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>

3 files changed, 197 insertions, 0 deletions

diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index 4d91d80..90b7a01 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 d743806..4640436 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 0000000..7b6ce62
--- /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");