Date:   Sun, 8 Jan 2017 10:23:31 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Peter Rosin <peda@...ntia.se>, linux-kernel@...r.kernel.org
Cc:     Wolfram Sang <wsa@...-dreams.de>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Jonathan Corbet <corbet@....net>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-iio@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v7 03/12] mux: minimal mux subsystem and gpio-based mux
 controller

On 04/01/17 12:16, Peter Rosin wrote:
> Add a new minimalistic subsystem that handles multiplexer controllers.
> When multiplexers are used in various places in the kernel, and the
> same multiplexer controller can be used for several independent things,
> there should be one place to implement support for said multiplexer
> controller.
> 
> A single multiplexer controller can also be used to control several
> parallel multiplexers, that are in turn used by different subsystems
> in the kernel, leading to a need to coordinate multiplexer accesses.
> The multiplexer subsystem handles this coordination.
> 
> This new mux controller subsystem initially comes with a single backend
> driver that controls gpio based multiplexers. Even though not needed by
> this initial driver, the mux controller subsystem is prepared to handle
> chips with multiple (independent) mux controllers.
> 
> Signed-off-by: Peter Rosin <peda@...ntia.se>
Reviewed-by: Jonathan Cameron <jic23@...nel.org>
> ---
>  Documentation/driver-model/devres.txt |   8 +
>  MAINTAINERS                           |   2 +
>  drivers/Kconfig                       |   2 +
>  drivers/Makefile                      |   1 +
>  drivers/mux/Kconfig                   |  33 +++
>  drivers/mux/Makefile                  |   6 +
>  drivers/mux/mux-core.c                | 398 ++++++++++++++++++++++++++++++++++
>  drivers/mux/mux-gpio.c                | 120 ++++++++++
>  include/linux/mux.h                   | 244 +++++++++++++++++++++
>  9 files changed, 814 insertions(+)
>  create mode 100644 drivers/mux/Kconfig
>  create mode 100644 drivers/mux/Makefile
>  create mode 100644 drivers/mux/mux-core.c
>  create mode 100644 drivers/mux/mux-gpio.c
>  create mode 100644 include/linux/mux.h
> 
> diff --git a/Documentation/driver-model/devres.txt b/Documentation/driver-model/devres.txt
> index dc51fb024190..1e9ae701a587 100644
> --- a/Documentation/driver-model/devres.txt
> +++ b/Documentation/driver-model/devres.txt
> @@ -332,6 +332,14 @@ MEM
>  MFD
>    devm_mfd_add_devices()
>  
> +MUX
> +  devm_mux_chip_alloc()
> +  devm_mux_chip_free()
> +  devm_mux_chip_register()
> +  devm_mux_chip_unregister()
> +  devm_mux_control_get()
> +  devm_mux_control_put()
> +
>  PER-CPU MEM
>    devm_alloc_percpu()
>    devm_free_percpu()
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 32abef2b6d05..ebe96f3e25a0 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8442,6 +8442,8 @@ MULTIPLEXER SUBSYSTEM
>  M:	Peter Rosin <peda@...ntia.se>
>  S:	Maintained
>  F:	Documentation/devicetree/bindings/mux/
> +F:	include/linux/mux.h
> +F:	drivers/mux/
>  
>  MULTISOUND SOUND DRIVER
>  M:	Andrew Veliath <andrewtv@....net>
> diff --git a/drivers/Kconfig b/drivers/Kconfig
> index e1e2066cecdb..993aeb65affa 100644
> --- a/drivers/Kconfig
> +++ b/drivers/Kconfig
> @@ -76,6 +76,8 @@ source "drivers/hwmon/Kconfig"
>  
>  source "drivers/thermal/Kconfig"
>  
> +source "drivers/mux/Kconfig"
> +

Why this location in the list?  I think the convention for new subystems is
to just go last in the list.

>  source "drivers/watchdog/Kconfig"
>  
>  source "drivers/ssb/Kconfig"
> diff --git a/drivers/Makefile b/drivers/Makefile
> index 060026a02f59..d089baa57965 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -112,6 +112,7 @@ obj-$(CONFIG_W1)		+= w1/
>  obj-y				+= power/
>  obj-$(CONFIG_HWMON)		+= hwmon/
>  obj-$(CONFIG_THERMAL)		+= thermal/
> +obj-$(CONFIG_MULTIPLEXER)	+= mux/
>  obj-$(CONFIG_WATCHDOG)		+= watchdog/
>  obj-$(CONFIG_MD)		+= md/
>  obj-$(CONFIG_BT)		+= bluetooth/
> diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
> new file mode 100644
> index 000000000000..de5a35ffe7af
> --- /dev/null
> +++ b/drivers/mux/Kconfig
> @@ -0,0 +1,33 @@
> +#
> +# Multiplexer devices
> +#
> +
> +menuconfig MULTIPLEXER
> +	bool "Multiplexer subsystem"
> +	help
> +	  Multiplexer controller subsystem. Multiplexers are used in a
> +	  variety of settings, and this subsystem abstracts their use
> +	  so that the rest of the kernel sees a common interface. When
> +	  multiple parallel multiplexers are controlled by one single
> +	  multiplexer controller, this subsystem also coordinates the
> +	  multiplexer accesses.
> +
> +	  If unsure, say no.
> +
> +if MULTIPLEXER
> +
> +config MUX_GPIO
> +	tristate "GPIO-controlled Multiplexer"
> +	depends on OF && GPIOLIB
> +	help
> +	  GPIO-controlled Multiplexer controller.
> +
> +	  The driver builds a single multiplexer controller using a number
> +	  of gpio pins. For N pins, there will be 2^N possible multiplexer
> +	  states. The GPIO pins can be connected (by the hardware) to several
> +	  multiplexers, which in that case will be operated in parallel.
> +
> +	  To compile this driver as a module, choose M here: the module will
> +	  be called mux-gpio.
> +
> +endif
> diff --git a/drivers/mux/Makefile b/drivers/mux/Makefile
> new file mode 100644
> index 000000000000..facc43da3648
> --- /dev/null
> +++ b/drivers/mux/Makefile
> @@ -0,0 +1,6 @@
> +#
> +# Makefile for multiplexer devices.
> +#
> +
> +obj-$(CONFIG_MULTIPLEXER)      	+= mux-core.o
> +obj-$(CONFIG_MUX_GPIO)		+= mux-gpio.o
> diff --git a/drivers/mux/mux-core.c b/drivers/mux/mux-core.c
> new file mode 100644
> index 000000000000..21da15a264ad
> --- /dev/null
> +++ b/drivers/mux/mux-core.c
> @@ -0,0 +1,398 @@
> +/*
> + * Multiplexer subsystem
> + *
> + * Copyright (C) 2016 Axentia Technologies AB
> + *
> + * Author: Peter Rosin <peda@...ntia.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.
> + */
> +
> +#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 class mux_class = {
> +	.name = "mux",
> +	.owner = THIS_MODULE,
> +};
> +
> +static int __init mux_init(void)
> +{
> +	return class_register(&mux_class);
> +}
> +
> +static DEFINE_IDA(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 struct device_type mux_type = {
> +	.name = "mux-chip",
> +	.release = mux_chip_release,
> +};
> +
> +struct mux_chip *mux_chip_alloc(struct device *dev,
> +				unsigned int controllers, size_t sizeof_priv)
> +{
> +	struct mux_chip *mux_chip;
> +	int i;
> +
> +	if (!dev || !controllers)
> +		return NULL;
> +
> +	mux_chip = kzalloc(sizeof(*mux_chip) +
> +			   controllers * sizeof(*mux_chip->mux) +
> +			   sizeof_priv, GFP_KERNEL);
> +	if (!mux_chip)
> +		return NULL;
> +
> +	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) {
> +		pr_err("muxchipX failed to get a device id\n");
> +		kfree(mux_chip);
> +		return NULL;
> +	}
> +	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;
> +		init_rwsem(&mux->lock);
> +		mux->cached_state = -1;
> +		mux->idle_state = -1;
> +	}
> +
> +	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 ? -1 : state;
> +
> +	return ret;
> +}
> +
> +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)
> +			return ret;
> +	}
> +
> +	return device_add(&mux_chip->dev);
> +}
> +EXPORT_SYMBOL_GPL(mux_chip_register);
> +
> +void mux_chip_unregister(struct mux_chip *mux_chip)
> +{
> +	device_del(&mux_chip->dev);
> +}
> +EXPORT_SYMBOL_GPL(mux_chip_unregister);
> +
> +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);
> +}
> +
> +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 int devm_mux_chip_match(struct device *dev, void *res, void *data)
> +{
> +	struct mux_chip **r = res;
> +
> +	if (!r || !*r) {
> +		WARN_ON(!r || !*r);
> +		return 0;
> +	}
> +
> +	return *r == data;
> +}
> +
> +void devm_mux_chip_free(struct device *dev, struct mux_chip *mux_chip)
> +{
> +	WARN_ON(devres_release(dev, devm_mux_chip_release,
> +			       devm_mux_chip_match, mux_chip));
> +}
> +EXPORT_SYMBOL_GPL(devm_mux_chip_free);
> +
> +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);
> +}
> +
> +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);
> +
> +void devm_mux_chip_unregister(struct device *dev, struct mux_chip *mux_chip)
> +{
> +	WARN_ON(devres_release(dev, devm_mux_chip_reg_release,
> +			       devm_mux_chip_match, mux_chip));
> +}
> +EXPORT_SYMBOL_GPL(devm_mux_chip_unregister);
> +
> +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);
> +
> +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, const void *data)
> +{
> +	return dev->of_node == data;
> +}
> +
> +static struct mux_chip *of_find_mux_chip_by_node(struct device_node *np)
> +{
> +	struct device *dev;
> +
> +	dev = class_find_device(&mux_class, NULL, np, of_dev_node_match);
> +
> +	return dev ? to_mux_chip(dev) : NULL;
> +}
> +
> +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)
> +			return ERR_PTR(index);
> +	}
> +
> +	ret = of_parse_phandle_with_args(np,
> +					 "mux-controls", "#mux-control-cells",
> +					 index, &args);
> +	if (ret) {
> +		dev_err(dev, "%s: failed to get mux-control %s(%i)\n",
> +			np->full_name, 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, "%s: wrong #mux-control-cells for %s\n",
> +			np->full_name, args.np->full_name);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	controller = 0;
> +	if (args.args_count)
> +		controller = args.args[0];
> +
> +	if (controller >= mux_chip->controllers)
> +		return ERR_PTR(-EINVAL);
> +
> +	get_device(&mux_chip->dev);
> +	return &mux_chip->mux[controller];
> +}
> +EXPORT_SYMBOL_GPL(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);
> +}
> +
> +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);
> +
> +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;
> +}
> +
> +void devm_mux_control_put(struct device *dev, struct mux_control *mux)
> +{
> +	WARN_ON(devres_release(dev, devm_mux_control_release,
> +			       devm_mux_control_match, mux));
> +}
> +EXPORT_SYMBOL_GPL(devm_mux_control_put);
> +
> +subsys_initcall(mux_init);
> +
> +MODULE_DESCRIPTION("Multiplexer subsystem");
> +MODULE_AUTHOR("Peter Rosin <peda@...ntia.se");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/mux/mux-gpio.c b/drivers/mux/mux-gpio.c
> new file mode 100644
> index 000000000000..76b52bc63470
> --- /dev/null
> +++ b/drivers/mux/mux-gpio.c
> @@ -0,0 +1,120 @@
> +/*
> + * GPIO-controlled multiplexer driver
> + *
> + * Copyright (C) 2016 Axentia Technologies AB
> + *
> + * Author: Peter Rosin <peda@...ntia.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/gpio/consumer.h>
> +#include <linux/module.h>
> +#include <linux/mux.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +
> +struct mux_gpio {
> +	struct gpio_descs *gpios;
> +	int *val;
> +};
> +
> +static int mux_gpio_set(struct mux_control *mux, int state)
> +{
> +	struct mux_gpio *mux_gpio = mux_chip_priv(mux->chip);
> +	int i;
> +
> +	for (i = 0; i < mux_gpio->gpios->ndescs; i++)
> +		mux_gpio->val[i] = (state >> i) & 1;
> +
> +	gpiod_set_array_value_cansleep(mux_gpio->gpios->ndescs,
> +				       mux_gpio->gpios->desc,
> +				       mux_gpio->val);
> +
> +	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 = dev->of_node;
> +	struct mux_chip *mux_chip;
> +	struct mux_gpio *mux_gpio;
> +	int pins;
> +	u32 idle_state;
> +	int ret;
> +
> +	if (!np)
> +		return -ENODEV;
> +
> +	pins = gpiod_count(dev, "mux");
> +	if (pins < 0)
> +		return pins;
> +
> +	mux_chip = devm_mux_chip_alloc(dev, 1, sizeof(*mux_gpio) +
> +				       pins * sizeof(*mux_gpio->val));
> +	if (!mux_chip)
> +		return -ENOMEM;
> +
> +	mux_gpio = mux_chip_priv(mux_chip);
> +	mux_gpio->val = (int *)(mux_gpio + 1);
> +	mux_chip->ops = &mux_gpio_ops;
> +
> +	mux_gpio->gpios = devm_gpiod_get_array(dev, "mux", GPIOD_OUT_LOW);
> +	if (IS_ERR(mux_gpio->gpios)) {
> +		ret = PTR_ERR(mux_gpio->gpios);
> +		if (ret != -EPROBE_DEFER)
> +			dev_err(dev, "failed to get gpios\n");
> +		return ret;
> +	}
> +	WARN_ON(pins != mux_gpio->gpios->ndescs);
> +	mux_chip->mux->states = 1 << pins;
> +
> +	ret = device_property_read_u32(dev, "idle-state", &idle_state);
> +	if (ret >= 0) {
> +		if (idle_state >= mux_chip->mux->states) {
> +			dev_err(dev, "invalid idle-state %u\n", idle_state);
> +			return -EINVAL;
> +		}
> +
> +		mux_chip->mux->idle_state = idle_state;
> +	}
> +
> +	ret = devm_mux_chip_register(dev, mux_chip);
> +	if (ret < 0) {
> +		dev_err(dev, "failed to register mux-chip\n");
> +		return ret;
> +	}
> +
> +	dev_info(dev, "%u-way mux-controller registered\n",
> +		 mux_chip->mux->states);
> +
> +	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,
> +};
> +module_platform_driver(mux_gpio_driver);
> +
> +MODULE_DESCRIPTION("GPIO-controlled multiplexer driver");
> +MODULE_AUTHOR("Peter Rosin <peda@...ntia.se");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/mux.h b/include/linux/mux.h
> new file mode 100644
> index 000000000000..3b9439927f11
> --- /dev/null
> +++ b/include/linux/mux.h
> @@ -0,0 +1,244 @@
> +/*
> + * mux.h - definitions for the multiplexer interface
> + *
> + * Copyright (C) 2016 Axentia Technologies AB
> + *
> + * Author: Peter Rosin <peda@...ntia.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.
> + */
> +
> +#ifndef _LINUX_MUX_H
> +#define _LINUX_MUX_H
> +
> +#include <linux/device.h>
> +#include <linux/rwsem.h>
> +
> +struct mux_chip;
> +struct mux_control;
> +struct platform_device;
> +
> +struct mux_control_ops {
> +	int (*set)(struct mux_control *mux, int state);
> +};
> +
> +/**
> + * struct mux_control - Represents a mux controller.
> + * @lock:		Protects the mux controller state.
> + * @chip:		The mux chip that is handling this mux controller.
> + * @states:		The number of mux controller states.
> + * @cached_state:	The current mux controller state, or -1 if none.
> + * @idle_state:		The mux controller state to use when inactive, or -1
> + *			for none.
> + */
> +struct mux_control {
> +	struct rw_semaphore lock; /* protects the state of the mux */
> +
> +	struct mux_chip *chip;
> +
> +	unsigned int states;
> +	int cached_state;
> +	int idle_state;
> +};
> +
> +/**
> + * struct mux_chip -	Represents a chip holding mux controllers.
> + * @controllers:	Number of mux controllers handled by the chip.
> + * @mux:		Array of mux controllers that is handled.
> + * @dev:		Device structure.
> + * @id:			Used to identify the device internally.
> + * @ops:		Mux controller operations.
> + */
> +struct mux_chip {
> +	unsigned int controllers;
> +	struct mux_control *mux;
> +	struct device dev;
> +	int id;
> +
> +	const struct mux_control_ops *ops;
> +};
> +
> +#define to_mux_chip(x) container_of((x), struct mux_chip, dev)
> +
> +/**
> + * mux_chip_priv() - Get the extra memory reserved by mux_chip_alloc().
> + * @mux_chip: The mux-chip to get the private memory from.
> + *
> + * Return: Pointer to the private memory reserved by the allocator.
> + */
> +static inline void *mux_chip_priv(struct mux_chip *mux_chip)
> +{
> +	return &mux_chip->mux[mux_chip->controllers];
> +}
> +
> +/**
> + * 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.
> + *
> + * Return: A pointer to the new mux-chip, NULL on failure.
> + */
> +struct mux_chip *mux_chip_alloc(struct device *dev,
> +				unsigned int controllers, size_t sizeof_priv);
> +
> +/**
> + * 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);
> +
> +/**
> + * 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);
> +
> +/**
> + * 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);
> +
> +/**
> + * 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, NULL on failure.
> + */
> +struct mux_chip *devm_mux_chip_alloc(struct device *dev,
> +				     unsigned int controllers,
> +				     size_t sizeof_priv);
> +
> +/**
> + * 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);
> +
> +/**
> + * devm_mux_chip_unregister() - Resource-managed version mux_chip_unregister().
> + * @dev: The device that originally registered the mux-chip.
> + * @mux_chip: The mux-chip to unregister.
> + *
> + * See mux_chip_unregister() for more details.
> + *
> + * Note that you do not normally need to call this function.
> + */
> +void devm_mux_chip_unregister(struct device *dev, struct mux_chip *mux_chip);
> +
> +/**
> + * devm_mux_chip_free() - Resource-managed version mux_chip_free().
> + * @dev: The device that originally got the mux-chip.
> + * @mux_chip: The mux-chip to free.
> + *
> + * See mux_chip_free() for more details.
> + *
> + * Note that you do not normally need to call this function.
> + */
> +void devm_mux_chip_free(struct device *dev, struct mux_chip *mux_chip);
> +
> +/**
> + * mux_control_select() - Select the given multiplexer state.
> + * @mux: The mux-control to request a change of state from.
> + * @state: The new requested state.
> + *
> + * 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 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 perhaps not be making
> + * assumptions about.
> + */
> +int mux_control_select(struct mux_control *mux, int state);
> +
> +/**
> + * mux_control_deselect() - Deselect the previously selected multiplexer state.
> + * @mux: The mux-control to deselect.
> + *
> + * 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 for others to access.
> + */
> +int mux_control_deselect(struct mux_control *mux);
> +
> +/**
> + * mux_control_get_index() - Get the index of the given mux controller
> + * @mux: The mux-control to the the index for.
> + *
> + * Return: The index of the mux controller within the mux chip the mux
> + * controller is a part of.
> + */
> +static inline unsigned int mux_control_get_index(struct mux_control *mux)
> +{
> +	return mux - mux->chip->mux;
> +}
> +
> +/**
> + * 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);
> +
> +/**
> + * 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);
> +
> +/**
> + * 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);
> +
> +/**
> + * 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);
> +
> +#endif /* _LINUX_MUX_H */
> 

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