i2c: Add generic I2C multiplexer using GPIO API

Add an i2c mux driver providing access to i2c bus segments using a
hardware MUX sitting on a master bus and controlled through gpio pins.

E.G. something like:

  ----------              ----------  Bus segment 1   - - - - -
 |          | SCL/SDA    |          |-------------- |           |
 |          |------------|          |
 |          |            |          | Bus segment 2 |           |
 |  Linux   | GPIO 1..N  |   MUX    |---------------   Devices
 |          |------------|          |               |           |
 |          |            |          | Bus segment M
 |          |            |          |---------------|           |
  ----------              ----------                  - - - - -

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

Signed-off-by: Peter Korsgaard <peter.korsgaard@barco.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

6 files changed, 308 insertions, 0 deletions

diff --git a/Documentation/i2c/muxes/gpio-i2cmux b/Documentation/i2c/muxes/gpio-i2cmux
new file mode 100644
index 000000000000..811cd78d4cdc
--- /dev/null
+++ b/Documentation/i2c/muxes/gpio-i2cmux
@@ -0,0 +1,65 @@
+Kernel driver gpio-i2cmux
+
+Author: Peter Korsgaard <peter.korsgaard@barco.com>
+
+Description
+-----------
+
+gpio-i2cmux is an i2c mux driver providing access to I2C bus segments
+from a master I2C bus and a hardware MUX controlled through GPIO pins.
+
+E.G.:
+
+  ----------              ----------  Bus segment 1   - - - - -
+ |          | SCL/SDA    |          |-------------- |           |
+ |          |------------|          |
+ |          |            |          | Bus segment 2 |           |
+ |  Linux   | GPIO 1..N  |   MUX    |---------------   Devices
+ |          |------------|          |               |           |
+ |          |            |          | Bus segment M
+ |          |            |          |---------------|           |
+  ----------              ----------                  - - - - -
+
+SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M
+according to the settings of the GPIO pins 1..N.
+
+Usage
+-----
+
+gpio-i2cmux uses the platform bus, so you need to provide a struct
+platform_device with the platform_data pointing to a struct
+gpio_i2cmux_platform_data with the I2C adapter number of the master
+bus, the number of bus segments to create and the GPIO pins used
+to control it. See include/linux/gpio-i2cmux.h for details.
+
+E.G. something like this for a MUX providing 4 bus segments
+controlled through 3 GPIO pins:
+
+#include <linux/gpio-i2cmux.h>
+#include <linux/platform_device.h>
+
+static const unsigned myboard_gpiomux_gpios[] = {
+        AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC24
+};
+
+static const unsigned myboard_gpiomux_values[] = {
+        0, 1, 2, 3
+};
+
+static struct gpio_i2cmux_platform_data myboard_i2cmux_data = {
+        .parent         = 1,
+        .base_nr        = 2, /* optional */
+        .values         = myboard_gpiomux_values,
+        .n_values       = ARRAY_SIZE(myboard_gpiomux_values),
+        .gpios          = myboard_gpiomux_gpios,
+        .n_gpios        = ARRAY_SIZE(myboard_gpiomux_gpios),
+        .idle           = 4, /* optional */
+};
+
+static struct platform_device myboard_i2cmux = {
+        .name           = "gpio-i2cmux",
+        .id             = 0,
+        .dev            = {
+                .platform_data  = &myboard_i2cmux_data,
+        },
+};
diff --git a/MAINTAINERS b/MAINTAINERS
index 23d04363a195..23a4765ab8d2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2608,6 +2608,14 @@ 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@barco.com>
+L:      linux-i2c@vger.kernel.org
+S:      Supported
+F:      drivers/i2c/muxes/gpio-i2cmux.c
+F:      include/linux/gpio-i2cmux.h
+F:      Documentation/i2c/muxes/gpio-i2cmux
+
 GENERIC HDLC (WAN) DRIVERS
 M:      Krzysztof Halasa <khc@pm.waw.pl>
 W:      http://www.kernel.org/pub/linux/utils/net/hdlc/
diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index 4d91d80bfd23..90b7a0163899 100644
--- a/drivers/i2c/muxes/Kconfig
+++ b/drivers/i2c/muxes/Kconfig
@@ -5,6 +5,18 @@
 menu "Multiplexer I2C Chip support"
         depends on I2C_MUX
 
+config I2C_MUX_GPIO
+        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 access to
+          I2C busses connected through a MUX, which is controlled
+          through GPIO pins.
+
+          This driver can also be built as a module.  If so, the module
+          will be called gpio-i2cmux.
+
 config I2C_MUX_PCA9541
         tristate "NXP PCA9541 I2C Master Selector"
         depends on EXPERIMENTAL
diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
index d743806d9b42..4640436ea61f 100644
--- a/drivers/i2c/muxes/Makefile
+++ b/drivers/i2c/muxes/Makefile
@@ -1,6 +1,7 @@
 #
 # Makefile for multiplexer I2C chip drivers.
 
+obj-$(CONFIG_I2C_MUX_GPIO)      += gpio-i2cmux.o
 obj-$(CONFIG_I2C_MUX_PCA9541)   += pca9541.o
 obj-$(CONFIG_I2C_MUX_PCA954x)   += pca954x.o
 
diff --git a/drivers/i2c/muxes/gpio-i2cmux.c b/drivers/i2c/muxes/gpio-i2cmux.c
new file mode 100644
index 000000000000..7b6ce624cd6e
--- /dev/null
+++ b/drivers/i2c/muxes/gpio-i2cmux.c
@@ -0,0 +1,184 @@
+/*
+ * I2C multiplexer using GPIO API
+ *
+ * Peter Korsgaard <peter.korsgaard@barco.com>
+ *
+ * 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-mux.h>
+#include <linux/gpio-i2cmux.h>
+#include <linux/platform_device.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/gpio.h>
+
+struct gpiomux {
+        struct i2c_adapter *parent;
+        struct i2c_adapter **adap; /* child busses */
+        struct gpio_i2cmux_platform_data data;
+};
+
+static void gpiomux_set(const struct gpiomux *mux, unsigned val)
+{
+        int i;
+
+        for (i = 0; i < mux->data.n_gpios; i++)
+                gpio_set_value(mux->data.gpios[i], val & (1 << i));
+}
+
+static int gpiomux_select(struct i2c_adapter *adap, void *data, u32 chan)
+{
+        struct gpiomux *mux = data;
+
+        gpiomux_set(mux, mux->data.values[chan]);
+
+        return 0;
+}
+
+static int gpiomux_deselect(struct i2c_adapter *adap, void *data, u32 chan)
+{
+        struct gpiomux *mux = data;
+
+        gpiomux_set(mux, mux->data.idle);
+
+        return 0;
+}
+
+static int __devinit gpiomux_probe(struct platform_device *pdev)
+{
+        struct gpiomux *mux;
+        struct gpio_i2cmux_platform_data *pdata;
+        struct i2c_adapter *parent;
+        int (*deselect) (struct i2c_adapter *, void *, u32);
+        unsigned initial_state;
+        int i, ret;
+
+        pdata = pdev->dev.platform_data;
+        if (!pdata) {
+                dev_err(&pdev->dev, "Missing platform data\n");
+                return -ENODEV;
+        }
+
+        parent = i2c_get_adapter(pdata->parent);
+        if (!parent) {
+                dev_err(&pdev->dev, "Parent adapter (%d) not found\n",
+                        pdata->parent);
+                return -ENODEV;
+        }
+
+        mux = kzalloc(sizeof(*mux), GFP_KERNEL);
+        if (!mux) {
+                ret = -ENOMEM;
+                goto alloc_failed;
+        }
+
+        mux->parent = parent;
+        mux->data = *pdata;
+        mux->adap = kzalloc(sizeof(struct i2c_adapter *) * pdata->n_values,
+                            GFP_KERNEL);
+        if (!mux->adap) {
+                ret = -ENOMEM;
+                goto alloc_failed2;
+        }
+
+        if (pdata->idle != GPIO_I2CMUX_NO_IDLE) {
+                initial_state = pdata->idle;
+                deselect = gpiomux_deselect;
+        } else {
+                initial_state = pdata->values[0];
+                deselect = NULL;
+        }
+
+        for (i = 0; i < pdata->n_gpios; i++) {
+                ret = gpio_request(pdata->gpios[i], "gpio-i2cmux");
+                if (ret)
+                        goto err_request_gpio;
+                gpio_direction_output(pdata->gpios[i],
+                                      initial_state & (1 << i));
+        }
+
+        for (i = 0; i < pdata->n_values; i++) {
+                u32 nr = pdata->base_nr ? (pdata->base_nr + i) : 0;
+
+                mux->adap[i] = i2c_add_mux_adapter(parent, mux, nr, i,
+                                                   gpiomux_select, deselect);
+                if (!mux->adap[i]) {
+                        ret = -ENODEV;
+                        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->n_values, parent->name);
+
+        platform_set_drvdata(pdev, mux);
+
+        return 0;
+
+add_adapter_failed:
+        for (; i > 0; i--)
+                i2c_del_mux_adapter(mux->adap[i - 1]);
+        i = pdata->n_gpios;
+err_request_gpio:
+        for (; i > 0; i--)
+                gpio_free(pdata->gpios[i - 1]);
+        kfree(mux->adap);
+alloc_failed2:
+        kfree(mux);
+alloc_failed:
+        i2c_put_adapter(parent);
+
+        return ret;
+}
+
+static int __devexit gpiomux_remove(struct platform_device *pdev)
+{
+        struct gpiomux *mux = platform_get_drvdata(pdev);
+        int i;
+
+        for (i = 0; i < mux->data.n_values; i++)
+                i2c_del_mux_adapter(mux->adap[i]);
+
+        for (i = 0; i < mux->data.n_gpios; i++)
+                gpio_free(mux->data.gpios[i]);
+
+        platform_set_drvdata(pdev, NULL);
+        i2c_put_adapter(mux->parent);
+        kfree(mux->adap);
+        kfree(mux);
+
+        return 0;
+}
+
+static struct platform_driver gpiomux_driver = {
+        .probe  = gpiomux_probe,
+        .remove = __devexit_p(gpiomux_remove),
+        .driver = {
+                .owner  = THIS_MODULE,
+                .name   = "gpio-i2cmux",
+        },
+};
+
+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@barco.com>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:gpio-i2cmux");
diff --git a/include/linux/gpio-i2cmux.h b/include/linux/gpio-i2cmux.h
new file mode 100644
index 000000000000..4a333bb0bd0d
--- /dev/null
+++ b/include/linux/gpio-i2cmux.h
@@ -0,0 +1,38 @@
+/*
+ * gpio-i2cmux interface to platform code
+ *
+ * Peter Korsgaard <peter.korsgaard@barco.com>
+ *
+ * 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_GPIO_I2CMUX_H
+#define _LINUX_GPIO_I2CMUX_H
+
+/* MUX has no specific idle mode */
+#define GPIO_I2CMUX_NO_IDLE     ((unsigned)-1)
+
+/**
+ * struct gpio_i2cmux_platform_data - Platform-dependent data for gpio-i2cmux
+ * @parent: Parent I2C bus adapter number
+ * @base_nr: Base I2C bus number to number adapters from or zero for dynamic
+ * @values: Array of bitmasks of GPIO settings (low/high) for each
+ *      position
+ * @n_values: Number of multiplexer positions (busses to instantiate)
+ * @gpios: Array of GPIO numbers used to control MUX
+ * @n_gpios: Number of GPIOs used to control MUX
+ * @idle: Bitmask to write to MUX when idle or GPIO_I2CMUX_NO_IDLE if not used
+ */
+struct gpio_i2cmux_platform_data {
+        int parent;
+        int base_nr;
+        const unsigned *values;
+        int n_values;
+        const unsigned *gpios;
+        int n_gpios;
+        unsigned idle;
+};
+
+#endif /* _LINUX_GPIO_I2CMUX_H */