i2c: Multiplexed I2C bus core support

Add multiplexed bus core support. I2C driver for PCA954x I2C multiplexer series.

Signed-off-by Michael Lawnick <[email protected]>

Add multiplexed bus core support. I2C driver for PCA954x I2C multiplexer series.

Signed-off-by Michael Lawnick <[email protected]>

---
Based on kernel 2.6.33 +
[PATCH] i2c-core: Use per-adapter userspace device lists
by Jean Delware <[email protected]>
<http://article.gmane.org/gmane.linux.drivers.i2c/5994/>

 drivers/i2c/Kconfig         |    2 +
 drivers/i2c/Makefile        |    2 +-
 drivers/i2c/muxes/Kconfig   |   17 +++
 drivers/i2c/muxes/Makefile  |    8 +
 drivers/i2c/muxes/pca954x.c |  302 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/i2c/pca954x.h |   47 +++++++
 6 files changed, 377 insertions(+), 1 deletions(-)
 create mode 100755 drivers/i2c/muxes/Kconfig
 create mode 100755 drivers/i2c/muxes/Makefile
 create mode 100755 drivers/i2c/muxes/pca954x.c
 create mode 100755 include/linux/i2c/pca954x.h

drivers/i2c/Kconfig +2 -0

index 2cd6d78..21b0ac0 100755
@@ -44,6 +44,8 @@ config I2C_MUX
 	  handle multiplexed I2C bus topologies, by presenting each
 	  multiplexed segment as a I2C adapter.
 
+source drivers/i2c/muxes/Kconfig
+
 config I2C_CHARDEV
 	tristate "I2C device interface"
 	help

drivers/i2c/Makefile +1 -1

index a488e8b..1769a16 100755
@@ -6,7 +6,7 @@ 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/
+obj-y				+= busses/ chips/ muxes/ algos/
 
 ifeq ($(CONFIG_I2C_DEBUG_CORE),y)
 EXTRA_CFLAGS += -DDEBUG

drivers/i2c/muxes/Kconfig new file +0 -0

new file mode 100755
index 0000000..ec22db0

drivers/i2c/muxes/Kconfig new file +11 -0

+
+config I2C_MUX_PCA954x
+	tristate "Philips PCA954x I2C Mux/switches"
+	help
+	  If you say yes here you get support for the Philips PCA954x
+	  I2C mux/switch devices.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called pca954x.
+
+endmenu

drivers/i2c/muxes/Makefile new file +0 -0

new file mode 100755
index 0000000..575c1ca

drivers/i2c/muxes/Makefile new file +2 -0

+EXTRA_CFLAGS += -DDEBUG
+endif

drivers/i2c/muxes/pca954x.c new file +54 -0

new file mode 100755
index 0000000..12b5eb7
@@ -0,0 +1,302 @@
+/*
+ * I2C multiplexer
+ *
+ * Copyright (c) 2008-2009 Rodolfo Giometti <[email protected]>
+ * Copyright (c) 2008-2009 Eurotech S.p.A. <[email protected]>
+ *
+ * This module supports the PCA954x series of I2C multiplexer/switch chips
+ * made by Philips Semiconductors.
+ * This includes the:
+ *	 PCA9540, PCA9542, PCA9543, PCA9544, PCA9545, PCA9546, PCA9547
+ *	 and PCA9548.
+ *
+ * These chips are all controlled via the I2C bus itself, and all have a
+ * single 8-bit register. The upstream "parent" bus fans out to two,
+ * four, or eight downstream busses or channels; which of these
+ * are selected is determined by the chip type and register contents. A
+ * mux can select only one sub-bus at a time; a switch can select any
+ * combination simultaneously.
+ *
+ * Based on:
+ *	pca954x.c from Kumar Gala <[email protected]>
+ * Copyright (C) 2006
+ *
+ * Based on:
+ *	pca954x.c from Ken Harrenstien
+ * Copyright (C) 2004 Google, Inc. (Ken Harrenstien)
+ *
+ * Based on:
+ *	i2c-virtual_cb.c from Brian Kuschak <bkuschak-/[email protected]>
+ * and
+ *	pca9540.c from Jean Delvare <[email protected]>.
+ *
+ * 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/module.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/device.h>
+#include <linux/i2c.h>
+#include <linux/i2c-mux.h>
+
+#include <linux/i2c/pca954x.h>
+
+#define PCA954X_MAX_NCHANS 8
+
+enum pca_type {
+	pca_9540,
+	pca_9542,
+	pca_9543,
+	pca_9544,
+	pca_9545,

drivers/i2c/muxes/pca954x.c new file +51 -0

+};
+
+struct chip_desc {
+	u8 nchans;
+	u8 enable;	/* used for muxes only */
+	enum muxtype {
+		pca954x_ismux = 0,
+		pca954x_isswi
+	} muxtype;
+};
+
+/* Provide specs for the PCA954x types we know about */
+static const struct chip_desc chips[] = {
+	[pca_9540] = {
+		.nchans = 2,
+		.enable = 0x4,
+		.muxtype = pca954x_ismux,
+	},
+	[pca_9543] = {
+		.nchans = 2,
+		.muxtype = pca954x_isswi,
+	},
+	[pca_9544] = {
+		.nchans = 4,
+		.enable = 0x4,
+		.muxtype = pca954x_ismux,
+	},
+	[pca_9545] = {
+		.nchans = 4,
+		.muxtype = pca954x_isswi,
+	},
+	[pca_9547] = {
+		.nchans = 8,
+		.enable = 0x8,
+		.muxtype = pca954x_ismux,
+	},
+	[pca_9548] = {
+		.nchans = 8,
+		.muxtype = pca954x_isswi,
+	},
+};
+
+static const struct i2c_device_id pca954x_id[] = {
+	{ "pca9540", pca_9540 },
+	{ "pca9542", pca_9540 },
+	{ "pca9543", pca_9543 },
+	{ "pca9544", pca_9544 },
+	{ "pca9545", pca_9545 },
+	{ "pca9546", pca_9545 },
+	{ "pca9547", pca_9547 },
+	{ "pca9548", pca_9548 },

drivers/i2c/muxes/pca954x.c new file +89 -0

+		msg.len = 1;
+		buf[0] = val;
+		msg.buf = buf;
+		ret = adap->algo->master_xfer(adap, &msg, 1);
+	} else {
+		union i2c_smbus_data data;
+		ret = adap->algo->smbus_xfer(adap, client->addr,
+					     client->flags,
+					     I2C_SMBUS_WRITE,
+					     val, I2C_SMBUS_BYTE, &data);
+	}
+
+	return ret;
+}
+
+static int pca954x_select_chan(struct i2c_adapter *adap,
+			       void *client, u32 chan)
+{
+	struct pca954x *data = i2c_get_clientdata(client);
+	const struct chip_desc *chip = &chips[data->type];
+	u8 regval;
+	int ret = 0;
+
+	/* we make switches look like muxes, not sure how to be smarter */
+	if (chip->muxtype == pca954x_ismux)
+		regval = chan | chip->enable;
+	else
+		regval = 1 << chan;
+
+	/* Only select the channel if its different from the last channel */
+	if (data->last_chan != chan) {
+		ret = pca954x_reg_write(adap, client, regval);
+		data->last_chan = chan;
+	}
+
+	return ret;
+}
+
+static int pca954x_deselect_mux(struct i2c_adapter *adap,
+				void *client, u32 chan)
+{
+	struct pca954x *data = i2c_get_clientdata(client);
+
+	/* Deselect active channel */
+	data->last_chan = 0;
+	return pca954x_reg_write(adap, client, data->last_chan);
+}
+
+/*
+ * I2C init/probing/exit functions
+ */
+static int __devinit pca954x_probe(struct i2c_client *client,
+				   const struct i2c_device_id *id)
+{
+	struct i2c_adapter *adap = to_i2c_adapter(client->dev.parent);
+	struct pca954x_platform_data *pdata = client->dev.platform_data;
+	int num, force;
+	struct pca954x *data;
+	int ret = -ENODEV;
+
+	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE))
+		goto err;
+
+	data = kzalloc(sizeof(struct pca954x), GFP_KERNEL);
+	if (!data) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	i2c_set_clientdata(client, data);
+
+	/* Read the mux register at addr to verify
+	 * that the mux is in fact present.
+	 */
+	if (i2c_smbus_read_byte(client) < 0) {
+		dev_warn(&client->dev, "probe failed\n");
+		goto exit_free;
+	}
+
+	data->type = id->driver_data;
+	data->last_chan = 0;		   /* force the first selection */
+
+	/* Now create an adapter for each channel */
+	for (num = 0; num < chips[data->type].nchans; num++) {
+		force = 0;			  /* dynamic adap number */
+		if (pdata) {
+			if (num < pdata->num_modes)
+				/* force static number */
+				force = pdata->modes[num].adap_id;

drivers/i2c/muxes/pca954x.c new file +65 -0

+				force);
+			goto virt_reg_failed;
+		}
+	}
+
+	dev_info(&client->dev,
+		 "registered %d multiplexed busses for I2C %s %s\n",
+		 num, chips[data->type].muxtype == pca954x_ismux
+				? "mux" : "switch", client->name);
+
+	return 0;
+
+virt_reg_failed:
+	for (num--; num >= 0; num--)
+		i2c_del_mux_adapter(data->virt_adaps[num]);
+exit_free:
+	kfree(data);
+err:
+	return ret;
+}
+
+static int __devexit pca954x_remove(struct i2c_client *client)
+{
+	struct pca954x *data = i2c_get_clientdata(client);
+	const struct chip_desc *chip = &chips[data->type];
+	int i, err;
+
+	for (i = 0; i < chip->nchans; ++i)
+		if (data->virt_adaps[i]) {
+			err = i2c_del_mux_adapter(data->virt_adaps[i]);
+			if (err)
+				return err;
+			data->virt_adaps[i] = NULL;
+		}
+
+	kfree(data);
+	return 0;
+}
+
+static struct i2c_driver pca954x_driver = {
+	.driver		= {
+		.name	= "pca954x",
+		.owner	= THIS_MODULE,
+	},
+	.probe		= pca954x_probe,
+	.remove		= __devexit_p(pca954x_remove),
+	.id_table	= pca954x_id,
+};
+
+static int __init pca954x_init(void)
+{
+	return i2c_add_driver(&pca954x_driver);
+}
+
+static void __exit pca954x_exit(void)
+{
+	i2c_del_driver(&pca954x_driver);
+}
+
+module_init(pca954x_init);
+module_exit(pca954x_exit);
+
+MODULE_AUTHOR("Rodolfo Giometti <[email protected]>");
+MODULE_DESCRIPTION("PCA954x I2C mux/switch driver");
+MODULE_LICENSE("GPL v2");

include/linux/i2c/pca954x.h new file +15 -0

new file mode 100755
index 0000000..8032269
@@ -0,0 +1,47 @@
+/*
+ *
+ * pca954x.h - I2C multiplexer/switch support
+ *
+ * Copyright (c) 2008-2009 Rodolfo Giometti <[email protected]>
+ * Copyright (c) 2008-2009 Eurotech S.p.A. <[email protected]>
+ * Michael Lawnick <[email protected]>
+ *
+ * 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

include/linux/i2c/pca954x.h new file +9 -0

+#define _I2C_PCA954X_H
+
+/* Platform data for the PCA954x I2C multiplexers */
+
+/* Per channel initialisation data:
+ * @adap_id: bus number for the adapter. 0 = don't care
+ * @deselect_on_exit: set this entry to 1, if your H/W needs deselection
+ *                    of this channel after transaction.
+ *

Hi Michael,

Quoted 4 lines · Michael Lawnick

Add multiplexed bus core support. I2C driver for PCA954x I2C multiplexer series.

Signed-off-by Michael Lawnick <[email protected]>

Review:

I've fixed all these small issues myself; no need to resend. Thanks (to you and Rodolfo as well) for your contribution!

drivers/i2c/muxes/pca954x.c new file +6 -0

+static int pca954x_select_chan(struct i2c_adapter *adap,
+			       void *client, u32 chan)
+{
+	struct pca954x *data = i2c_get_clientdata(client);
+	const struct chip_desc *chip = &chips[data->type];
+	u8 regval;

drivers/i2c/muxes/pca954x.c new file +6 -0

+		ret = pca954x_reg_write(adap, client, regval);
+		data->last_chan = chan;
+	}
+
+	return ret;
+}

Hi Michael,

I just hit a bug...

Quoted 6 lines · Michael Lawnick

drivers/i2c/muxes/pca954x.c new file +6 -0

+static int pca954x_select_chan(struct i2c_adapter *adap,
+			       void *client, u32 chan)
+{
+	struct pca954x *data = i2c_get_clientdata(client);
+	const struct chip_desc *chip = &chips[data->type];
+	u8 regval;

drivers/i2c/muxes/pca954x.c line 163

Quoted 10 lines

drivers/i2c/muxes/pca954x.c new file +10 -0

+	int ret = 0;
+
+	/* we make switches look like muxes, not sure how to be smarter */
+	if (chip->muxtype == pca954x_ismux)
+		regval = chan | chip->enable;
+	else
+		regval = 1 << chan;
+
+	/* Only select the channel if its different from the last channel */
+	if (data->last_chan != chan) {

That's not right. data->last_chan is 0 after initialization or deselection, but selecting channel 0 is valid and must be possible.

So you either want to use a different initialization value (e.g. 0xff) or store the register value in data->last_chan instead of the channel number. I went for the latter.

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

Signed-off-by Michael Lawnick <[email protected]>

Add multiplexed bus core support.

Michael Lawnick said the following:

Quoted 1 line

Add multiplexed bus core support.

...

Ping

Jean, still any chance to get that done into .35?

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

Signed-off-by Michael Lawnick <[email protected]>

---
Based on kernel 2.6.33 +
[PATCH] i2c-core: Use per-adapter userspace device lists
by Jean Delware <[email protected]>
<http://article.gmane.org/gmane.linux.drivers.i2c/5994/>

 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

drivers/i2c/Kconfig +0 -0

index 8d8a00e..2cd6d78 100755

drivers/i2c/Kconfig +0 -0

 config I2C_CHARDEV
 	tristate "I2C device interface"
 	help

drivers/i2c/Makefile +1 -0

index ba26e6c..a488e8b 100755
@@ -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)

drivers/i2c/i2c-core.c +0 -0

index fc93e28..682966a 100755

drivers/i2c/i2c-core.c +13 -0

 #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);

drivers/i2c/i2c-core.c +4 -0

+	}
+	return result;
+}
+
 static int i2c_check_addr(struct i2c_adapter *adapter, int addr)
 {

drivers/i2c/i2c-core.c +33 -4

+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;

drivers/i2c/i2c-dev.c +7 -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);

drivers/i2c/i2c-dev.c +12 -1

+	}
+	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,

drivers/i2c/i2c-mux.c new file +11 -0

new file mode 100755
index 0000000..f88d29a
@@ -0,0 +1,184 @@
+/*
+ * Multiplexed I2C bus driver.
+ *
+ * Copyright (c) 2008-2009 Rodolfo Giometti <[email protected]>
+ * Copyright (c) 2008-2009 Eurotech S.p.A. <[email protected]>
+ *
+ * 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:

drivers/i2c/i2c-mux.c new file +8 -0

+
+#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 */

drivers/i2c/i2c-mux.c new file +10 -0

+
+	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;
+}
+

drivers/i2c/i2c-mux.c new file +31 -0

+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.

drivers/i2c/i2c-mux.c new file +10 -0

+	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 {

drivers/i2c/i2c-mux.c new file +13 -0

+
+	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 <[email protected]>");
+MODULE_DESCRIPTION("I2C driver for multiplexed I2C busses");
+MODULE_LICENSE("GPL v2");

include/linux/i2c-mux.h new file +36 -0

new file mode 100755
index 0000000..0d5d6c8
@@ -0,0 +1,46 @@
+/*
+ *
+ * i2c-mux.h - functions for the i2c-bus mux support
+ *
+ * Copyright (c) 2008-2009 Rodolfo Giometti <[email protected]>
+ * Copyright (c) 2008-2009 Eurotech S.p.A. <[email protected]>
+ * Michael Lawnick <[email protected]>
+ *
+ * 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,

include/linux/i2c.h +2 -0

 };
 #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

Hi Michael,

drivers/i2c/i2c-mux.c line 145

Quoted 1 line

drivers/i2c/i2c-mux.c new file +1 -0

+	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.

Jean Delvare said the following:

Quoted 9 lines

Hi Michael,

drivers/i2c/i2c-mux.c line 145

Quoted 1 line

drivers/i2c/i2c-mux.c new file +1 -0

+	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.

Quoted 3 lines

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

this is a core part of mux management. You need it for checking whether the current client that is to be added is already present. The problem is to efficiently parse down a mux tree towards the leaves. Sub-muxes are registered as i2c clients to their upper bus.

I found no way to separate muxes from normal clients.

So there were two ideas:
invent a client-type field in i2c-client or to hold a separate list. The first one e.g. would have the possibility to provide basic info in sysFs but I feared a general debate. So I decided to go the other way which is hidden to the outer world.

If you don't like this way, I'd need some ideas how to do it.

Quoted 1 line

Hi Michael,

Quoted 5 lines

I would walk the device tree maintained by the driver core (using device_for_each_child) and filtering out irrelevant devices. Basically filtering on dev->type == &i2c_adapter_type should do the trick, methinks.

Quoted 7 lines

drivers/i2c/i2c-core.c +1 -1

 	if (adapter->algo->smbus_xfer) {
-		rt_mutex_lock(&adapter->bus_lock);
+		i2c_mux_tree_lock(adapter);
 
 		/* Retry automatically on arbitration loss */
 		orig_jiffies = jiffies;

drivers/i2c/i2c-core.c s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags, · line 1956

Quoted 8 lines

drivers/i2c/i2c-core.c +1 -1

@@ -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.

Quoted 9 lines

drivers/i2c/i2c-dev.c +0 -0

index f4110aa..da5327f 100755
@@ -193,12 +193,56 @@ static int i2cdev_check(struct device *dev, void *addrp)
 	return dev->driver ? -EBUSY : 0;
 }
 

drivers/i2c/i2c-dev.c static int i2cdev_check(struct device *dev, void *addrp) · line 200

Quoted 5 lines

drivers/i2c/i2c-dev.c +5 -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 :(

Hi Jean,

Jean Delvare said the following:
...

Quoted 21 lines

Quoted 7 lines

drivers/i2c/i2c-core.c +1 -1

 	if (adapter->algo->smbus_xfer) {
-		rt_mutex_lock(&adapter->bus_lock);
+		i2c_mux_tree_lock(adapter);
 
 		/* Retry automatically on arbitration loss */
 		orig_jiffies = jiffies;

drivers/i2c/i2c-core.c s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags, · line 1956

Quoted 8 lines

drivers/i2c/i2c-core.c +1 -1

@@ -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.

Quoted 2 lines

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.

Agree, but I'd vote to do it not inline as its now. Otherwise we start to export mux implementation details in i2c.h

Quoted 8 lines

Quoted 8 lines

drivers/i2c/i2c-dev.c +0 -0

index f4110aa..da5327f 100755
@@ -193,12 +193,56 @@ static int i2cdev_check(struct device *dev, void *addrp)
 	return dev->driver ? -EBUSY : 0;
 }
 

Quoted 9 lines

drivers/i2c/i2c-dev.c static int i2cdev_check(struct device *dev, void *addrp) · line 200

Quoted 5 lines

drivers/i2c/i2c-dev.c +5 -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 :(

Must this and the above be done in an extra patch or can it be mixed into this mux patch?