[PATCH v3 0/7] mux controller abstraction and iio/i2c muxes

@@ -746,3 +746,58 @@ int iio_write_channel_raw(struct iio_channel *chan, int val)
 	return ret;
 }
 EXPORT_SYMBOL_GPL(iio_write_channel_raw);
+
+int iio_get_channel_ext_info_count(struct iio_channel *chan)
+{
+	const struct iio_chan_spec_ext_info *ext_info;
+	unsigned int i = 0;
+
+	if (!chan->channel->ext_info)
+		return i;
+
+	for (ext_info = chan->channel->ext_info; ext_info->name; ext_info++)
+		++i;
+
+	return i;
+}
+EXPORT_SYMBOL_GPL(iio_get_channel_ext_info_count);
+
+ssize_t iio_read_channel_ext_info(struct iio_channel *chan,
+				  const char *attr, char *buf)
+{
+	const struct iio_chan_spec_ext_info *ext_info;
+
+	if (!chan->channel->ext_info)
+		return -EINVAL;
+
+	for (ext_info = chan->channel->ext_info; ext_info->name; ++ext_info) {
+		if (strcmp(attr, ext_info->name))
+			continue;
+
+		return ext_info->read(chan->indio_dev, ext_info->private,
+				      chan->channel, buf);
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(iio_read_channel_ext_info);
+
+ssize_t iio_write_channel_ext_info(struct iio_channel *chan, const char *attr,
+				   const char *buf, size_t len)
+{
+	const struct iio_chan_spec_ext_info *ext_info;
+
+	if (!chan->channel->ext_info)
+		return -EINVAL;
+
+	for (ext_info = chan->channel->ext_info; ext_info->name; ++ext_info) {
+		if (strcmp(attr, ext_info->name))
+			continue;
+
+		return ext_info->write(chan->indio_dev, ext_info->private,
+				       chan->channel, buf, len);
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(iio_write_channel_ext_info);

@@ -271,4 +271,41 @@ int iio_read_channel_scale(struct iio_channel *chan, int *val,
 int iio_convert_raw_to_processed(struct iio_channel *chan, int raw,
 	int *processed, unsigned int scale);
 
+/**
+ * iio_get_channel_ext_info_count() - get number of ext_info attributes
+ *				      connected to the channel.
+ * @chan:		The channel being queried
+ *
+ * Returns the number of ext_info attributes
+ */
+int iio_get_channel_ext_info_count(struct iio_channel *chan);
+
+/**
+ * iio_read_channel_ext_info() - read ext_info attribute from a given channel
+ * @chan:		The channel being queried.
+ * @attr:		The ext_info attribute to read.
+ * @buf:		Where to store the attribute value. Assumed to hold
+ *			at least PAGE_SIZE bytes.
+ *
+ * Returns the number of bytes written to buf (perhaps w/o zero termination;
+ * it need not even be a string), or an error code.
+ */
+ssize_t iio_read_channel_ext_info(struct iio_channel *chan,
+				  const char *attr, char *buf);
+
+/**
+ * iio_write_channel_ext_info() - write ext_info attribute from a given channel
+ * @chan:		The channel being queried.
+ * @attr:		The ext_info attribute to read.
+ * @buf:		The new attribute value. Strings needs to be zero-
+ *			terminated, but the terminator should not be included
+ *			in the below len.
+ * @len:		The size of the new attribute value.
+ *
+ * Returns the number of accepted bytes, which should be the same as len.
+ * An error code can also be returned.
+ */
+ssize_t iio_write_channel_ext_info(struct iio_channel *chan, const char *attr,
+				   const char *buf, size_t len);
+
 #endif

@@ -330,7 +330,11 @@ MEM
   devm_kzalloc()
 
 MFD
- devm_mfd_add_devices()
+  devm_mfd_add_devices()
+
+MUX
+  devm_mux_control_get()
+  devm_mux_control_put()
 
 PCI
   pcim_enable_device()	: after success, all PCI ops become managed

@@ -8248,6 +8248,8 @@ MULTIPLEXER SUBSYSTEM
 M:	Peter Rosin <peda@axentia.se>
 S:	Maintained
 F:	Documentation/devicetree/bindings/misc/mux-*
+F:	include/linux/mux.h
+F:	drivers/misc/mux-*
 
 MULTISOUND SOUND DRIVER
 M:	Andrew Veliath <andrewtv@usa.net>

@@ -766,6 +766,29 @@ config PANEL_BOOT_MESSAGE
 	  An empty message will only clear the display at driver init time. Any other
 	  printf()-formatted message is valid with newline and escape codes.
 
+config MULTIPLEXER
+	tristate "Multiplexer subsystem"
+	help
+	  Multiplexer controller subsystem. Multiplexers are used in a
+	  variety of settings, and this subsystem abstracts their use
+	  so that the rest of the kernel sees a common interface. When
+	  multiple parallel multiplexers are controlled by one single
+	  multiplexer controller, this subsystem also coordinates the
+	  multiplexer accesses.
+
+if MULTIPLEXER
+
+config MUX_GPIO
+	tristate "GPIO-controlled MUX controller"
+	depends on OF && GPIOLIB
+	help
+	  GPIO-controlled MUX controller.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called mux-gpio.
+
+endif
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"

@@ -53,6 +53,8 @@ obj-$(CONFIG_ECHO)		+= echo/
 obj-$(CONFIG_VEXPRESS_SYSCFG)	+= vexpress-syscfg.o
 obj-$(CONFIG_CXL_BASE)		+= cxl/
 obj-$(CONFIG_PANEL)             += panel.o
+obj-$(CONFIG_MULTIPLEXER)      	+= mux-core.o
+obj-$(CONFIG_MUX_GPIO)		+= mux-gpio.o
 
 lkdtm-$(CONFIG_LKDTM)		+= lkdtm_core.o
 lkdtm-$(CONFIG_LKDTM)		+= lkdtm_bugs.o

@@ -0,0 +1,325 @@
+/*
+ * Multiplexer subsystem
+ *
+ * Copyright (C) 2016 Axentia Technologies AB
+ *
+ * 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.
+ */
+
+#define pr_fmt(fmt) "mux-core: " fmt
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/idr.h>
+#include <linux/module.h>
+#include <linux/mux.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/slab.h>
+
+static struct bus_type mux_bus_type = {
+	.name = "mux",
+};
+
+static int __init mux_init(void)
+{
+	return bus_register(&mux_bus_type);
+}
+
+static void __exit mux_exit(void)
+{
+	bus_unregister(&mux_bus_type);
+}
+
+static DEFINE_IDA(mux_ida);
+
+static void mux_control_release(struct device *dev)
+{
+	struct mux_control *mux = to_mux_control(dev);
+
+	ida_simple_remove(&mux_ida, mux->id);
+	kfree(mux);
+}
+
+static struct device_type mux_control_type = {
+	.name = "mux-control",
+	.release = mux_control_release,
+};
+
+/**
+ * mux_control_alloc - allocate a mux-control
+ * @sizeof_priv: Size of extra memory area for private use by the caller.
+ *
+ * Returns the new mux-control.
+ */
+struct mux_control *mux_control_alloc(size_t sizeof_priv)
+{
+	struct mux_control *mux;
+
+	mux = kzalloc(sizeof(*mux) + sizeof_priv, GFP_KERNEL);
+	if (!mux)
+		return NULL;
+
+	mux->dev.bus = &mux_bus_type;
+	mux->dev.type = &mux_control_type;
+	device_initialize(&mux->dev);
+	dev_set_drvdata(&mux->dev, mux);
+
+	init_rwsem(&mux->lock);
+
+	mux->id = ida_simple_get(&mux_ida, 0, 0, GFP_KERNEL);
+	if (mux->id < 0) {
+		pr_err("mux-controlX failed to get device id\n");
+		kfree(mux);
+		return NULL;
+	}
+	dev_set_name(&mux->dev, "mux:control%d", mux->id);
+
+	mux->cached_state = -1;
+	mux->idle_state = -1;
+
+	return mux;
+}
+EXPORT_SYMBOL_GPL(mux_control_alloc);
+
+/**
+ * mux_control_register - register a mux-control, thus readying it for use
+ * @mux: The mux-control to register.
+ *
+ * Returns zero on success or a negative errno on error.
+ */
+int mux_control_register(struct mux_control *mux)
+{
+	int ret;
+
+	/* If the calling driver did not initialize of_node, do it here */
+	if (!mux->dev.of_node && mux->dev.parent)
+		mux->dev.of_node = mux->dev.parent->of_node;
+
+	ret = device_add(&mux->dev);
+	if (ret < 0)
+		return ret;
+
+	ret = of_platform_populate(mux->dev.of_node, NULL, NULL, &mux->dev);
+	if (ret < 0)
+		device_del(&mux->dev);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mux_control_register);
+
+/**
+ * mux_control_unregister - take the mux-control off-line, reversing the
+ *			    effexts of mux_control_register
+ * @mux: the mux-control to unregister.
+ */
+void mux_control_unregister(struct mux_control *mux)
+{
+	of_platform_depopulate(&mux->dev);
+	device_del(&mux->dev);
+}
+EXPORT_SYMBOL_GPL(mux_control_unregister);
+
+/**
+ * mux_control_put - put away the mux-control for good, reversing the
+ *		     effects of either mux_control_alloc or mux_control_get
+ * @mux: The mux-control to put away.
+ */
+void mux_control_put(struct mux_control *mux)
+{
+	if (!mux)
+		return;
+	put_device(&mux->dev);
+}
+EXPORT_SYMBOL_GPL(mux_control_put);
+
+static int mux_control_set(struct mux_control *mux, int state)
+{
+	int ret = mux->ops->set(mux, state);
+
+	mux->cached_state = ret < 0 ? -1 : state;
+
+	return ret;
+}
+
+/**
+ * mux_control_select - select the given multiplexer state
+ * @mux: The mux-control to request a change of state from.
+ * @state: The new requested state.
+ *
+ * Returns 0 if the requested state was already active, or 1 it the
+ * mux-control state was changed to the requested state. Or a negavive
+ * errno on error.
+ * Note that the difference in return value of zero or one is of
+ * questionable value; especially if the mux-control has several independent
+ * consumers, which is something the consumers should not be making
+ * assumptions about.
+ *
+ * Make sure to call mux_control_deselect when the operation is complete and
+ * the mux-control is free for others to use, but do not call
+ * mux_control_deselect if mux_control_select fails.
+ */
+int mux_control_select(struct mux_control *mux, int state)
+{
+	int ret;
+
+	if (down_read_trylock(&mux->lock)) {
+		if (mux->cached_state == state)
+			return 0;
+
+		/* Sigh, the mux needs updating... */
+		up_read(&mux->lock);
+	}
+
+	/* ...or it's just contended. */
+	down_write(&mux->lock);
+
+	if (mux->cached_state == state) {
+		/*
+		 * Hmmm, someone else changed the mux to my liking.
+		 * That makes me wonder how long I waited for nothing?
+		 */
+		downgrade_write(&mux->lock);
+		return 0;
+	}
+
+	ret = mux_control_set(mux, state);
+	if (ret < 0) {
+		if (mux->idle_state != -1)
+			mux_control_set(mux, mux->idle_state);
+
+		up_write(&mux->lock);
+		return ret;
+	}
+
+	downgrade_write(&mux->lock);
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(mux_control_select);
+
+/**
+ * mux_control_deselect - deselect the previously selected multiplexer state
+ * @mux: The mux-control to deselect.
+ *
+ * Returns 0 on success and a negative errno on error. An error can only
+ * occur if the mux has an idle state. Note that even if an error occurs, the
+ * mux-control is unlocked for others to access.
+ */
+int mux_control_deselect(struct mux_control *mux)
+{
+	int ret = 0;
+
+	if (mux->idle_state != -1 && mux->cached_state != mux->idle_state)
+		ret = mux_control_set(mux, mux->idle_state);
+
+	up_read(&mux->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mux_control_deselect);
+
+static int of_dev_node_match(struct device *dev, void *data)
+{
+	return dev->of_node == data;
+}
+
+static struct mux_control *of_find_mux_by_node(struct device_node *np)
+{
+	struct device *dev;
+
+	dev = bus_find_device(&mux_bus_type, NULL, np, of_dev_node_match);
+
+	return dev ? to_mux_control(dev) : NULL;
+}
+
+/**
+ * mux_control_get - get the mux-control for a device
+ * @dev: The device that needs a mux-control.
+ *
+ * Returns the mux-control.
+ */
+struct mux_control *mux_control_get(struct device *dev)
+{
+	struct mux_control *mux;
+
+	if (!dev->of_node)
+		return ERR_PTR(-ENODEV);
+
+	mux = of_find_mux_by_node(dev->of_node->parent);
+	if (!mux)
+		return ERR_PTR(-EPROBE_DEFER);
+
+	return mux;
+}
+EXPORT_SYMBOL_GPL(mux_control_get);
+
+static void devm_mux_control_free(struct device *dev, void *res)
+{
+	struct mux_control *mux = *(struct mux_control **)res;
+
+	mux_control_put(mux);
+}
+
+/**
+ * devm_mux_control_get - get the mux-control for a device, with resource
+ *			  management
+ * @dev: The device that needs a mux-control.
+ *
+ * Returns the mux-control.
+ */
+struct mux_control *devm_mux_control_get(struct device *dev)
+{
+	struct mux_control **ptr, *mux;
+
+	ptr = devres_alloc(devm_mux_control_free, sizeof(*ptr), GFP_KERNEL);
+	if (!ptr)
+		return ERR_PTR(-ENOMEM);
+
+	mux = mux_control_get(dev);
+	if (IS_ERR(mux)) {
+		devres_free(ptr);
+		return mux;
+	}
+
+	*ptr = mux;
+	devres_add(dev, ptr);
+
+	return mux;
+}
+EXPORT_SYMBOL_GPL(devm_mux_control_get);
+
+static int devm_mux_control_match(struct device *dev, void *res, void *data)
+{
+	struct mux_control **r = res;
+
+	if (!r || !*r) {
+		WARN_ON(!r || !*r);
+		return 0;
+	}
+
+	return *r == data;
+}
+
+/**
+ * devm_mux_control_put - resource-managed version mux_control_put
+ * @dev: The device that originally got the mux-control.
+ * @mux: The mux-control to put away.
+ *
+ * Note that you do not normally need to call this function.
+ */
+void devm_mux_control_put(struct device *dev, struct mux_control *mux)
+{
+	WARN_ON(devres_release(dev, devm_mux_control_free,
+			       devm_mux_control_match, mux));
+}
+EXPORT_SYMBOL_GPL(devm_mux_control_put);
+
+subsys_initcall(mux_init);
+module_exit(mux_exit);
+
+MODULE_AUTHOR("Peter Rosin <peda@axentia.se");
+MODULE_DESCRIPTION("MUX subsystem");
+MODULE_LICENSE("GPL v2");

@@ -0,0 +1,116 @@
+/*
+ * GPIO-controlled multiplexer driver
+ *
+ * Copyright (C) 2016 Axentia Technologies AB
+ *
+ * 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/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/mux.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+
+struct mux_gpio {
+	struct gpio_descs *gpios;
+};
+
+static int mux_gpio_set(struct mux_control *mux, int val)
+{
+	struct mux_gpio *mux_gpio = mux_control_priv(mux);
+	int i;
+
+	for (i = 0; i < mux_gpio->gpios->ndescs; i++)
+		gpiod_set_value_cansleep(mux_gpio->gpios->desc[i],
+					 val & (1 << i));
+
+	return 0;
+}
+
+static const struct mux_control_ops mux_gpio_ops = {
+	.set = mux_gpio_set,
+};
+
+static const struct of_device_id mux_gpio_dt_ids[] = {
+	{ .compatible = "mux-gpio", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, mux_gpio_dt_ids);
+
+static int mux_gpio_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *np = pdev->dev.of_node;
+	struct mux_control *mux;
+	struct mux_gpio *mux_gpio;
+	u32 idle_state;
+	int ret;
+
+	if (!np)
+		return -ENODEV;
+
+	mux = mux_control_alloc(sizeof(*mux_gpio));
+	if (!mux)
+		return -ENOMEM;
+	mux_gpio = mux_control_priv(mux);
+	mux->dev.parent = dev;
+	mux->ops = &mux_gpio_ops;
+
+	platform_set_drvdata(pdev, mux);
+
+	mux_gpio->gpios = devm_gpiod_get_array(dev, "mux", GPIOD_OUT_LOW);
+	if (IS_ERR(mux_gpio->gpios)) {
+		if (PTR_ERR(mux_gpio->gpios) != -EPROBE_DEFER)
+			dev_err(dev, "failed to get gpios\n");
+		mux_control_put(mux);
+		return PTR_ERR(mux_gpio->gpios);
+	}
+	mux->states = 1 << mux_gpio->gpios->ndescs;
+
+	ret = of_property_read_u32(np, "idle-state", &idle_state);
+	if (ret >= 0) {
+		if (idle_state >= mux->states) {
+			dev_err(dev, "invalid idle-state %u\n", idle_state);
+			return -EINVAL;
+		}
+		mux->idle_state = idle_state;
+	}
+
+	ret = mux_control_register(mux);
+	if (ret < 0) {
+		dev_err(dev, "failed to register mux_control\n");
+		mux_control_put(mux);
+		return ret;
+	}
+
+	return ret;
+}
+
+static int mux_gpio_remove(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct mux_control *mux = to_mux_control(dev);
+
+	mux_control_unregister(mux);
+	mux_control_put(mux);
+	return 0;
+}
+
+static struct platform_driver mux_gpio_driver = {
+	.driver = {
+		.name = "mux-gpio",
+		.of_match_table	= of_match_ptr(mux_gpio_dt_ids),
+	},
+	.probe = mux_gpio_probe,
+	.remove = mux_gpio_remove,
+};
+module_platform_driver(mux_gpio_driver);
+
+MODULE_AUTHOR("Peter Rosin <peda@axentia.se");
+MODULE_DESCRIPTION("GPIO-controlled multiplexer driver");
+MODULE_LICENSE("GPL v2");

@@ -0,0 +1,55 @@
+/*
+ * mux.h - definitions for the multiplexer interface
+ *
+ * Copyright (C) 2016 Axentia Technologies AB
+ *
+ * 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_MUX_H
+#define _LINUX_MUX_H
+
+#include <linux/device.h>
+#include <linux/rwsem.h>
+
+struct mux_control;
+
+struct mux_control_ops {
+	int (*set)(struct mux_control *mux, int reg);
+};
+
+struct mux_control {
+	struct rw_semaphore lock; /* protects the state of the mux */
+
+	struct device dev;
+	int id;
+
+	unsigned int states;
+	int cached_state;
+	int idle_state;
+
+	const struct mux_control_ops *ops;
+};
+
+#define to_mux_control(x) container_of((x), struct mux_control, dev)
+
+static inline void *mux_control_priv(struct mux_control *mux)
+{
+	return mux + 1;
+}
+
+struct mux_control *mux_control_alloc(size_t sizeof_priv);
+int mux_control_register(struct mux_control *mux);
+void mux_control_unregister(struct mux_control *mux);
+void mux_control_put(struct mux_control *mux);
+
+int mux_control_select(struct mux_control *mux, int state);
+int mux_control_deselect(struct mux_control *mux);
+
+struct mux_control *mux_control_get(struct device *dev);
+struct mux_control *devm_mux_control_get(struct device *dev);
+void devm_mux_control_put(struct device *dev, struct mux_control *mux);
+
+#endif /* _LINUX_MUX_H */

@@ -0,0 +1,76 @@
+Common multiplexer controller bindings
+
+A mux controller will have one, or several, child devices that uses (or
+consumes) a mux controller. A mux controller can possibly control several
+parallel multiplexers. The node for a mux controller will have one child
+node for each multiplexer controller consumer.
+
+A mux controller provides a number of states to its consumers, and the
+state space is a simple zero-based enumeration. I.e. 0-1 for a 2-way
+multiplexer, 0-7 for an 8-way multiplexer, etc.
+
+Example:
+
+	/*
+	 * Two consumers (one for an ADC line and one for an i2c bus) of
+	 * parallel 4-way multiplexers controlled by the same two GPIO-lines.
+	 */
+	mux {
+		compatible = "mux-gpio";
+
+		mux-gpios = <&pioA 0 GPIO_ACTIVE_HIGH>,
+			    <&pioA 1 GPIO_ACTIVE_HIGH>;
+
+		adc {
+			compatible = "iio-mux";
+			io-channels = <&adc 0>;
+			io-channel-names = "parent";
+
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			sync-1@0 {
+				reg = <0>;
+			};
+
+			in@1 {
+				reg = <1>;
+			};
+
+			out@2 {
+				reg = <2>;
+			};
+
+			sync-2@3 {
+				reg = <3>;
+			};
+		};
+
+		i2c-mux {
+			compatible = "i2c-mux-simple,mux-locked";
+			i2c-parent = <&i2c1>;
+
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			i2c@0 {
+				reg = <0>;
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				ssd1307: oled@3c {
+					/* ... */
+				};
+			};
+
+			i2c@3 {
+				reg = <3>;
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				pca9555: pca9555@20 {
+					/* ... */
+				};
+			};
+		};
+	};

@@ -0,0 +1,78 @@
+GPIO-based multiplexer controller bindings
+
+Define what GPIO pins are used to control a multiplexer. Or several
+multiplexers, if the same pins control more than one multiplexer.
+
+Required properties:
+- compatible : "mux-gpio"
+- mux-gpios : list of gpios used to control the multiplexer, least
+	      significant bit first.
+* Standard mux-controller bindings as decribed in mux-controller.txt
+
+Optional properties:
+- idle-state : if present, the state the mux will have when idle.
+
+The multiplexer state is defined as the number represented by the
+multiplexer GPIO pins, where the first pin is the least significant
+bit. And active pin is a binary 1, an inactive pin is a binary 0.
+
+Example:
+	mux {
+		compatible = "mux-gpio";
+
+		mux-gpios = <&pioA 0 GPIO_ACTIVE_HIGH>,
+			    <&pioA 1 GPIO_ACTIVE_HIGH>;
+
+		adc {
+			compatible = "iio-mux";
+			io-channels = <&adc 0>;
+			io-channel-names = "parent";
+
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			sync-1@0 {
+				reg = <0>;
+			};
+
+			in@1 {
+				reg = <1>;
+			};
+
+			out@2 {
+				reg = <2>;
+			};
+
+			sync-2@3 {
+				reg = <3>;
+			};
+		};
+
+		i2c-mux {
+			compatible = "i2c-mux-simple,mux-locked";
+			i2c-parent = <&i2c1>;
+
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			i2c@0 {
+				reg = <0>;
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				ssd1307: oled@3c {
+					/* ... */
+				};
+			};
+
+			i2c@3 {
+				reg = <3>;
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				pca9555: pca9555@20 {
+					/* ... */
+				};
+			};
+		};
+	};

@@ -8244,6 +8244,11 @@ S:	Orphan
 F:	drivers/mmc/host/mmc_spi.c
 F:	include/linux/spi/mmc_spi.h
 
+MULTIPLEXER SUBSYSTEM
+M:	Peter Rosin <peda@axentia.se>
+S:	Maintained
+F:	Documentation/devicetree/bindings/misc/mux-*
+
 MULTISOUND SOUND DRIVER
 M:	Andrew Veliath <andrewtv@usa.net>
 S:	Maintained

@@ -6129,6 +6129,7 @@ M:	Peter Rosin <peda@axentia.se>
 L:	linux-iio@vger.kernel.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/iio/multiplexer/iio-mux.txt
+F:	drivers/iio/multiplexer/iio-mux.c
 
 IIO SUBSYSTEM AND DRIVERS
 M:	Jonathan Cameron <jic23@kernel.org>

@@ -82,6 +82,7 @@ source "drivers/iio/humidity/Kconfig"
 source "drivers/iio/imu/Kconfig"
 source "drivers/iio/light/Kconfig"
 source "drivers/iio/magnetometer/Kconfig"
+source "drivers/iio/multiplexer/Kconfig"
 source "drivers/iio/orientation/Kconfig"
 if IIO_TRIGGER
    source "drivers/iio/trigger/Kconfig"

@@ -27,6 +27,7 @@ obj-y += humidity/
 obj-y += imu/
 obj-y += light/
 obj-y += magnetometer/
+obj-y += multiplexer/
 obj-y += orientation/
 obj-y += potentiometer/
 obj-y += pressure/

@@ -0,0 +1,18 @@
+#
+# Multiplexer drivers
+#
+# When adding new entries keep the list in alphabetical order
+
+menu "Multiplexers"
+
+config IIO_MUX
+	tristate "IIO multiplexer driver"
+	select MULTIPLEXER
+	depends on OF
+	help
+	  Say yes here to build support for the IIO multiplexer.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called iio-mux.
+
+endmenu

@@ -0,0 +1,6 @@
+#
+# Makefile for industrial I/O multiplexer drivers
+#
+
+# When adding new entries keep the list in alphabetical order
+obj-$(CONFIG_IIO_MUX) += iio-mux.o

@@ -0,0 +1,450 @@
+/*
+ * IIO multiplexer driver
+ *
+ * Copyright (C) 2016 Axentia Technologies AB
+ *
+ * Author: Peter Rosin <peda@axentia.se>
+ *
+ * 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/err.h>
+#include <linux/iio/consumer.h>
+#include <linux/iio/iio.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/mux.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+struct mux_ext_info_cache {
+	char *data;
+	size_t size;
+};
+
+struct mux_child {
+	struct mux_ext_info_cache *ext_info_cache;
+};
+
+struct mux {
+	int cached_state;
+	struct mux_control *control;
+	struct iio_channel *parent;
+	struct iio_dev *indio_dev;
+	struct iio_chan_spec *chan;
+	struct iio_chan_spec_ext_info *ext_info;
+	struct mux_child *child;
+};
+
+static int iio_mux_select(struct mux *mux, int idx)
+{
+	struct mux_child *child = &mux->child[idx];
+	struct iio_chan_spec const *chan = &mux->chan[idx];
+	int ret;
+	int i;
+
+	ret = mux_control_select(mux->control, chan->channel);
+	if (ret < 0) {
+		mux->cached_state = -1;
+		return ret;
+	}
+
+	if (mux->cached_state == chan->channel)
+		return 0;
+
+	if (chan->ext_info) {
+		for (i = 0; chan->ext_info[i].name; ++i) {
+			const char *attr = chan->ext_info[i].name;
+			struct mux_ext_info_cache *cache;
+
+			cache = &child->ext_info_cache[i];
+
+			if (cache->size < 0)
+				continue;
+
+			ret = iio_write_channel_ext_info(mux->parent, attr,
+							 cache->data,
+							 cache->size);
+
+			if (ret < 0) {
+				mux_control_deselect(mux->control);
+				mux->cached_state = -1;
+				return ret;
+			}
+		}
+	}
+	mux->cached_state = chan->channel;
+
+	return 0;
+}
+
+static void iio_mux_deselect(struct mux *mux)
+{
+	mux_control_deselect(mux->control);
+}
+
+static int mux_read_raw(struct iio_dev *indio_dev,
+			struct iio_chan_spec const *chan,
+			int *val, int *val2, long mask)
+{
+	struct mux *mux = iio_priv(indio_dev);
+	int idx = chan - mux->chan;
+	int ret;
+
+	ret = iio_mux_select(mux, idx);
+	if (ret < 0)
+		return ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = iio_read_channel_raw(mux->parent, val);
+		break;
+
+	case IIO_CHAN_INFO_SCALE:
+		ret = iio_read_channel_scale(mux->parent, val, val2);
+		break;
+
+	default:
+		ret = -EINVAL;
+	}
+
+	iio_mux_deselect(mux);
+
+	return ret;
+}
+
+static int mux_read_avail(struct iio_dev *indio_dev,
+			  struct iio_chan_spec const *chan,
+			  const int **vals, int *type, int *length,
+			  long mask)
+{
+	struct mux *mux = iio_priv(indio_dev);
+	int idx = chan - mux->chan;
+	int ret;
+
+	ret = iio_mux_select(mux, idx);
+	if (ret < 0)
+		return ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		*type = IIO_VAL_INT;
+		ret = iio_read_avail_channel_raw(mux->parent, vals, length);
+		break;
+
+	default:
+		ret = -EINVAL;
+	}
+
+	iio_mux_deselect(mux);
+
+	return ret;
+}
+
+static int mux_write_raw(struct iio_dev *indio_dev,
+			 struct iio_chan_spec const *chan,
+			 int val, int val2, long mask)
+{
+	struct mux *mux = iio_priv(indio_dev);
+	int idx = chan - mux->chan;
+	int ret;
+
+	ret = iio_mux_select(mux, idx);
+	if (ret < 0)
+		return ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = iio_write_channel_raw(mux->parent, val);
+		break;
+
+	default:
+		ret = -EINVAL;
+	}
+
+	iio_mux_deselect(mux);
+
+	return ret;
+}
+
+static const struct iio_info mux_info = {
+	.read_raw = mux_read_raw,
+	.read_avail = mux_read_avail,
+	.write_raw = mux_write_raw,
+	.driver_module = THIS_MODULE,
+};
+
+static ssize_t mux_read_ext_info(struct iio_dev *indio_dev, uintptr_t private,
+				 struct iio_chan_spec const *chan, char *buf)
+{
+	struct mux *mux = iio_priv(indio_dev);
+	int idx = chan - mux->chan;
+	ssize_t ret;
+
+	ret = iio_mux_select(mux, idx);
+	if (ret < 0)
+		return ret;
+
+	ret = iio_read_channel_ext_info(mux->parent,
+					mux->ext_info[private].name,
+					buf);
+
+	iio_mux_deselect(mux);
+
+	return ret;
+}
+
+static ssize_t mux_write_ext_info(struct iio_dev *indio_dev, uintptr_t private,
+				  struct iio_chan_spec const *chan,
+				  const char *buf, size_t len)
+{
+	struct device *dev = indio_dev->dev.parent;
+	struct mux *mux = iio_priv(indio_dev);
+	int idx = chan - mux->chan;
+	char *new;
+	ssize_t ret;
+
+	ret = iio_mux_select(mux, idx);
+	if (ret < 0)
+		return ret;
+
+	new = devm_kmemdup(dev, buf, len + 1, GFP_KERNEL);
+	if (!new) {
+		iio_mux_deselect(mux);
+		return -ENOMEM;
+	}
+
+	new[len] = 0;
+
+	ret = iio_write_channel_ext_info(mux->parent,
+					 mux->ext_info[private].name,
+					 buf, len);
+	if (ret < 0) {
+		iio_mux_deselect(mux);
+		devm_kfree(dev, new);
+		return ret;
+	}
+
+	devm_kfree(dev, mux->child[idx].ext_info_cache[private].data);
+	mux->child[idx].ext_info_cache[private].data = new;
+	mux->child[idx].ext_info_cache[private].size = len;
+
+	iio_mux_deselect(mux);
+
+	return ret;
+}
+
+static int mux_configure_channel(struct device *dev, struct mux *mux,
+				 struct device_node *child_np, int idx)
+{
+	struct mux_child *child = &mux->child[idx];
+	struct iio_chan_spec *chan = &mux->chan[idx];
+	struct iio_chan_spec const *pchan = mux->parent->channel;
+	u32 state;
+	char *page = NULL;
+	int num_ext_info;
+	int i;
+	int ret;
+
+	chan->indexed = 1;
+	chan->output = pchan->output;
+	chan->datasheet_name = child_np->name;
+	chan->ext_info = mux->ext_info;
+
+	ret = iio_get_channel_type(mux->parent, &chan->type);
+	if (ret < 0) {
+		dev_err(dev, "failed to get parent channel type\n");
+		return ret;
+	}
+
+	if (iio_channel_has_info(pchan, IIO_CHAN_INFO_RAW))
+		chan->info_mask_separate |= BIT(IIO_CHAN_INFO_RAW);
+	if (iio_channel_has_info(pchan, IIO_CHAN_INFO_SCALE))
+		chan->info_mask_separate |= BIT(IIO_CHAN_INFO_SCALE);
+
+	if (iio_channel_has_available(pchan, IIO_CHAN_INFO_RAW))
+		chan->info_mask_separate_available |= BIT(IIO_CHAN_INFO_RAW);
+
+	ret = of_property_read_u32(child_np, "reg", &state);
+	if (ret < 0) {
+		dev_err(dev, "no reg property for node '%s'\n", child_np->name);
+		return ret;
+	}
+
+	if (state >= mux->control->states) {
+		dev_err(dev, "invalid reg %u\n", state);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < idx; ++i) {
+		if (mux->chan[i].channel == state) {
+			dev_err(dev, "double use of reg %u\n", state);
+			return -EINVAL;
+		}
+	}
+
+	chan->channel = state;
+
+	num_ext_info = iio_get_channel_ext_info_count(mux->parent);
+	if (num_ext_info) {
+		page = devm_kzalloc(dev, PAGE_SIZE, GFP_KERNEL);
+		if (!page)
+			return -ENOMEM;
+	}
+	child->ext_info_cache = devm_kzalloc(dev,
+					     sizeof(*child->ext_info_cache) *
+					     num_ext_info, GFP_KERNEL);
+	for (i = 0; i < num_ext_info; ++i) {
+		child->ext_info_cache[i].size = -1;
+
+		if (!pchan->ext_info[i].write)
+			continue;
+		if (!pchan->ext_info[i].read)
+			continue;
+
+		ret = iio_read_channel_ext_info(mux->parent,
+						mux->ext_info[i].name,
+						page);
+		if (ret < 0) {
+			dev_err(dev, "failed to get ext_info '%s'\n",
+				pchan->ext_info[i].name);
+			return ret;
+		}
+		if (ret >= PAGE_SIZE) {
+			dev_err(dev, "too large ext_info '%s'\n",
+				pchan->ext_info[i].name);
+			return -EINVAL;
+		}
+
+		child->ext_info_cache[i].data = devm_kmemdup(dev, page, ret + 1,
+							     GFP_KERNEL);
+		child->ext_info_cache[i].data[ret] = 0;
+		child->ext_info_cache[i].size = ret;
+	}
+
+	if (page)
+		devm_kfree(dev, page);
+
+	return 0;
+}
+
+static int mux_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *np = pdev->dev.of_node;
+	struct device_node *child_np;
+	struct iio_dev *indio_dev;
+	struct iio_channel *parent;
+	struct mux *mux;
+	int sizeof_ext_info;
+	int children;
+	int sizeof_priv;
+	int i;
+	int ret;
+
+	if (!np)
+		return -ENODEV;
+
+	parent = devm_iio_channel_get(dev, "parent");
+	if (IS_ERR(parent)) {
+		if (PTR_ERR(parent) != -EPROBE_DEFER)
+			dev_err(dev, "failed to get parent channel\n");
+		return PTR_ERR(parent);
+	}
+
+	sizeof_ext_info = iio_get_channel_ext_info_count(parent);
+	if (sizeof_ext_info) {
+		sizeof_ext_info += 1; /* one extra entry for the sentinel */
+		sizeof_ext_info *= sizeof(*mux->ext_info);
+	}
+
+	children = of_get_child_count(np);
+	if (children <= 0) {
+		dev_err(dev, "not even a single child\n");
+		return -EINVAL;
+	}
+
+	sizeof_priv = sizeof(*mux);
+	sizeof_priv += sizeof(*mux->child) * children;
+	sizeof_priv += sizeof(*mux->chan) * children;
+	sizeof_priv += sizeof_ext_info;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof_priv);
+	if (!indio_dev)
+		return -ENOMEM;
+
+	mux = iio_priv(indio_dev);
+	mux->child = (struct mux_child *)(mux + 1);
+	mux->chan = (struct iio_chan_spec *)(mux->child + children);
+
+	platform_set_drvdata(pdev, indio_dev);
+
+	mux->parent = parent;
+	mux->cached_state = -1;
+
+	indio_dev->name = dev_name(dev);
+	indio_dev->dev.parent = dev;
+	indio_dev->info = &mux_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = mux->chan;
+	indio_dev->num_channels = children;
+	if (sizeof_ext_info) {
+		mux->ext_info = devm_kmemdup(dev,
+					     parent->channel->ext_info,
+					     sizeof_ext_info, GFP_KERNEL);
+		if (!mux->ext_info)
+			return -ENOMEM;
+
+		for (i = 0; mux->ext_info[i].name; ++i) {
+			if (parent->channel->ext_info[i].read)
+				mux->ext_info[i].read = mux_read_ext_info;
+			if (parent->channel->ext_info[i].write)
+				mux->ext_info[i].write = mux_write_ext_info;
+			mux->ext_info[i].private = i;
+		}
+	}
+
+	mux->control = devm_mux_control_get(dev);
+	if (IS_ERR(mux->control)) {
+		if (PTR_ERR(mux->control) != -EPROBE_DEFER)
+			dev_err(dev, "failed to get control-mux\n");
+		return PTR_ERR(mux->control);
+	}
+
+	i = 0;
+	for_each_child_of_node(np, child_np) {
+		ret = mux_configure_channel(dev, mux, child_np, i);
+		if (ret < 0)
+			return ret;
+		i++;
+	}
+
+	ret = devm_iio_device_register(dev, indio_dev);
+	if (ret) {
+		dev_err(dev, "failed to register iio device\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct of_device_id mux_match[] = {
+	{ .compatible = "iio-mux" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, mux_match);
+
+static struct platform_driver mux_driver = {
+	.probe = mux_probe,
+	.driver = {
+		.name = "iio-mux",
+		.of_match_table = mux_match,
+	},
+};
+module_platform_driver(mux_driver);
+
+MODULE_DESCRIPTION("IIO multiplexer driver");
+MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
+MODULE_LICENSE("GPL v2");