i2c: Add generic I2C multiplexer using GPIO API
authorPeter Korsgaard <peter.korsgaard@barco.com>
Mon, 10 Jan 2011 21:11:23 +0000 (22:11 +0100)
committerJean Delvare <khali@endymion.delvare>
Mon, 10 Jan 2011 21:11:23 +0000 (22:11 +0100)
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>
Documentation/i2c/muxes/gpio-i2cmux [new file with mode: 0644]
MAINTAINERS
drivers/i2c/muxes/Kconfig
drivers/i2c/muxes/Makefile
drivers/i2c/muxes/gpio-i2cmux.c [new file with mode: 0644]
include/linux/gpio-i2cmux.h [new file with mode: 0644]

diff --git a/Documentation/i2c/muxes/gpio-i2cmux b/Documentation/i2c/muxes/gpio-i2cmux
new file mode 100644 (file)
index 0000000..811cd78
--- /dev/null
@@ -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,
+       },
+};
index 23d04363a1955503a817e9e53dae991e2ad43570..23a4765ab8d28d310c85a5895a660882600b8e93 100644 (file)
@@ -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/
index 4d91d80bfd23276804d8cb29ae5d1f130e06842a..90b7a01638998a5f9da8974429406f1f889e721f 100644 (file)
@@ -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
index d743806d9b42875dfb8832da002d31a5ec9ec6f4..4640436ea61f58f5562af3571899d9690eccbeb5 100644 (file)
@@ -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 (file)
index 0000000..7b6ce62
--- /dev/null
@@ -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 (file)
index 0000000..4a333bb
--- /dev/null
@@ -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 */