Date:   Sat, 19 Nov 2016 15:34:42 +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>,
        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
Subject: Re: [RFC PATCH v2 2/7] misc: minimal mux subsystem and gpio-based mux
 controller

On 17/11/16 21:48, Peter Rosin wrote:
> When both the iio subsystem and the i2c subsystem wants to update
> the same mux, there needs to be some coordination. Invent a new
> minimal "mux" subsystem that handles this.
I'd probably put something more general in the description. Lots of things
may need the same infrastructure.  This is just an example.

Few bits inline.

Also, I suspect you will fairly rapidly have a need for a strobe signal
as well.  A lot of mux chips that are more than 2 way seem to have them to
allow multiple chips to be synchronized.
> 
> Add a single backend driver for this new subsystem that can
> control gpio based multiplexers.
> ---
>  drivers/misc/Kconfig    |   6 +
>  drivers/misc/Makefile   |   2 +
>  drivers/misc/mux-core.c | 299 ++++++++++++++++++++++++++++++++++++++++++++++++
>  drivers/misc/mux-gpio.c | 115 +++++++++++++++++++
>  include/linux/mux.h     |  53 +++++++++
>  5 files changed, 475 insertions(+)
>  create mode 100644 drivers/misc/mux-core.c
>  create mode 100644 drivers/misc/mux-gpio.c
>  create mode 100644 include/linux/mux.h
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 64971baf11fa..9e119bb78d82 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -766,6 +766,12 @@ 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 MUX_GPIO
> +	tristate "GPIO-controlled MUX controller"
> +	depends on OF
> +	help
> +	  GPIO-controlled MUX controller
> +
>  source "drivers/misc/c2port/Kconfig"
>  source "drivers/misc/eeprom/Kconfig"
>  source "drivers/misc/cb710/Kconfig"
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index 31983366090a..92b547bcbac1 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -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-$(CONFIG_MUX_GPIO)          += mux-core.o
> +obj-$(CONFIG_MUX_GPIO)          += mux-gpio.o
>  
>  lkdtm-$(CONFIG_LKDTM)		+= lkdtm_core.o
>  lkdtm-$(CONFIG_LKDTM)		+= lkdtm_bugs.o
> diff --git a/drivers/misc/mux-core.c b/drivers/misc/mux-core.c
> new file mode 100644
> index 000000000000..7a8bf003a92c
> --- /dev/null
> +++ b/drivers/misc/mux-core.c
> @@ -0,0 +1,299 @@
> +/*
> + * 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/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,
> +};
> +
> +/*
> + * Allocate a mux-control, plus an extra memory area for private use
> + * by the caller.
> + */
> +struct mux_control *mux_control_alloc(size_t sizeof_priv)
> +{
> +	struct mux_control *mux;
> +
Worth planning ahead for spi controlled muxes and others that need their
structures to be carefully aligned to avoid dma cacheline fun?
Easy enough to add later I guess.
> +	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->priv = mux + 1;
Needed?  Or just do it with a bit of pointer math where the access is needed?
> +
> +	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);
> +
> +/*
> + * Register the mux-control, thus readying it for use.
Either single line comment style - or perhaps kernel doc the lot...
> + */
> +int mux_control_register(struct mux_control *mux)
> +{
> +	/* 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;
> +
> +	return device_add(&mux->dev);
> +}
> +EXPORT_SYMBOL_GPL(mux_control_register);
> +
> +/*
> + * Take the mux-control off-line.
> + */
> +void mux_control_unregister(struct mux_control *mux)
> +{
> +	device_del(&mux->dev);
> +}
> +EXPORT_SYMBOL_GPL(mux_control_unregister);
> +
> +/*
> + * Put away the mux-control for good.
> + */
> +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;
> +}
> +
> +/*
> + * Select the given multiplexer channel. Call mux_control_deselect()
> + * when the operation is complete on the multiplexer channel, and the
> + * multiplexer is free for others to use.
> + */
> +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);
> +
> +/*
> + * Deselect the previously selected multiplexer channel.
> + */
> +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;
> +}
> +
> +static struct mux_control *of_mux_control_get(struct device_node *np, int index)
> +{
> +	struct device_node *mux_np;
> +	struct mux_control *mux;
> +
> +	mux_np = of_parse_phandle(np, "control-muxes", index);
> +	if (!mux_np)
> +		return NULL;
> +
> +	mux = of_find_mux_by_node(mux_np);
> +	of_node_put(mux_np);
> +
> +	return mux;
> +}
> +
> +/*
> + * Get a named mux.
> + */
> +struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
> +{
> +	struct device_node *np = dev->of_node;
> +	struct mux_control *mux;
> +	int index;
> +
> +	index = of_property_match_string(np, "control-mux-names", mux_name);
> +	if (index < 0) {
> +		dev_err(dev, "failed to get control-mux %s:%s(%i)\n",
> +			np->full_name, mux_name ?: "", index);
> +		return ERR_PTR(index);
> +	}
> +
> +	mux = of_mux_control_get(np, index);
> +	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);
> +}
> +
> +/*
> + * Get a named mux, with resource management.
> + */
Guess it might be elsewhere in patch set but remember to add this to
the global list of devm interfaces (in Documentation somewhere.. IIRC)
> +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_free, 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;
> +}
> +
> +/*
> + * Resource-managed version mux_control_put.
> + */
> +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@...ntia.se");
> +MODULE_DESCRIPTION("MUX subsystem");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/misc/mux-gpio.c b/drivers/misc/mux-gpio.c
> new file mode 100644
> index 000000000000..2ddd7fb24078
> --- /dev/null
> +++ b/drivers/misc/mux-gpio.c
> @@ -0,0 +1,115 @@
> +/*
> + * 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->priv;
> +	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->priv;
> +	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);
> +	}
> +
> +	ret = of_property_read_u32(np, "idle-state", &idle_state);
> +	if (ret >= 0) {
> +		if (idle_state >= (1 << mux_gpio->gpios->ndescs)) {
> +			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@...ntia.se");
> +MODULE_DESCRIPTION("GPIO-controlled multiplexer driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/mux.h b/include/linux/mux.h
> new file mode 100644
> index 000000000000..5b21b8184056
> --- /dev/null
> +++ b/include/linux/mux.h
> @@ -0,0 +1,53 @@
> +/*
> + * 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;
> +
> +	int cached_state;
> +	int idle_state;
> +
> +	const struct mux_control_ops *ops;
> +
> +	void *priv;
> +};
> +
> +#define to_mux_control(x) container_of((x), struct mux_control, dev)
> +
> +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,
> +				    const char *mux_name);
> +struct mux_control *devm_mux_control_get(struct device *dev,
> +					 const char *mux_name);
> +void devm_mux_control_put(struct device *dev, struct mux_control *mux);
> +
> +#endif /* _LINUX_MUX_H */
> 

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