[PATCH] i2c: add generic I2C multiplexer using gpio api

[PATCH] i2c: add generic I2C multiplexer using gpio api

[Peter Korsgaard]

Add an i2c bus driver providing virtual i2c busses using a hardware MUX
sitting on a master bus and controlled through gpio pins.

E.G. something like:

  ----------              ----------  Virtual bus 1   - - - - -
 |          | SCL/SDA    |          |-------------- |           |
 |          |------------|          |
 |          |            |          | Virtual bus 2 |           |
 |  Linux   | GPIO 1..N  |   MUX    |---------------   Devices
 |          |------------|          |               |           |
 |          |            |          | Virtual bus M
 |          |            |          |---------------|           |
  ----------              ----------                  - - - - -

SCL/SDA of the master I2C bus is multiplexed to virtual bus 1..M
according to the settings of the GPIO pins 1..N.

Signed-off-by: Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@public.gmane.org>
---
 Documentation/i2c/busses/i2c-gpiomux |   65 +++++++++++
 MAINTAINERS                          |    7 ++
 drivers/i2c/busses/Kconfig           |   12 ++
 drivers/i2c/busses/Makefile          |    1 +
 drivers/i2c/busses/i2c-gpiomux.c     |  196 ++++++++++++++++++++++++++++++++++
 include/linux/i2c-gpiomux.h          |   35 ++++++
 6 files changed, 316 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/i2c/busses/i2c-gpiomux
 create mode 100644 drivers/i2c/busses/i2c-gpiomux.c
 create mode 100644 include/linux/i2c-gpiomux.h

diff --git a/Documentation/i2c/busses/i2c-gpiomux b/Documentation/i2c/busses/i2c-gpiomux
new file mode 100644
index 0000000..b0a7746
--- /dev/null
+++ b/Documentation/i2c/busses/i2c-gpiomux
@@ -0,0 +1,65 @@
+Kernel driver i2c-gpiomux
+
+Author: Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@public.gmane.org>
+
+Description
+-----------
+
+i2c-gpiomux is an i2c bus driver providing virtual I2C busses from a
+master I2C bus and a hardware MUX controlled through GPIO pins.
+
+E.G.:
+
+  ----------              ----------  Virtual bus 1   - - - - -
+ |          | SCL/SDA    |          |-------------- |           |
+ |          |------------|          |
+ |          |            |          | Virtual bus 2 |           |
+ |  Linux   | GPIO 1..N  |   MUX    |---------------   Devices
+ |          |------------|          |               |           |
+ |          |            |          | Virtual bus M
+ |          |            |          |---------------|           |
+  ----------              ----------                  - - - - -
+
+SCL/SDA of the master I2C bus is multiplexed to virtual bus 1..M
+according to the settings of the GPIO pins 1..N.
+
+Usage
+-----
+
+i2c-gpiomux uses the platform bus, so you need to provide a struct
+platform_device with the platform_data pointing to a struct
+gpiomux_i2c_platform_data with the I2C adapter number of the master
+bus, the number of virtual busses to create and the GPIO pins used
+to control it. See include/linux/i2c-gpiomux.h for details.
+
+E.G. something like this for a MUX providing 4 virtual busses
+controlled through 3 GPIO pins:
+
+#include <linux/i2c-gpiomux.h>
+#include <linux/platform_device.h>
+
+static unsigned myboard_gpiomux_pins[] = {
+	AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC24
+};
+
+static unsigned myboard_gpiomux_values[] = {
+	0, 1, 2, 3
+};
+
+static struct gpiomux_i2c_platform_data myboard_i2cmux_data = {
+	.parent		= 1,
+	.base_nr	= 2,
+	.busses		= ARRAY_SIZE(myboard_gpiomux_values),
+	.gpios		= ARRAY_SIZE(myboard_gpiomux_pins),
+	.gpio		= myboard_gpiomux_pins,
+	.values		= myboard_gpiomux_values,
+	.idle		= 4,
+};
+
+static struct platform_device myboard_i2cmux = {
+	.name		= "i2c-gpiomux",
+	.id		= 0,
+	.dev		= {
+		.platform_data	= &myboard_i2cmux_data,
+	},
+};
diff --git a/MAINTAINERS b/MAINTAINERS
index 7642365..f80ad93 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2453,6 +2453,13 @@ S:	Supported
 F:	drivers/i2c/busses/i2c-gpio.c
 F:	include/linux/i2c-gpio.h
 
+GENERIC GPIO I2C MULTIPLEXER DRIVER
+M:	Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@public.gmane.org>
+L:	linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
+S:	Supported
+F:	drivers/i2c/busses/i2c-gpiomux.c
+F:	include/linux/i2c-gpiomux.h
+
 GENERIC HDLC (WAN) DRIVERS
 M:	Krzysztof Halasa <khc-9GfyWEdoJtJmR6Xm/wNWPw@public.gmane.org>
 W:	http://www.kernel.org/pub/linux/utils/net/hdlc/
diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index bceafbf..055b0f1 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -364,6 +364,18 @@ config I2C_GPIO
 	  This is a very simple bitbanging I2C driver utilizing the
 	  arch-neutral GPIO API to control the SCL and SDA lines.
 
+config I2C_GPIOMUX
+	tristate "GPIO-based I2C multiplexer"
+	depends on GENERIC_GPIO
+	help
+	  If you say yes to this option, support will be included for a
+	  GPIO based I2C multiplexer. This driver provides virtual I2C
+	  busses from a master bus through a MUX controlled through
+	  the generic GPIO interface.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called i2c-gpiomux.
+
 config I2C_HIGHLANDER
 	tristate "Highlander FPGA SMBus interface"
 	depends on SH_HIGHLANDER
diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
index 936880b..5ec15ec 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -35,6 +35,7 @@ obj-$(CONFIG_I2C_CPM)		+= i2c-cpm.o
 obj-$(CONFIG_I2C_DAVINCI)	+= i2c-davinci.o
 obj-$(CONFIG_I2C_DESIGNWARE)	+= i2c-designware.o
 obj-$(CONFIG_I2C_GPIO)		+= i2c-gpio.o
+obj-$(CONFIG_I2C_GPIOMUX)	+= i2c-gpiomux.o
 obj-$(CONFIG_I2C_HIGHLANDER)	+= i2c-highlander.o
 obj-$(CONFIG_I2C_IBM_IIC)	+= i2c-ibm_iic.o
 obj-$(CONFIG_I2C_IMX)		+= i2c-imx.o
diff --git a/drivers/i2c/busses/i2c-gpiomux.c b/drivers/i2c/busses/i2c-gpiomux.c
new file mode 100644
index 0000000..b4cc9e2
--- /dev/null
+++ b/drivers/i2c/busses/i2c-gpiomux.c
@@ -0,0 +1,196 @@
+/*
+ * I2C multiplexer using GPIO API
+ *
+ * Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@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 version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/i2c.h>
+#include <linux/i2c-gpiomux.h>
+#include <linux/platform_device.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/gpio.h>
+
+struct gpiomux_i2c {
+	struct i2c_adapter *parent; /* parent bus */
+	struct i2c_adapter *adap; /* children busses */
+	struct gpiomux_i2c_platform_data data;
+};
+
+static void gpiomux_set(struct gpiomux_i2c *i2c, unsigned val)
+{
+	int i;
+
+	for (i = 0;  i < i2c->data.gpios; i++)
+		gpio_set_value(i2c->data.gpio[i], val & (1<<i));
+}
+
+static int gpiomux_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
+			 int num)
+{
+	struct gpiomux_i2c *i2c = i2c_get_adapdata(adap);
+	int nr = adap->nr - i2c->data.base_nr;
+	int ret;
+
+	rt_mutex_lock(&i2c->parent->bus_lock);
+
+	gpiomux_set(i2c, i2c->data.values[nr]);
+	ret = i2c->parent->algo->master_xfer(i2c->parent, msgs, num);
+	gpiomux_set(i2c, i2c->data.idle);
+
+	rt_mutex_unlock(&i2c->parent->bus_lock);
+
+	return ret;
+}
+
+static u32 gpiomux_func(struct i2c_adapter *adap)
+{
+	struct gpiomux_i2c *i2c = i2c_get_adapdata(adap);
+
+	return i2c->parent->algo->functionality(i2c->parent);
+}
+
+static struct i2c_algorithm gpiomux_algorithm = {
+	.master_xfer	= gpiomux_xfer,
+	.functionality	= gpiomux_func,
+};
+
+static struct i2c_adapter gpiomux_adapter = {
+	.owner		= THIS_MODULE,
+	.name		= "gpiomux",
+	.class		= I2C_CLASS_HWMON,
+	.algo		= &gpiomux_algorithm,
+	.timeout	= 2,
+	.retries	= 1
+};
+
+static int __devinit gpiomux_probe(struct platform_device *pdev)
+{
+	struct gpiomux_i2c *i2c;
+	struct gpiomux_i2c_platform_data *pdata;
+	struct i2c_adapter *adap;
+	int i, j, ret;
+
+	pdata = pdev->dev.platform_data;
+	if (!pdata) {
+		dev_err(&pdev->dev, "Missing platform data\n");
+		return -ENODEV;
+	}
+
+	adap = i2c_get_adapter(pdata->parent);
+	if (!adap) {
+		dev_err(&pdev->dev, "Parent adapter (%d) not found\n",
+			pdata->parent);
+		return -ENODEV;
+	}
+
+	i2c = kzalloc(sizeof(*i2c), GFP_KERNEL);
+	if (!i2c) {
+		ret = -ENOMEM;
+		goto alloc_failed;
+	}
+
+	i2c->parent = adap;
+	i2c->data = *pdata;
+	i2c->adap = kzalloc(sizeof(struct i2c_adapter)*pdata->busses,
+			    GFP_KERNEL);
+	if (!i2c->adap) {
+		ret = -ENOMEM;
+		goto alloc_failed2;
+	}
+
+	for (i = 0; i < pdata->gpios; i++) {
+		ret = gpio_request(pdata->gpio[i], "i2c-gpiomux");
+		if (ret)
+			goto err_request_gpio;
+		gpio_direction_output(pdata->gpio[i], pdata->idle & (1<<i));
+	}
+
+	for (i = 0; i < pdata->busses; i++) {
+		i2c->adap[i] = gpiomux_adapter;
+		i2c->adap[i].dev.parent = &adap->dev;
+		i2c->adap[i].nr = pdata->base_nr + i;
+
+		snprintf(i2c->adap[i].name, I2C_NAME_SIZE, "%s.%d",
+			 gpiomux_adapter.name, i);
+		i2c_set_adapdata(&i2c->adap[i], i2c);
+		ret = i2c_add_numbered_adapter(&i2c->adap[i]);
+		if (ret) {
+			dev_err(&pdev->dev, "Failed to add adapter %d\n", i);
+			goto add_adapter_failed;
+		}
+	}
+
+	dev_info(&pdev->dev, "%d port mux on %s adapter\n",
+		 pdata->busses, adap->name);
+
+	platform_set_drvdata(pdev, i2c);
+
+	return 0;
+
+ add_adapter_failed:
+	for (j = 0; j < i; j++)
+		i2c_del_adapter(&i2c->adap[j]);
+	i = pdata->gpios;
+ err_request_gpio:
+	for (j = 0; j < i; j++)
+		gpio_free(pdata->gpio[j]);
+	kfree(i2c->adap);
+ alloc_failed2:
+	kfree(i2c);
+ alloc_failed:
+	i2c_put_adapter(adap);
+
+	return ret;
+}
+
+static int __devexit gpiomux_remove(struct platform_device *pdev)
+{
+	struct gpiomux_i2c *i2c = platform_get_drvdata(pdev);
+	int i;
+
+	for (i = 0; i < i2c->data.busses; i++)
+		i2c_del_adapter(&i2c->adap[i]);
+
+	for (i = 0; i < i2c->data.gpios; i++)
+		gpio_free(i2c->data.gpio[i]);
+
+	platform_set_drvdata(pdev, NULL);
+	i2c_put_adapter(i2c->parent);
+	kfree(i2c->adap);
+	kfree(i2c);
+
+	return 0;
+}
+
+static struct platform_driver gpiomux_driver = {
+	.probe  = gpiomux_probe,
+	.remove = __devexit_p(gpiomux_remove),
+	.driver = {
+		.owner = THIS_MODULE,
+		.name = "i2c-gpiomux",
+	},
+};
+
+static int __init gpiomux_init(void)
+{
+	return platform_driver_register(&gpiomux_driver);
+}
+
+static void __exit gpiomux_exit(void)
+{
+	platform_driver_unregister(&gpiomux_driver);
+}
+
+module_init(gpiomux_init);
+module_exit(gpiomux_exit);
+
+MODULE_DESCRIPTION("GPIO-based I2C multiplexer driver");
+MODULE_AUTHOR("Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@public.gmane.org>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:i2c-gpiomux");
diff --git a/include/linux/i2c-gpiomux.h b/include/linux/i2c-gpiomux.h
new file mode 100644
index 0000000..2388ff2
--- /dev/null
+++ b/include/linux/i2c-gpiomux.h
@@ -0,0 +1,35 @@
+/*
+ * i2c-gpiomux interface to platform code
+ *
+ * Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@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 version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef _LINUX_I2C_GPIOMUX_H
+#define _LINUX_I2C_GPIOMUX_H
+
+/**
+ * struct gpiomux_i2c_platform_data - Platform-dependent data for i2c-gpiomux
+ * @parent: Parent I2C bus adapter number
+ * @base_nr: Base bus number value to number adapters from
+ * @busses: Number of multiplexer positions (busses to instantiate)
+ * @gpios: Number of gpios used to control MUX
+ * @gpio: Array of @gpios gpio numbers used to control MUX
+ * @values: Array of @bussed bitmasks of gpio settings (low/high) for each
+ *	position
+ * @idle: Bitmask to write to MUX when idle
+ */
+struct gpiomux_i2c_platform_data {
+	int parent;
+	int base_nr;
+	int busses;
+	int gpios;
+	unsigned *gpio;
+	unsigned *values;
+	unsigned idle;
+};
+
+#endif /* _LINUX_I2C_GPIOMUX_H */
-- 
1.7.1

Re: [PATCH] i2c: add generic I2C multiplexer using gpio api

[Peter Korsgaard]

>>>>> "Peter" == Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@public.gmane.org> writes:

 Peter> Add an i2c bus driver providing virtual i2c busses using a hardware
 Peter> MUX sitting on a master bus and controlled through gpio pins.

 Peter> E.G. something like:

 Peter>   ----------              ----------  Virtual bus 1   - - - - -
 Peter>  |          | SCL/SDA    |          |-------------- |           |
 Peter>  |          |------------|          |
 Peter>  |          |            |          | Virtual bus 2 |           |
 Peter>  |  Linux   | GPIO 1..N  |   MUX    |---------------   Devices
 Peter>  |          |------------|          |               |           |
 Peter>  |          |            |          | Virtual bus M
 Peter>  |          |            |          |---------------|           |
 Peter>   ----------              ----------                  - - - - -

 Peter> SCL/SDA of the master I2C bus is multiplexed to virtual bus 1..M
 Peter> according to the settings of the GPIO pins 1..N.

 Peter> Signed-off-by: Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@public.gmane.org>

Comments?

-- 
Bye, Peter Korsgaard

Re: [PATCH] i2c: add generic I2C multiplexer using gpio api

[Jean Delvare]

On Tue, 20 Jul 2010 11:13:48 +0200, Peter Korsgaard wrote:
> >>>>> "Peter" == Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@public.gmane.org> writes:
> 
>  Peter> Add an i2c bus driver providing virtual i2c busses using a hardware
>  Peter> MUX sitting on a master bus and controlled through gpio pins.
> 
>  Peter> E.G. something like:
> 
>  Peter>   ----------              ----------  Virtual bus 1   - - - - -
>  Peter>  |          | SCL/SDA    |          |-------------- |           |
>  Peter>  |          |------------|          |
>  Peter>  |          |            |          | Virtual bus 2 |           |
>  Peter>  |  Linux   | GPIO 1..N  |   MUX    |---------------   Devices
>  Peter>  |          |------------|          |               |           |
>  Peter>  |          |            |          | Virtual bus M
>  Peter>  |          |            |          |---------------|           |
>  Peter>   ----------              ----------                  - - - - -
> 
>  Peter> SCL/SDA of the master I2C bus is multiplexed to virtual bus 1..M
>  Peter> according to the settings of the GPIO pins 1..N.
> 
>  Peter> Signed-off-by: Peter Korsgaard <peter.korsgaard-ob4gmnvZ1/cAvxtiuMwx3w@public.gmane.org>
> 
> Comments?

Michael and myself are in the process of adding core support for bus
multiplexing to the i2c subsystem. There is no point in reviewing more
specific implementations until the core part is merged (which is
scheduled to happen in kernel 2.6.36.)

-- 
Jean Delvare

Re: [PATCH] i2c: add generic I2C multiplexer using gpio api

[Peter Korsgaard]

>>>>> "Jean" == Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org> writes:

Hi,

 Jean> Michael and myself are in the process of adding core support for
 Jean> bus multiplexing to the i2c subsystem. There is no point in
 Jean> reviewing more specific implementations until the core part is
 Jean> merged (which is scheduled to happen in kernel 2.6.36.)

But this patch is independent from that work as the mux access isn't
through I2C, hence no changes to i2c-core needed.

Do you want me to resend or do you still have the original patch?

-- 
Bye, Peter Korsgaard

Re: [PATCH] i2c: add generic I2C multiplexer using gpio api

[Jean Delvare]

On Tue, 20 Jul 2010 11:58:09 +0200, Peter Korsgaard wrote:
> >>>>> "Jean" == Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org> writes:
> 
> Hi,
> 
>  Jean> Michael and myself are in the process of adding core support for
>  Jean> bus multiplexing to the i2c subsystem. There is no point in
>  Jean> reviewing more specific implementations until the core part is
>  Jean> merged (which is scheduled to happen in kernel 2.6.36.)
> 
> But this patch is independent from that work as the mux access isn't
> through I2C, hence no changes to i2c-core needed.

The problem is exactly that your patch is independent. It _should_
build on top of Michael's work, to avoid redundancy.

> Do you want me to resend or do you still have the original patch?

I have it, but I don't intend to look at it. First I get Michael's work
upstream, and then I wait for you to submit a new patch taking benefit
of it.

-- 
Jean Delvare

Re: [PATCH] i2c: add generic I2C multiplexer using gpio api

[Michael Lawnick]

Peter Korsgaard said the following:
>>>>>> "Jean" == Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org> writes:
> 
> Hi,
> 
>  Jean> Michael and myself are in the process of adding core support for
>  Jean> bus multiplexing to the i2c subsystem. There is no point in
>  Jean> reviewing more specific implementations until the core part is
>  Jean> merged (which is scheduled to happen in kernel 2.6.36.)
> 
> But this patch is independent from that work as the mux access isn't
> through I2C, hence no changes to i2c-core needed.

i2c-mux patch does not expect path control via i2c.
Your scenario fits perfectly.

-- 
KR
Michael Lawnick

Re: [PATCH] i2c: add generic I2C multiplexer using gpio api

[Peter Korsgaard]

>>>>> "Jean" == Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org> writes:

 Jean> The problem is exactly that your patch is independent. It _should_
 Jean> build on top of Michael's work, to avoid redundancy.

Why? We've discussed this for years, E.G.:

http://www.mail-archive.com/i2c-GZX6beZjE8VD60Wz+7aTrA@public.gmane.org/msg01539.html

None of the locking changes in core are needed when the MUX isn't
controlled through I2C. I guess I could use the i2c-mux.c functions, as
there's some overlap in the trivial gpiomux_xfer/gpiomux_func functions,
but that can easily be done once the mux stuff is merged.

-- 
Bye, Peter Korsgaard

Re: [PATCH] i2c: add generic I2C multiplexer using gpio api

[Peter Korsgaard]

>>>>> "Michael" == Michael Lawnick <ml.lawnick-Mmb7MZpHnFY@public.gmane.org> writes:

 >> But this patch is independent from that work as the mux access isn't
 >> through I2C, hence no changes to i2c-core needed.

 Michael> i2c-mux patch does not expect path control via i2c.
 Michael> Your scenario fits perfectly.

Hmm, I'll take a closer look at the last version then - sorry. In the
past it afaik did. What is the point of the i2c-core changes if path
control isn't via i2c?

-- 
Bye, Peter Korsgaard

Re: [PATCH] i2c: add generic I2C multiplexer using gpio api

[Michael Lawnick]

Peter Korsgaard said the following:
>>>>>> "Michael" == Michael Lawnick <ml.lawnick-Mmb7MZpHnFY@public.gmane.org> writes:
> 
>  >> But this patch is independent from that work as the mux access isn't
>  >> through I2C, hence no changes to i2c-core needed.
> 
>  Michael> i2c-mux patch does not expect path control via i2c.
>  Michael> Your scenario fits perfectly.
> 
> Hmm, I'll take a closer look at the last version then - sorry. In the
> past it afaik did. What is the point of the i2c-core changes if path
> control isn't via i2c?
> 
The changes in i2c-core are mostly for traversing the tree and check for
duplicate addresses.
>From i2c-core and user space view there is no logical difference between
a h/w adapter and a multiplexer. They are all handled the same.
But I fear your question arises from your different approach. May be it
gets more clear after looking into i2c-mux.c and pca954x.c.

-- 
KR
Michael Lawnick