i2c: Multiplexed I2C bus core support

Add multiplexed bus core support. I2C multiplexer and switches
like pca954x get instantiated as new adapters per port.

Signed-off-by: Michael Lawnick <[e-mail]>
Acked-by: Rodolfo Giometti <[e-mail]>
Signed-off-by: Jean Delvare <[e-mail]>

drivers/i2c/Kconfig

···
 	  This support is also available as a module.  If so, the module 
 	  will be called i2c-dev.
 
+config I2C_MUX
+	tristate "I2C bus multiplexing support"
+	depends on EXPERIMENTAL
+	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.
+
+	  This support is also available as a module.  If so, the module
+	  will be called i2c-mux.
+
 config I2C_HELPER_AUTO
 	bool "Autoselect pertinent helper modules"
 	default y

drivers/i2c/Makefile

···
 obj-$(CONFIG_I2C)		+= i2c-core.o
 obj-$(CONFIG_I2C_SMBUS)		+= i2c-smbus.o
 obj-$(CONFIG_I2C_CHARDEV)	+= i2c-dev.o
+obj-$(CONFIG_I2C_MUX)		+= i2c-mux.o
 obj-y				+= algos/ busses/
 
 ifeq ($(CONFIG_I2C_DEBUG_CORE),y)

drivers/i2c/i2c-core.c

···
 /* With some changes from Kyösti Mälkki <[e-mail]>.
    All SMBus-related things are written by Frodo Looijaard <[e-mail]>
    SMBus 2.0 support by Mark Studebaker <[e-mail]> and
-   Jean Delvare <[e-mail]> */
+   Jean Delvare <[e-mail]>
+   Mux support by Rodolfo Giometti <[e-mail]> and
+   Michael Lawnick <[e-mail]> */
 
 #include <linux/module.h>
 #include <linux/kernel.h>
···
 	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_busy);
+
+	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_children(struct device *dev, void *addrp)
+{
+	int result;
+
+	if (dev->type == &i2c_adapter_type)
+		result = device_for_each_child(dev, addrp,
+						i2c_check_mux_children);
+	else
+		result = __i2c_check_addr_busy(dev, addrp);
+
+	return result;
+}
+
 static int i2c_check_addr_busy(struct i2c_adapter *adapter, int addr)
 {
-	return device_for_each_child(&adapter->dev, &addr,
-				     __i2c_check_addr_busy);
+	int result = 0;
+
+	if (i2c_parent_is_i2c_adapter(adapter))
+		result = i2c_check_mux_parents(
+				    to_i2c_adapter(adapter->dev.parent), addr);
+
+	if (!result)
+		result = device_for_each_child(&adapter->dev, &addr,
+						i2c_check_mux_children);
+
+	return result;
 }
 
 /**
···
  */
 void i2c_lock_adapter(struct i2c_adapter *adapter)
 {
-	rt_mutex_lock(&adapter->bus_lock);
+	if (i2c_parent_is_i2c_adapter(adapter))
+		i2c_lock_adapter(to_i2c_adapter(adapter->dev.parent));
+	else
+		rt_mutex_lock(&adapter->bus_lock);
 }
 EXPORT_SYMBOL_GPL(i2c_lock_adapter);
 
···
  */
 static int i2c_trylock_adapter(struct i2c_adapter *adapter)
 {
-	return rt_mutex_trylock(&adapter->bus_lock);
+	if (i2c_parent_is_i2c_adapter(adapter))
+		return i2c_trylock_adapter(to_i2c_adapter(adapter->dev.parent));
+	else
+		return rt_mutex_trylock(&adapter->bus_lock);
 }
 
 /**
···
  */
 void i2c_unlock_adapter(struct i2c_adapter *adapter)
 {
-	rt_mutex_unlock(&adapter->bus_lock);
+	if (i2c_parent_is_i2c_adapter(adapter))
+		i2c_unlock_adapter(to_i2c_adapter(adapter->dev.parent));
+	else
+		rt_mutex_unlock(&adapter->bus_lock);
 }
 EXPORT_SYMBOL_GPL(i2c_unlock_adapter);
 
···
 	NULL
 };
 
-static struct device_type i2c_adapter_type = {
+struct device_type i2c_adapter_type = {
 	.groups		= i2c_adapter_attr_groups,
 	.release	= i2c_adapter_dev_release,
 };
+EXPORT_SYMBOL_GPL(i2c_adapter_type);
 
 #ifdef CONFIG_I2C_COMPAT
 static struct class_compat *i2c_adapter_compat_class;

drivers/i2c/i2c-dev.c

···
 	return dev->driver ? -EBUSY : 0;
 }
 
+/* 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 && i2c_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_children(struct device *dev, void *addrp)
+{
+	int result;
+
+	if (dev->type == &i2c_adapter_type)
+		result = device_for_each_child(dev, addrp,
+						i2cdev_check_mux_children);
+	else
+		result = i2cdev_check(dev, addrp);
+
+	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 = 0;
+
+	if (i2c_parent_is_i2c_adapter(adapter))
+		result = i2cdev_check_mux_parents(
+				    to_i2c_adapter(adapter->dev.parent), addr);
+
+	if (!result)
+		result = device_for_each_child(&adapter->dev, &addr,
+						i2cdev_check_mux_children);
+
+	return result;
 }
 
 static noinline int i2cdev_ioctl_rdrw(struct i2c_client *client,

drivers/i2c/i2c-mux.c

···
+/*
+ * Multiplexed I2C bus driver.
+ *
+ * Copyright (c) 2008-2009 Rodolfo Giometti <[e-mail]>
+ * Copyright (c) 2008-2009 Eurotech S.p.A. <[e-mail]>
+ * Copyright (c) 2009-2010 NSN GmbH & Co KG <[e-mail]>
+ *
+ * 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 <[e-mail]>
+ *	i2c-virtual.c from Ken Harrenstien, Copyright (c) 2004 Google, Inc.
+ *	i2c-virtual.c from Brian Kuschak <[e-mail]>
+ *
+ * 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/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 *, void *mux_dev, u32 chan_id);
+	int (*deselect)(struct i2c_adapter *, void *mux_dev, 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_adapter *parent = priv->parent;
+	int ret;
+
+	/* Switch to the right mux port and perform the transfer. */
+
+	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. */
+
+	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);
+	if (priv->deselect)
+		priv->deselect(parent, priv->mux_dev, 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->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);
+	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;
+	}
+
+	dev_info(&parent->dev, "Added multiplexed i2c bus %d\n",
+		 i2c_adapter_id(&priv->adap));
+
+	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;
+
+	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 <[e-mail]>");
+MODULE_DESCRIPTION("I2C driver for multiplexed I2C busses");
+MODULE_LICENSE("GPL v2");

include/linux/i2c-mux.h

···
+/*
+ *
+ * i2c-mux.h - functions for the i2c-bus mux support
+ *
+ * Copyright (c) 2008-2009 Rodolfo Giometti <[e-mail]>
+ * Copyright (c) 2008-2009 Eurotech S.p.A. <[e-mail]>
+ * Michael Lawnick <[e-mail]>
+ *
+ * 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 *,
+					       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_MUX_H */

include/linux/i2c.h

···
 #include <linux/of.h>		/* for struct device_node */
 
 extern struct bus_type i2c_bus_type;
+extern struct device_type i2c_adapter_type;
 
 /* --- General options ------------------------------------------------	*/
 
···
 static inline void i2c_set_adapdata(struct i2c_adapter *dev, void *data)
 {
 	dev_set_drvdata(&dev->dev, data);
+}
+
+static inline int i2c_parent_is_i2c_adapter(const struct i2c_adapter *adapter)
+{
+	return adapter->dev.parent != NULL
+		&& adapter->dev.parent->bus == &i2c_bus_type
+		&& adapter->dev.parent->type == &i2c_adapter_type;
 }
 
 /* Adapter locking functions, exported for shared pin cases */