drivers/mux/core.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Multiplexer subsystem
  *
  * Copyright (C) 2017 Axentia Technologies AB
  *
  * Author: Peter Rosin <peda@axentia.se>
  */

 #define pr_fmt(fmt) "mux-core: " fmt

 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/export.h>
 #include <linux/idr.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/mux/consumer.h>
 #include <linux/mux/driver.h>
 #include <linux/of.h>
 #include <linux/of_platform.h>
 #include <linux/slab.h>

 /*
  * The idle-as-is "state" is not an actual state that may be selected, it
  * only implies that the state should not be changed. So, use that state
  * as indication that the cached state of the multiplexer is unknown.
  */
 #define MUX_CACHE_UNKNOWN MUX_IDLE_AS_IS

 static struct class mux_class = {
 	.name = "mux",
 	.owner = THIS_MODULE,
 };

 static DEFINE_IDA(mux_ida);

 static int __init mux_init(void)
 {
 	ida_init(&mux_ida);
 	return class_register(&mux_class);
 }

 static void __exit mux_exit(void)
 {
 	class_unregister(&mux_class);
 	ida_destroy(&mux_ida);
 }

 static void mux_chip_release(struct device *dev)
 {
 	struct mux_chip *mux_chip = to_mux_chip(dev);

 	ida_simple_remove(&mux_ida, mux_chip->id);
 	kfree(mux_chip);
 }

 static const struct device_type mux_type = {
 	.name = "mux-chip",
 	.release = mux_chip_release,
 };

 /**
  * mux_chip_alloc() - Allocate a mux-chip.
  * @dev: The parent device implementing the mux interface.
  * @controllers: The number of mux controllers to allocate for this chip.
  * @sizeof_priv: Size of extra memory area for private use by the caller.
  *
  * After allocating the mux-chip with the desired number of mux controllers
  * but before registering the chip, the mux driver is required to configure
  * the number of valid mux states in the mux_chip->mux[N].states members and
  * the desired idle state in the returned mux_chip->mux[N].idle_state members.
  * The default idle state is MUX_IDLE_AS_IS. The mux driver also needs to
  * provide a pointer to the operations struct in the mux_chip->ops member
  * before registering the mux-chip with mux_chip_register.
  *
  * Return: A pointer to the new mux-chip, or an ERR_PTR with a negative errno.
  */
 struct mux_chip *mux_chip_alloc(struct device *dev,
 				unsigned int controllers, size_t sizeof_priv)
 {
 	struct mux_chip *mux_chip;
 	int i;

 	if (WARN_ON(!dev || !controllers))
 		return ERR_PTR(-EINVAL);

 	mux_chip = kzalloc(sizeof(*mux_chip) +
 			   controllers * sizeof(*mux_chip->mux) +
 			   sizeof_priv, GFP_KERNEL);
 	if (!mux_chip)
 		return ERR_PTR(-ENOMEM);

 	mux_chip->mux = (struct mux_control *)(mux_chip + 1);
 	mux_chip->dev.class = &mux_class;
 	mux_chip->dev.type = &mux_type;
 	mux_chip->dev.parent = dev;
 	mux_chip->dev.of_node = dev->of_node;
 	dev_set_drvdata(&mux_chip->dev, mux_chip);

 	mux_chip->id = ida_simple_get(&mux_ida, 0, 0, GFP_KERNEL);
 	if (mux_chip->id < 0) {
 		int err = mux_chip->id;

 		pr_err("muxchipX failed to get a device id\n");
 		kfree(mux_chip);
 		return ERR_PTR(err);
 	}
 	dev_set_name(&mux_chip->dev, "muxchip%d", mux_chip->id);

 	mux_chip->controllers = controllers;
 	for (i = 0; i < controllers; ++i) {
 		struct mux_control *mux = &mux_chip->mux[i];

 		mux->chip = mux_chip;
 		sema_init(&mux->lock, 1);
 		mux->cached_state = MUX_CACHE_UNKNOWN;
 		mux->idle_state = MUX_IDLE_AS_IS;
 	}

 	device_initialize(&mux_chip->dev);

 	return mux_chip;
 }
 EXPORT_SYMBOL_GPL(mux_chip_alloc);

 static int mux_control_set(struct mux_control *mux, int state)
 {
 	int ret = mux->chip->ops->set(mux, state);

 	mux->cached_state = ret < 0 ? MUX_CACHE_UNKNOWN : state;

 	return ret;
 }

 /**
  * mux_chip_register() - Register a mux-chip, thus readying the controllers
  *			 for use.
  * @mux_chip: The mux-chip to register.
  *
  * Do not retry registration of the same mux-chip on failure. You should
  * instead put it away with mux_chip_free() and allocate a new one, if you
  * for some reason would like to retry registration.
  *
  * Return: Zero on success or a negative errno on error.
  */
 int mux_chip_register(struct mux_chip *mux_chip)
 {
 	int i;
 	int ret;

 	for (i = 0; i < mux_chip->controllers; ++i) {
 		struct mux_control *mux = &mux_chip->mux[i];

 		if (mux->idle_state == mux->cached_state)
 			continue;

 		ret = mux_control_set(mux, mux->idle_state);
 		if (ret < 0) {
 			dev_err(&mux_chip->dev, "unable to set idle state\n");
 			return ret;
 		}
 	}

 	ret = device_add(&mux_chip->dev);
 	if (ret < 0)
 		dev_err(&mux_chip->dev,
 			"device_add failed in %s: %d\n", __func__, ret);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(mux_chip_register);

 /**
  * mux_chip_unregister() - Take the mux-chip off-line.
  * @mux_chip: The mux-chip to unregister.
  *
  * mux_chip_unregister() reverses the effects of mux_chip_register().
  * But not completely, you should not try to call mux_chip_register()
  * on a mux-chip that has been registered before.
  */
 void mux_chip_unregister(struct mux_chip *mux_chip)
 {
 	device_del(&mux_chip->dev);
 }
 EXPORT_SYMBOL_GPL(mux_chip_unregister);

 /**
  * mux_chip_free() - Free the mux-chip for good.
  * @mux_chip: The mux-chip to free.
  *
  * mux_chip_free() reverses the effects of mux_chip_alloc().
  */
 void mux_chip_free(struct mux_chip *mux_chip)
 {
 	if (!mux_chip)
 		return;

 	put_device(&mux_chip->dev);
 }
 EXPORT_SYMBOL_GPL(mux_chip_free);

 static void devm_mux_chip_release(struct device *dev, void *res)
 {
 	struct mux_chip *mux_chip = *(struct mux_chip **)res;

 	mux_chip_free(mux_chip);
 }

 /**
  * devm_mux_chip_alloc() - Resource-managed version of mux_chip_alloc().
  * @dev: The parent device implementing the mux interface.
  * @controllers: The number of mux controllers to allocate for this chip.
  * @sizeof_priv: Size of extra memory area for private use by the caller.
  *
  * See mux_chip_alloc() for more details.
  *
  * Return: A pointer to the new mux-chip, or an ERR_PTR with a negative errno.
  */
 struct mux_chip *devm_mux_chip_alloc(struct device *dev,
 				     unsigned int controllers,
 				     size_t sizeof_priv)
 {
 	struct mux_chip **ptr, *mux_chip;

 	ptr = devres_alloc(devm_mux_chip_release, sizeof(*ptr), GFP_KERNEL);
 	if (!ptr)
 		return ERR_PTR(-ENOMEM);

 	mux_chip = mux_chip_alloc(dev, controllers, sizeof_priv);
 	if (IS_ERR(mux_chip)) {
 		devres_free(ptr);
 		return mux_chip;
 	}

 	*ptr = mux_chip;
 	devres_add(dev, ptr);

 	return mux_chip;
 }
 EXPORT_SYMBOL_GPL(devm_mux_chip_alloc);

 static void devm_mux_chip_reg_release(struct device *dev, void *res)
 {
 	struct mux_chip *mux_chip = *(struct mux_chip **)res;

 	mux_chip_unregister(mux_chip);
 }

 /**
  * devm_mux_chip_register() - Resource-managed version mux_chip_register().
  * @dev: The parent device implementing the mux interface.
  * @mux_chip: The mux-chip to register.
  *
  * See mux_chip_register() for more details.
  *
  * Return: Zero on success or a negative errno on error.
  */
 int devm_mux_chip_register(struct device *dev,
 			   struct mux_chip *mux_chip)
 {
 	struct mux_chip **ptr;
 	int res;

 	ptr = devres_alloc(devm_mux_chip_reg_release, sizeof(*ptr), GFP_KERNEL);
 	if (!ptr)
 		return -ENOMEM;

 	res = mux_chip_register(mux_chip);
 	if (res) {
 		devres_free(ptr);
 		return res;
 	}

 	*ptr = mux_chip;
 	devres_add(dev, ptr);

 	return res;
 }
 EXPORT_SYMBOL_GPL(devm_mux_chip_register);

 /**
  * mux_control_states() - Query the number of multiplexer states.
  * @mux: The mux-control to query.
  *
  * Return: The number of multiplexer states.
  */
 unsigned int mux_control_states(struct mux_control *mux)
 {
 	return mux->states;
 }
 EXPORT_SYMBOL_GPL(mux_control_states);

 /*
  * The mux->lock must be down when calling this function.
  */
 static int __mux_control_select(struct mux_control *mux, int state)
 {
 	int ret;

 	if (WARN_ON(state < 0 || state >= mux->states))
 		return -EINVAL;

 	if (mux->cached_state == state)
 		return 0;

 	ret = mux_control_set(mux, state);
 	if (ret >= 0)
 		return 0;

 	/* The mux update failed, try to revert if appropriate... */
 	if (mux->idle_state != MUX_IDLE_AS_IS)
 		mux_control_set(mux, mux->idle_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.
  *
  * On successfully selecting the mux-control state, it will be locked until
  * there is a call to mux_control_deselect(). If the mux-control is already
  * selected when mux_control_select() is called, the caller will be blocked
  * until mux_control_deselect() is called (by someone else).
  *
  * Therefore, 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.
  *
  * Return: 0 when the mux-control state has the requested state or a negative
  * errno on error.
  */
 int mux_control_select(struct mux_control *mux, unsigned int state)
 {
 	int ret;

 	ret = down_killable(&mux->lock);
 	if (ret < 0)
 		return ret;

 	ret = __mux_control_select(mux, state);

 	if (ret < 0)
 		up(&mux->lock);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(mux_control_select);

 /**
  * mux_control_try_select() - Try to select the given multiplexer state.
  * @mux: The mux-control to request a change of state from.
  * @state: The new requested state.
  *
  * On successfully selecting the mux-control state, it will be locked until
  * mux_control_deselect() called.
  *
  * Therefore, 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_try_select() fails.
  *
  * Return: 0 when the mux-control state has the requested state or a negative
  * errno on error. Specifically -EBUSY if the mux-control is contended.
  */
 int mux_control_try_select(struct mux_control *mux, unsigned int state)
 {
 	int ret;

 	if (down_trylock(&mux->lock))
 		return -EBUSY;

 	ret = __mux_control_select(mux, state);

 	if (ret < 0)
 		up(&mux->lock);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(mux_control_try_select);

 /**
  * mux_control_deselect() - Deselect the previously selected multiplexer state.
  * @mux: The mux-control to deselect.
  *
  * It is required that a single call is made to mux_control_deselect() for
  * each and every successful call made to either of mux_control_select() or
  * mux_control_try_select().
  *
  * Return: 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 and is thus free for the next access.
  */
 int mux_control_deselect(struct mux_control *mux)
 {
 	int ret = 0;

 	if (mux->idle_state != MUX_IDLE_AS_IS &&
 	    mux->idle_state != mux->cached_state)
 		ret = mux_control_set(mux, mux->idle_state);

 	up(&mux->lock);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(mux_control_deselect);

 /* Note this function returns a reference to the mux_chip dev. */
 static struct mux_chip *of_find_mux_chip_by_node(struct device_node *np)
 {
 	struct device *dev;

 	dev = class_find_device_by_of_node(&mux_class, np);

 	return dev ? to_mux_chip(dev) : NULL;
 }

 /**
  * mux_control_get() - Get the mux-control for a device.
  * @dev: The device that needs a mux-control.
  * @mux_name: The name identifying the mux-control.
  *
  * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno.
  */
 struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
 {
 	struct device_node *np = dev->of_node;
 	struct of_phandle_args args;
 	struct mux_chip *mux_chip;
 	unsigned int controller;
 	int index = 0;
 	int ret;

 	if (mux_name) {
 		index = of_property_match_string(np, "mux-control-names",
 						 mux_name);
 		if (index < 0) {
 			dev_err(dev, "mux controller '%s' not found\n",
 				mux_name);
 			return ERR_PTR(index);
 		}
 	}

 	ret = of_parse_phandle_with_args(np,
 					 "mux-controls", "#mux-control-cells",
 					 index, &args);
 	if (ret) {
 		dev_err(dev, "%pOF: failed to get mux-control %s(%i)\n",
 			np, mux_name ?: "", index);
 		return ERR_PTR(ret);
 	}

 	mux_chip = of_find_mux_chip_by_node(args.np);
 	of_node_put(args.np);
 	if (!mux_chip)
 		return ERR_PTR(-EPROBE_DEFER);

 	if (args.args_count > 1 ||
 	    (!args.args_count && (mux_chip->controllers > 1))) {
 		dev_err(dev, "%pOF: wrong #mux-control-cells for %pOF\n",
 			np, args.np);
 		put_device(&mux_chip->dev);
 		return ERR_PTR(-EINVAL);
 	}

 	controller = 0;
 	if (args.args_count)
 		controller = args.args[0];

 	if (controller >= mux_chip->controllers) {
 		dev_err(dev, "%pOF: bad mux controller %u specified in %pOF\n",
 			np, controller, args.np);
 		put_device(&mux_chip->dev);
 		return ERR_PTR(-EINVAL);
 	}

 	return &mux_chip->mux[controller];
 }
 EXPORT_SYMBOL_GPL(mux_control_get);

 /**
  * mux_control_put() - Put away the mux-control for good.
  * @mux: The mux-control to put away.
  *
  * mux_control_put() reverses the effects of mux_control_get().
  */
 void mux_control_put(struct mux_control *mux)
 {
 	put_device(&mux->chip->dev);
 }
 EXPORT_SYMBOL_GPL(mux_control_put);

 static void devm_mux_control_release(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.
  * @mux_name: The name identifying the mux-control.
  *
  * Return: Pointer to the mux-control, or an ERR_PTR with a negative errno.
  */
 struct mux_control *devm_mux_control_get(struct device *dev,
 					 const char *mux_name)
 {
 	struct mux_control **ptr, *mux;

 	ptr = devres_alloc(devm_mux_control_release, sizeof(*ptr), GFP_KERNEL);
 	if (!ptr)
 		return ERR_PTR(-ENOMEM);

 	mux = mux_control_get(dev, mux_name);
 	if (IS_ERR(mux)) {
 		devres_free(ptr);
 		return mux;
 	}

 	*ptr = mux;
 	devres_add(dev, ptr);

 	return mux;
 }
 EXPORT_SYMBOL_GPL(devm_mux_control_get);

 /*
  * Using subsys_initcall instead of module_init here to try to ensure - for
  * the non-modular case - that the subsystem is initialized when mux consumers
  * and mux controllers start to use it.
  * For the modular case, the ordering is ensured with module dependencies.
  */
 subsys_initcall(mux_init);
 module_exit(mux_exit);

 MODULE_DESCRIPTION("Multiplexer subsystem");
 MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
 MODULE_LICENSE("GPL v2");
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Multiplexer subsystem
	*
	* Copyright (C) 2017 Axentia Technologies AB
	*
	* Author: Peter Rosin <peda@axentia.se>
	*/

	#define pr_fmt(fmt) "mux-core: " fmt

	#include <linux/device.h>
	#include <linux/err.h>
	#include <linux/export.h>
	#include <linux/idr.h>
	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/mux/consumer.h>
	#include <linux/mux/driver.h>
	#include <linux/of.h>
	#include <linux/of_platform.h>
	#include <linux/slab.h>

	/*
	* The idle-as-is "state" is not an actual state that may be selected, it
	* only implies that the state should not be changed. So, use that state
	* as indication that the cached state of the multiplexer is unknown.
	*/
	#define MUX_CACHE_UNKNOWN MUX_IDLE_AS_IS

	static struct class mux_class = {
	.name = "mux",
	.owner = THIS_MODULE,
	};

	static DEFINE_IDA(mux_ida);

	static int __init mux_init(void)
	{
	ida_init(&mux_ida);
	return class_register(&mux_class);
	}

	static void __exit mux_exit(void)
	{
	class_unregister(&mux_class);
	ida_destroy(&mux_ida);
	}

	static void mux_chip_release(struct device *dev)
	{
	struct mux_chip *mux_chip = to_mux_chip(dev);

	ida_simple_remove(&mux_ida, mux_chip->id);
	kfree(mux_chip);
	}

	static const struct device_type mux_type = {
	.name = "mux-chip",
	.release = mux_chip_release,
	};

	/**
	* mux_chip_alloc() - Allocate a mux-chip.
	* @dev: The parent device implementing the mux interface.
	* @controllers: The number of mux controllers to allocate for this chip.
	* @sizeof_priv: Size of extra memory area for private use by the caller.
	*
	* After allocating the mux-chip with the desired number of mux controllers
	* but before registering the chip, the mux driver is required to configure
	* the number of valid mux states in the mux_chip->mux[N].states members and
	* the desired idle state in the returned mux_chip->mux[N].idle_state members.
	* The default idle state is MUX_IDLE_AS_IS. The mux driver also needs to
	* provide a pointer to the operations struct in the mux_chip->ops member
	* before registering the mux-chip with mux_chip_register.
	*
	* Return: A pointer to the new mux-chip, or an ERR_PTR with a negative errno.
	*/
	struct mux_chip mux_chip_alloc(struct device dev,
	unsigned int controllers, size_t sizeof_priv)
	{
	struct mux_chip *mux_chip;
	int i;

	if (WARN_ON(!dev \|\| !controllers))
	return ERR_PTR(-EINVAL);

	mux_chip = kzalloc(sizeof(*mux_chip) +
	controllers * sizeof(*mux_chip->mux) +
	sizeof_priv, GFP_KERNEL);
	if (!mux_chip)
	return ERR_PTR(-ENOMEM);

	mux_chip->mux = (struct mux_control *)(mux_chip + 1);
	mux_chip->dev.class = &mux_class;
	mux_chip->dev.type = &mux_type;
	mux_chip->dev.parent = dev;
	mux_chip->dev.of_node = dev->of_node;
	dev_set_drvdata(&mux_chip->dev, mux_chip);

	mux_chip->id = ida_simple_get(&mux_ida, 0, 0, GFP_KERNEL);
	if (mux_chip->id < 0) {
	int err = mux_chip->id;

	pr_err("muxchipX failed to get a device id\n");
	kfree(mux_chip);
	return ERR_PTR(err);
	}
	dev_set_name(&mux_chip->dev, "muxchip%d", mux_chip->id);

	mux_chip->controllers = controllers;
	for (i = 0; i < controllers; ++i) {
	struct mux_control *mux = &mux_chip->mux[i];

	mux->chip = mux_chip;
	sema_init(&mux->lock, 1);
	mux->cached_state = MUX_CACHE_UNKNOWN;
	mux->idle_state = MUX_IDLE_AS_IS;
	}

	device_initialize(&mux_chip->dev);

	return mux_chip;
	}
	EXPORT_SYMBOL_GPL(mux_chip_alloc);

	static int mux_control_set(struct mux_control *mux, int state)
	{
	int ret = mux->chip->ops->set(mux, state);

	mux->cached_state = ret < 0 ? MUX_CACHE_UNKNOWN : state;

	return ret;
	}

	/**
	* mux_chip_register() - Register a mux-chip, thus readying the controllers
	* for use.
	* @mux_chip: The mux-chip to register.
	*
	* Do not retry registration of the same mux-chip on failure. You should
	* instead put it away with mux_chip_free() and allocate a new one, if you
	* for some reason would like to retry registration.
	*
	* Return: Zero on success or a negative errno on error.
	*/
	int mux_chip_register(struct mux_chip *mux_chip)
	{
	int i;
	int ret;

	for (i = 0; i < mux_chip->controllers; ++i) {
	struct mux_control *mux = &mux_chip->mux[i];

	if (mux->idle_state == mux->cached_state)
	continue;

	ret = mux_control_set(mux, mux->idle_state);
	if (ret < 0) {
	dev_err(&mux_chip->dev, "unable to set idle state\n");
	return ret;
	}
	}

	ret = device_add(&mux_chip->dev);
	if (ret < 0)
	dev_err(&mux_chip->dev,
	"device_add failed in %s: %d\n", __func__, ret);
	return ret;
	}
	EXPORT_SYMBOL_GPL(mux_chip_register);

	/**
	* mux_chip_unregister() - Take the mux-chip off-line.
	* @mux_chip: The mux-chip to unregister.
	*
	* mux_chip_unregister() reverses the effects of mux_chip_register().
	* But not completely, you should not try to call mux_chip_register()
	* on a mux-chip that has been registered before.
	*/
	void mux_chip_unregister(struct mux_chip *mux_chip)
	{
	device_del(&mux_chip->dev);
	}
	EXPORT_SYMBOL_GPL(mux_chip_unregister);

	/**
	* mux_chip_free() - Free the mux-chip for good.
	* @mux_chip: The mux-chip to free.
	*
	* mux_chip_free() reverses the effects of mux_chip_alloc().
	*/
	void mux_chip_free(struct mux_chip *mux_chip)
	{
	if (!mux_chip)
	return;

	put_device(&mux_chip->dev);
	}
	EXPORT_SYMBOL_GPL(mux_chip_free);

	static void devm_mux_chip_release(struct device dev, void res)
	{
	struct mux_chip mux_chip = (struct mux_chip **)res;

	mux_chip_free(mux_chip);
	}

	/**
	* devm_mux_chip_alloc() - Resource-managed version of mux_chip_alloc().
	* @dev: The parent device implementing the mux interface.
	* @controllers: The number of mux controllers to allocate for this chip.
	* @sizeof_priv: Size of extra memory area for private use by the caller.
	*
	* See mux_chip_alloc() for more details.
	*
	* Return: A pointer to the new mux-chip, or an ERR_PTR with a negative errno.
	*/
	struct mux_chip devm_mux_chip_alloc(struct device dev,
	unsigned int controllers,
	size_t sizeof_priv)
	{
	struct mux_chip *ptr, mux_chip;

	ptr = devres_alloc(devm_mux_chip_release, sizeof(*ptr), GFP_KERNEL);
	if (!ptr)
	return ERR_PTR(-ENOMEM);

	mux_chip = mux_chip_alloc(dev, controllers, sizeof_priv);
	if (IS_ERR(mux_chip)) {
	devres_free(ptr);
	return mux_chip;
	}

	*ptr = mux_chip;
	devres_add(dev, ptr);

	return mux_chip;
	}
	EXPORT_SYMBOL_GPL(devm_mux_chip_alloc);

	static void devm_mux_chip_reg_release(struct device dev, void res)
	{
	struct mux_chip mux_chip = (struct mux_chip **)res;

	mux_chip_unregister(mux_chip);
	}

	/**
	* devm_mux_chip_register() - Resource-managed version mux_chip_register().
	* @dev: The parent device implementing the mux interface.
	* @mux_chip: The mux-chip to register.
	*
	* See mux_chip_register() for more details.
	*
	* Return: Zero on success or a negative errno on error.
	*/
	int devm_mux_chip_register(struct device *dev,
	struct mux_chip *mux_chip)
	{
	struct mux_chip **ptr;
	int res;

	ptr = devres_alloc(devm_mux_chip_reg_release, sizeof(*ptr), GFP_KERNEL);
	if (!ptr)
	return -ENOMEM;

	res = mux_chip_register(mux_chip);
	if (res) {
	devres_free(ptr);
	return res;
	}

	*ptr = mux_chip;
	devres_add(dev, ptr);

	return res;
	}
	EXPORT_SYMBOL_GPL(devm_mux_chip_register);

	/**
	* mux_control_states() - Query the number of multiplexer states.
	* @mux: The mux-control to query.
	*
	* Return: The number of multiplexer states.
	*/
	unsigned int mux_control_states(struct mux_control *mux)
	{
	return mux->states;
	}
	EXPORT_SYMBOL_GPL(mux_control_states);

	/*
	* The mux->lock must be down when calling this function.
	*/
	static int __mux_control_select(struct mux_control *mux, int state)
	{
	int ret;

	if (WARN_ON(state < 0 \|\| state >= mux->states))
	return -EINVAL;

	if (mux->cached_state == state)
	return 0;

	ret = mux_control_set(mux, state);
	if (ret >= 0)
	return 0;

	/* The mux update failed, try to revert if appropriate... */
	if (mux->idle_state != MUX_IDLE_AS_IS)
	mux_control_set(mux, mux->idle_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.
	*
	* On successfully selecting the mux-control state, it will be locked until
	* there is a call to mux_control_deselect(). If the mux-control is already
	* selected when mux_control_select() is called, the caller will be blocked
	* until mux_control_deselect() is called (by someone else).
	*
	* Therefore, 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.
	*
	* Return: 0 when the mux-control state has the requested state or a negative
	* errno on error.
	*/
	int mux_control_select(struct mux_control *mux, unsigned int state)
	{
	int ret;

	ret = down_killable(&mux->lock);
	if (ret < 0)
	return ret;

	ret = __mux_control_select(mux, state);

	if (ret < 0)
	up(&mux->lock);

	return ret;
	}
	EXPORT_SYMBOL_GPL(mux_control_select);

	/**
	* mux_control_try_select() - Try to select the given multiplexer state.
	* @mux: The mux-control to request a change of state from.
	* @state: The new requested state.
	*
	* On successfully selecting the mux-control state, it will be locked until
	* mux_control_deselect() called.
	*
	* Therefore, 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_try_select() fails.
	*
	* Return: 0 when the mux-control state has the requested state or a negative
	* errno on error. Specifically -EBUSY if the mux-control is contended.
	*/
	int mux_control_try_select(struct mux_control *mux, unsigned int state)
	{
	int ret;

	if (down_trylock(&mux->lock))
	return -EBUSY;

	ret = __mux_control_select(mux, state);

	if (ret < 0)
	up(&mux->lock);

	return ret;
	}
	EXPORT_SYMBOL_GPL(mux_control_try_select);

	/**
	* mux_control_deselect() - Deselect the previously selected multiplexer state.
	* @mux: The mux-control to deselect.
	*
	* It is required that a single call is made to mux_control_deselect() for
	* each and every successful call made to either of mux_control_select() or
	* mux_control_try_select().
	*
	* Return: 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 and is thus free for the next access.
	*/
	int mux_control_deselect(struct mux_control *mux)
	{
	int ret = 0;

	if (mux->idle_state != MUX_IDLE_AS_IS &&
	mux->idle_state != mux->cached_state)
	ret = mux_control_set(mux, mux->idle_state);

	up(&mux->lock);

	return ret;
	}
	EXPORT_SYMBOL_GPL(mux_control_deselect);

	/* Note this function returns a reference to the mux_chip dev. */
	static struct mux_chip of_find_mux_chip_by_node(struct device_node np)
	{
	struct device *dev;

	dev = class_find_device_by_of_node(&mux_class, np);

	return dev ? to_mux_chip(dev) : NULL;
	}

	/**
	* mux_control_get() - Get the mux-control for a device.
	* @dev: The device that needs a mux-control.
	* @mux_name: The name identifying the mux-control.
	*
	* Return: A pointer to the mux-control, or an ERR_PTR with a negative errno.
	*/
	struct mux_control mux_control_get(struct device dev, const char *mux_name)
	{
	struct device_node *np = dev->of_node;
	struct of_phandle_args args;
	struct mux_chip *mux_chip;
	unsigned int controller;
	int index = 0;
	int ret;

	if (mux_name) {
	index = of_property_match_string(np, "mux-control-names",
	mux_name);
	if (index < 0) {
	dev_err(dev, "mux controller '%s' not found\n",
	mux_name);
	return ERR_PTR(index);
	}
	}

	ret = of_parse_phandle_with_args(np,
	"mux-controls", "#mux-control-cells",
	index, &args);
	if (ret) {
	dev_err(dev, "%pOF: failed to get mux-control %s(%i)\n",
	np, mux_name ?: "", index);
	return ERR_PTR(ret);
	}

	mux_chip = of_find_mux_chip_by_node(args.np);
	of_node_put(args.np);
	if (!mux_chip)
	return ERR_PTR(-EPROBE_DEFER);

	if (args.args_count > 1 \|\|
	(!args.args_count && (mux_chip->controllers > 1))) {
	dev_err(dev, "%pOF: wrong #mux-control-cells for %pOF\n",
	np, args.np);
	put_device(&mux_chip->dev);
	return ERR_PTR(-EINVAL);
	}

	controller = 0;
	if (args.args_count)
	controller = args.args[0];

	if (controller >= mux_chip->controllers) {
	dev_err(dev, "%pOF: bad mux controller %u specified in %pOF\n",
	np, controller, args.np);
	put_device(&mux_chip->dev);
	return ERR_PTR(-EINVAL);
	}

	return &mux_chip->mux[controller];
	}
	EXPORT_SYMBOL_GPL(mux_control_get);

	/**
	* mux_control_put() - Put away the mux-control for good.
	* @mux: The mux-control to put away.
	*
	* mux_control_put() reverses the effects of mux_control_get().
	*/
	void mux_control_put(struct mux_control *mux)
	{
	put_device(&mux->chip->dev);
	}
	EXPORT_SYMBOL_GPL(mux_control_put);

	static void devm_mux_control_release(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.
	* @mux_name: The name identifying the mux-control.
	*
	* Return: Pointer to the mux-control, or an ERR_PTR with a negative errno.
	*/
	struct mux_control devm_mux_control_get(struct device dev,
	const char *mux_name)
	{
	struct mux_control *ptr, mux;

	ptr = devres_alloc(devm_mux_control_release, sizeof(*ptr), GFP_KERNEL);
	if (!ptr)
	return ERR_PTR(-ENOMEM);

	mux = mux_control_get(dev, mux_name);
	if (IS_ERR(mux)) {
	devres_free(ptr);
	return mux;
	}

	*ptr = mux;
	devres_add(dev, ptr);

	return mux;
	}
	EXPORT_SYMBOL_GPL(devm_mux_control_get);

	/*
	* Using subsys_initcall instead of module_init here to try to ensure - for
	* the non-modular case - that the subsystem is initialized when mux consumers
	* and mux controllers start to use it.
	* For the modular case, the ordering is ensured with module dependencies.
	*/
	subsys_initcall(mux_init);
	module_exit(mux_exit);

	MODULE_DESCRIPTION("Multiplexer subsystem");
	MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
	MODULE_LICENSE("GPL v2");