Re: [RFC PATCH v2 2/7] misc: minimal mux subsystem and gpio-based mux controller

[Peter Rosin <peda@axentia.se>]

On 2016-11-19 16:34, Jonathan Cameron wrote:
> 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.

I'll make it more general for the next round.

> 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.

I think that can be easily added later, when/if it's needed.

>>
>> 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.

Right, I'll leave it for later when/if it's needed.

>> +	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?

Good suggestion, I'll add an inline function and drop the priv member.

>> +
>> +	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...

Kernel doc was the plan from the start, coming up...

>> + */
>> +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)

Right, now that you mention it, I remember having seen that document
at some point. I'll look it up.

Thanks for all comments!

Cheers,
Peter

>> +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@axentia.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@axentia.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 */
>>
>