(&adapter->dev, &addr, i2cdev_check);
> +	int result;
> +
> +	result = i2cdev_check_mux_parents(adapter, addr);
> +
> +	if (!result)
> +		result = i2cdev_check_mux_childs(adapter, addr);
> +
> +	return result;
>  }
>  
>  static noinline int i2cdev_ioctl_rdrw(struct i2c_client *client,
> diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
> new file mode 100755
> index 0000000..f88d29a
> --- /dev/null
> +++ b/drivers/i2c/i2c-mux.c
> @@ -0,0 +1,184 @@
> +/*
> + * Multiplexed I2C bus driver.
> + *
> + * Copyright (c) 2008-2009 Rodolfo Giometti <giometti-k2GhghHVRtY@public.gmane.org>
> + * Copyright (c) 2008-2009 Eurotech S.p.A. <info-ymFC7zkAqBI1GQ1Ptb7lUw@public.gmane.org>
> + *
> + * 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-XVmvHMARGAS8U2dJNN8I7kB+6BGkLq7r@public.gmane.org>
> + *	i2c-virtual.c from Ken Harrenstien, Copyright (c) 2004 Google, Inc.
> + *	i2c-virtual.c from Brian Kuschak <bkuschak-/E1597aS9LQAvxtiuMwx3w@public.gmane.org>
> + *
> + * 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.
> + */
> +
> +/* Adapted to kernel 2.6.33 by Michael Lawnick <michael.lawnick.ext@nsn.com> */

I'd rather have you add your copyright with the other ones already
present above.

> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/i2c.h>
> +#include <linux/i2c-mux.h>
> +
> +/* multiplexer per channel data */
> +struct i2c_mux_priv {
> +	struct i2c_adapter adap;
> +	struct i2c_algorithm algo;
> +
> +	struct i2c_adapter *parent;
> +	void *mux_dev;	/* the mux chip/device */
> +	u32  chan_id;	/* the channel id */
> +
> +	int (*select)(struct i2c_adapter *adap, void *mux_dev, u32 chan_id);
> +	int (*deselect)(struct i2c_adapter *adap, void *mux_dev, u32 chan_id);

The two "adap" can go away... I insisted on having parameter names for
the other two; for structures, it's usually pretty clear what we're
talking about.

> +};
> +
> +#define VIRT_TIMEOUT		(HZ/2)
> +#define VIRT_RETRIES		3

These two are no longer used and can thus be deleted.

> +
> +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_adapter *parent = priv->parent;
> +	int ret;
> +
> +	/* Switch to the right mux port and perform the transfer.*/

Missing space at end of comment.

> +
> +	ret = priv->select(parent, priv->mux_dev, priv->chan_id);
> +	if (ret >= 0)
> +		ret = parent->algo->master_xfer(parent, msgs, num);
> +	if (priv->deselect)
> +		priv->deselect(parent, priv->mux_dev, 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_adapter *parent = priv->parent;
> +	int ret;
> +
> +	/* Select the right mux port and perform the transfer.*/

Ditto.

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

Strange alignment.

> +	if (priv->deselect)
> +		priv->deselect(parent, priv->mux_dev, priv->chan_id);
> +
> +	return ret;
> +}
> +
> +/* Return the parent's functionality for the virtual adapter */

Please avoid referring to "virtual adapters". The fact here is that all
bus segments of a given tree share the same functionality, because it
is a characteristic of the controller - nothing virtual here.

> +static u32 i2c_mux_functionality(struct i2c_adapter *adap)
> +{
> +	struct i2c_mux_priv *priv = adap->algo_data;
> +	struct i2c_adapter *parent = priv->parent;
> +
> +	return parent->algo->functionality(parent);
> +}
> +
> +struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
> +				void *mux_dev, u32 force_nr, u32 chan_id,
> +				int (*select) (struct i2c_adapter *,
> +					       void *, u32),
> +				int (*deselect) (struct i2c_adapter *,
> +						 void *, u32))
> +{
> +	struct i2c_mux_priv *priv;
> +	int ret;
> +
> +	priv = kzalloc(sizeof(struct i2c_mux_priv), GFP_KERNEL);
> +	if (!priv)
> +		return NULL;
> +
> +	/* Set up private adapter data */
> +	priv->parent = parent;
> +	priv->mux_dev = mux_dev;
> +	priv->chan_id = chan_id;
> +	priv->select = select;
> +	priv->deselect = deselect;
> +
> +	/* 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)
> +		priv->algo.master_xfer = i2c_mux_master_xfer;
> +	if (parent->algo->smbus_xfer)
> +		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);

I'm only half happy with this name. One problem is that it isn't
unique: if you have 2 mux chips on the same root segment, this will
lead to duplicate segments with the same name. Another problem is that
it completely hides the name of the controller (which, I admit, we may
recover by walking sysfs, but still...)

This isn't a blocker point, but something to keep in mind for further
improvements. It might even make sense to let the caller provide the
format for the segment names.

> +	priv->adap.owner = THIS_MODULE;
> +	priv->adap.id = parent->id;
> +	priv->adap.algo = &priv->algo;
> +	priv->adap.algo_data = priv;
> +	priv->adap.dev.parent = &parent->dev;
> +
> +	if (force_nr) {
> +		priv->adap.nr = force_nr;
> +		ret = i2c_add_numbered_adapter(&priv->adap);
> +	} else {
> +		ret = i2c_add_adapter(&priv->adap);
> +	}
> +	if (ret < 0) {
> +		dev_err(&parent->dev, "failed to add mux-adapter (error=%d)\n",
> +			ret);
> +		kfree(priv);
> +		return NULL;
> +	}
> +
> +	list_add_tail(&priv->adap.mux_list, &parent->mux_list_head);

The driver core maintains a device tree already, do you really need to
keep your own? We've tried hard to remove all redundancy between
i2c-core and the driver core in the last couple years, so I really would
like us to not add such redundancy back now.

If you have a good reason to have your own list, please explain. If
not, please get rid of it.

> +
> +	dev_info(&parent->dev, "i2c-mux-%d: Multiplexed I2C bus on "
> +		"parent bus i2c-%d, chan_id %d\n",
> +		i2c_adapter_id(&priv->adap), i2c_adapter_id(parent), chan_id);

Have you looked at the output? I expect some redundancy, as you use
dev_info() on the parent, i2c_adapter_id(parent) is already included. I
think I'd rather call dev_info() on the newly spawned child, so you can
get rid of the leading "i2c-mux-%d". BTW, please use dev_name() instead
of hard-coding i2c-%d for the parent.

> +
> +	return &priv->adap;
> +}
> +EXPORT_SYMBOL_GPL(i2c_add_mux_adapter);
> +
> +int i2c_del_mux_adapter(struct i2c_adapter *adap)
> +{
> +	struct i2c_mux_priv *priv = adap->algo_data;
> +	int ret;
> +	struct i2c_adapter *child, *next, *parent;

Would look nicer with all structs in front and ret last, IMHO.

> +
> +	if (adap->dev.parent != NULL
> +		&& adap->dev.parent->bus == &i2c_bus_type) {

This is a copy of i2c_parent_is_i2c_adapter(), isn't it? That's one
more reason to export it from i2c-core.

> +		parent = to_i2c_adapter(adap->dev.parent);

Note that we could have i2c_parent_is_i2c_adapter() return the parent
adapter, if it proves useful in practice.

> +		list_for_each_entry_safe(child, next, &parent->mux_list_head,
> +					 mux_list) {
> +			if (child == adap) {
> +				list_del(&child->mux_list);
> +				break;
> +			}
> +		}
> +	}

That being said... Using the driver core's list would save you the
hassle altogether.

> +
> +	ret = i2c_del_adapter(adap);
> +	if (ret < 0)
> +		return ret;
> +	kfree(priv);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(i2c_del_mux_adapter);
> +
> +MODULE_AUTHOR("Rodolfo Giometti <giometti-k2GhghHVRtY@public.gmane.org>");
> +MODULE_DESCRIPTION("I2C driver for multiplexed I2C busses");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/i2c-mux.h b/include/linux/i2c-mux.h
> new file mode 100755
> index 0000000..0d5d6c8
> --- /dev/null
> +++ b/include/linux/i2c-mux.h
> @@ -0,0 +1,46 @@
> +/*
> + *
> + * i2c-mux.h - functions for the i2c-bus mux support
> + *
> + * Copyright (c) 2008-2009 Rodolfo Giometti <giometti-k2GhghHVRtY@public.gmane.org>
> + * Copyright (c) 2008-2009 Eurotech S.p.A. <info-ymFC7zkAqBI1GQ1Ptb7lUw@public.gmane.org>
> + * Michael Lawnick <michael.lawnick.ext-OYasijW0DpE@public.gmane.org>
> + *
> + * 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.
> + */
> +
> +#ifndef _LINUX_I2C_MUX_H
> +#define _LINUX_I2C_MUX_H
> +
> +#ifdef __KERNEL__
> +
> +/*
> + * Called to create a i2c bus on a multiplexed bus segment.
> + * The mux_dev and chan_id parameters are passed to the select
> + * and deselect callback functions to perform hardware-specific
> + * mux control.
> + */
> +struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
> +				void *mux_dev, u32 force_nr, u32 chan_id,
> +				int (*select) (struct i2c_adapter *adap,
> +					       void *mux_dev, u32 chan_id),
> +				int (*deselect) (struct i2c_adapter *,
> +						 void *mux_dev, u32 chan_id));
> +
> +int i2c_del_mux_adapter(struct i2c_adapter *adap);
> +
> +#endif /* __KERNEL__ */
> +
> +#endif /* _LINUX_I2C_H */

You actually mean /* _LINUX_I2C_MUX_H */.

> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 1fd7b12..898a8c1 100755
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -349,6 +349,8 @@ struct i2c_adapter {
>  	struct completion dev_released;
>  
>  	struct list_head userspace_clients;
> +	struct list_head mux_list_head;
> +	struct list_head mux_list;

As said before, I would much prefer if we didn't have to introduce
these.

>  };
>  #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)
>  
> @@ -380,6 +382,15 @@ static inline void i2c_unlock_adapter(struct i2c_adapter *adapter)
>  	rt_mutex_unlock(&adapter->bus_lock);
>  }
>  
> +/**
> + * i2c_trylock_adapter - Try to prevent access to an I2C bus segment
> + * @adapter: Target I2C bus segment
> + */
> +static inline int i2c_trylock_adapter(struct i2c_adapter *adapter)
> +{
> +	return rt_mutex_trylock(&adapter->bus_lock);
> +}
> +
>  /*flags for the client struct: */
>  #define I2C_CLIENT_PEC	0x04		/* Use Packet Error Checking */
>  #define I2C_CLIENT_TEN	0x10		/* we have a ten bit chip address */

Thanks,
-- 
Jean Delvare