xref: /linux/drivers/power/sequencing/core.c (revision a1ff5a7d78a036d6c2178ee5acd6ba4946243800)

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2024 Linaro Ltd.
 */

#include <linux/bug.h>
#include <linux/cleanup.h>
#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/export.h>
#include <linux/idr.h>
#include <linux/kernel.h>
#include <linux/kref.h>
#include <linux/list.h>
#include <linux/lockdep.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/property.h>
#include <linux/pwrseq/consumer.h>
#include <linux/pwrseq/provider.h>
#include <linux/radix-tree.h>
#include <linux/rwsem.h>
#include <linux/slab.h>

/*
 * Power-sequencing framework for linux.
 *
 * This subsystem allows power sequence providers to register a set of targets
 * that consumers may request and power-up/down.
 *
 * Glossary:
 *
 * Unit - a unit is a discreet chunk of a power sequence. For instance one unit
 * may enable a set of regulators, another may enable a specific GPIO. Units
 * can define dependencies in the form of other units that must be enabled
 * before it itself can be.
 *
 * Target - a target is a set of units (composed of the "final" unit and its
 * dependencies) that a consumer selects by its name when requesting a handle
 * to the power sequencer. Via the dependency system, multiple targets may
 * share the same parts of a power sequence but ignore parts that are
 * irrelevant.
 *
 * Descriptor - a handle passed by the pwrseq core to every consumer that
 * serves as the entry point to the provider layer. It ensures coherence
 * between different users and keeps reference counting consistent.
 *
 * Each provider must define a .match() callback whose role is to determine
 * whether a potential consumer is in fact associated with this sequencer.
 * This allows creating abstraction layers on top of regular device-tree
 * resources like regulators, clocks and other nodes connected to the consumer
 * via phandle.
 */

static DEFINE_IDA(pwrseq_ida);

/*
 * Protects the device list on the pwrseq bus from concurrent modifications
 * but allows simultaneous read-only access.
 */
static DECLARE_RWSEM(pwrseq_sem);

/**
 * struct pwrseq_unit - Private power-sequence unit data.
 * @ref: Reference count for this object. When it goes to 0, the object is
 *       destroyed.
 * @name: Name of this target.
 * @list: Link to siblings on the list of all units of a single sequencer.
 * @deps: List of units on which this unit depends.
 * @enable: Callback running the part of the power-on sequence provided by
 *          this unit.
 * @disable: Callback running the part of the power-off sequence provided
 *           by this unit.
 * @enable_count: Current number of users that enabled this unit. May be the
 *                consumer of the power sequencer or other units that depend
 *                on this one.
 */
struct pwrseq_unit {
	struct kref ref;
	const char *name;
	struct list_head list;
	struct list_head deps;
	pwrseq_power_state_func enable;
	pwrseq_power_state_func disable;
	unsigned int enable_count;
};

static struct pwrseq_unit *pwrseq_unit_new(const struct pwrseq_unit_data *data)
{
	struct pwrseq_unit *unit;

	unit = kzalloc(sizeof(*unit), GFP_KERNEL);
	if (!unit)
		return NULL;

	unit->name = kstrdup_const(data->name, GFP_KERNEL);
	if (!unit->name) {
		kfree(unit);
		return NULL;
	}

	kref_init(&unit->ref);
	INIT_LIST_HEAD(&unit->deps);
	unit->enable = data->enable;
	unit->disable = data->disable;

	return unit;
}

static struct pwrseq_unit *pwrseq_unit_get(struct pwrseq_unit *unit)
{
	kref_get(&unit->ref);

	return unit;
}

static void pwrseq_unit_release(struct kref *ref);

static void pwrseq_unit_put(struct pwrseq_unit *unit)
{
	kref_put(&unit->ref, pwrseq_unit_release);
}

/**
 * struct pwrseq_unit_dep - Wrapper around a reference to the unit structure
 *                          allowing to keep it on multiple dependency lists
 *                          in different units.
 * @list: Siblings on the list.
 * @unit: Address of the referenced unit.
 */
struct pwrseq_unit_dep {
	struct list_head list;
	struct pwrseq_unit *unit;
};

static struct pwrseq_unit_dep *pwrseq_unit_dep_new(struct pwrseq_unit *unit)
{
	struct pwrseq_unit_dep *dep;

	dep = kzalloc(sizeof(*dep), GFP_KERNEL);
	if (!dep)
		return NULL;

	dep->unit = unit;

	return dep;
}

static void pwrseq_unit_dep_free(struct pwrseq_unit_dep *ref)
{
	pwrseq_unit_put(ref->unit);
	kfree(ref);
}

static void pwrseq_unit_free_deps(struct list_head *list)
{
	struct pwrseq_unit_dep *dep, *next;

	list_for_each_entry_safe(dep, next, list, list) {
		list_del(&dep->list);
		pwrseq_unit_dep_free(dep);
	}
}

static void pwrseq_unit_release(struct kref *ref)
{
	struct pwrseq_unit *unit = container_of(ref, struct pwrseq_unit, ref);

	pwrseq_unit_free_deps(&unit->deps);
	list_del(&unit->list);
	kfree_const(unit->name);
	kfree(unit);
}

/**
 * struct pwrseq_target - Private power-sequence target data.
 * @list: Siblings on the list of all targets exposed by a power sequencer.
 * @name: Name of the target.
 * @unit: Final unit for this target.
 * @post_enable: Callback run after the target unit has been enabled, *after*
 *               the state lock has been released. It's useful for implementing
 *               boot-up delays without blocking other users from powering up
 *               using the same power sequencer.
 */
struct pwrseq_target {
	struct list_head list;
	const char *name;
	struct pwrseq_unit *unit;
	pwrseq_power_state_func post_enable;
};

static struct pwrseq_target *
pwrseq_target_new(const struct pwrseq_target_data *data)
{
	struct pwrseq_target *target;

	target = kzalloc(sizeof(*target), GFP_KERNEL);
	if (!target)
		return NULL;

	target->name = kstrdup_const(data->name, GFP_KERNEL);
	if (!target->name) {
		kfree(target);
		return NULL;
	}

	target->post_enable = data->post_enable;

	return target;
}

static void pwrseq_target_free(struct pwrseq_target *target)
{
	if (!IS_ERR_OR_NULL(target->unit))
		pwrseq_unit_put(target->unit);
	kfree_const(target->name);
	kfree(target);
}

/**
 * struct pwrseq_device - Private power sequencing data.
 * @dev: Device struct associated with this sequencer.
 * @id: Device ID.
 * @owner: Prevents removal of active power sequencing providers.
 * @rw_lock: Protects the device from being unregistered while in use.
 * @state_lock: Prevents multiple users running the power sequence at the same
 *              time.
 * @match: Power sequencer matching callback.
 * @targets: List of targets exposed by this sequencer.
 * @units: List of all units supported by this sequencer.
 */
struct pwrseq_device {
	struct device dev;
	int id;
	struct module *owner;
	struct rw_semaphore rw_lock;
	struct mutex state_lock;
	pwrseq_match_func match;
	struct list_head targets;
	struct list_head units;
};

static struct pwrseq_device *to_pwrseq_device(struct device *dev)
{
	return container_of(dev, struct pwrseq_device, dev);
}

static struct pwrseq_device *pwrseq_device_get(struct pwrseq_device *pwrseq)
{
	get_device(&pwrseq->dev);

	return pwrseq;
}

static void pwrseq_device_put(struct pwrseq_device *pwrseq)
{
	put_device(&pwrseq->dev);
}

/**
 * struct pwrseq_desc - Wraps access to the pwrseq_device and ensures that one
 *                      user cannot break the reference counting for others.
 * @pwrseq: Reference to the power sequencing device.
 * @target: Reference to the target this descriptor allows to control.
 * @powered_on: Power state set by the holder of the descriptor (not necessarily
 * corresponding to the actual power state of the device).
 */
struct pwrseq_desc {
	struct pwrseq_device *pwrseq;
	struct pwrseq_target *target;
	bool powered_on;
};

static const struct bus_type pwrseq_bus = {
	.name = "pwrseq",
};

static void pwrseq_release(struct device *dev)
{
	struct pwrseq_device *pwrseq = to_pwrseq_device(dev);
	struct pwrseq_target *target, *pos;

	list_for_each_entry_safe(target, pos, &pwrseq->targets, list) {
		list_del(&target->list);
		pwrseq_target_free(target);
	}

	mutex_destroy(&pwrseq->state_lock);
	ida_free(&pwrseq_ida, pwrseq->id);
	kfree(pwrseq);
}

static const struct device_type pwrseq_device_type = {
	.name = "power_sequencer",
	.release = pwrseq_release,
};

static int pwrseq_check_unit_deps(const struct pwrseq_unit_data *data,
				  struct radix_tree_root *visited_units)
{
	const struct pwrseq_unit_data *tmp, **cur;
	int ret;

	ret = radix_tree_insert(visited_units, (unsigned long)data,
				(void *)data);
	if (ret)
		return ret;

	for (cur = data->deps; cur && *cur; cur++) {
		tmp = radix_tree_lookup(visited_units, (unsigned long)*cur);
		if (tmp) {
			WARN(1, "Circular dependency in power sequencing flow detected!\n");
			return -EINVAL;
		}

		ret = pwrseq_check_unit_deps(*cur, visited_units);
		if (ret)
			return ret;
	}

	return 0;
}

static int pwrseq_check_target_deps(const struct pwrseq_target_data *data)
{
	struct radix_tree_root visited_units;
	struct radix_tree_iter iter;
	void __rcu **slot;
	int ret;

	if (!data->unit)
		return -EINVAL;

	INIT_RADIX_TREE(&visited_units, GFP_KERNEL);
	ret = pwrseq_check_unit_deps(data->unit, &visited_units);
	radix_tree_for_each_slot(slot, &visited_units, &iter, 0)
		radix_tree_delete(&visited_units, iter.index);

	return ret;
}

static int pwrseq_unit_setup_deps(const struct pwrseq_unit_data **data,
				  struct list_head *dep_list,
				  struct list_head *unit_list,
				  struct radix_tree_root *processed_units);

static struct pwrseq_unit *
pwrseq_unit_setup(const struct pwrseq_unit_data *data,
		  struct list_head *unit_list,
		  struct radix_tree_root *processed_units)
{
	struct pwrseq_unit *unit;
	int ret;

	unit = radix_tree_lookup(processed_units, (unsigned long)data);
	if (unit)
		return pwrseq_unit_get(unit);

	unit = pwrseq_unit_new(data);
	if (!unit)
		return ERR_PTR(-ENOMEM);

	if (data->deps) {
		ret = pwrseq_unit_setup_deps(data->deps, &unit->deps,
					     unit_list, processed_units);
		if (ret) {
			pwrseq_unit_put(unit);
			return ERR_PTR(ret);
		}
	}

	ret = radix_tree_insert(processed_units, (unsigned long)data, unit);
	if (ret) {
		pwrseq_unit_put(unit);
		return ERR_PTR(ret);
	}

	list_add_tail(&unit->list, unit_list);

	return unit;
}

static int pwrseq_unit_setup_deps(const struct pwrseq_unit_data **data,
				  struct list_head *dep_list,
				  struct list_head *unit_list,
				  struct radix_tree_root *processed_units)
{
	const struct pwrseq_unit_data *pos;
	struct pwrseq_unit_dep *dep;
	struct pwrseq_unit *unit;
	int i;

	for (i = 0; data[i]; i++) {
		pos = data[i];

		unit = pwrseq_unit_setup(pos, unit_list, processed_units);
		if (IS_ERR(unit))
			return PTR_ERR(unit);

		dep = pwrseq_unit_dep_new(unit);
		if (!dep) {
			pwrseq_unit_put(unit);
			return -ENOMEM;
		}

		list_add_tail(&dep->list, dep_list);
	}

	return 0;
}

static int pwrseq_do_setup_targets(const struct pwrseq_target_data **data,
				   struct pwrseq_device *pwrseq,
				   struct radix_tree_root *processed_units)
{
	const struct pwrseq_target_data *pos;
	struct pwrseq_target *target;
	int ret, i;

	for (i = 0; data[i]; i++) {
		pos = data[i];

		ret = pwrseq_check_target_deps(pos);
		if (ret)
			return ret;

		target = pwrseq_target_new(pos);
		if (!target)
			return -ENOMEM;

		target->unit = pwrseq_unit_setup(pos->unit, &pwrseq->units,
						 processed_units);
		if (IS_ERR(target->unit)) {
			ret = PTR_ERR(target->unit);
			pwrseq_target_free(target);
			return ret;
		}

		list_add_tail(&target->list, &pwrseq->targets);
	}

	return 0;
}

static int pwrseq_setup_targets(const struct pwrseq_target_data **targets,
				struct pwrseq_device *pwrseq)
{
	struct radix_tree_root processed_units;
	struct radix_tree_iter iter;
	void __rcu **slot;
	int ret;

	INIT_RADIX_TREE(&processed_units, GFP_KERNEL);
	ret = pwrseq_do_setup_targets(targets, pwrseq, &processed_units);
	radix_tree_for_each_slot(slot, &processed_units, &iter, 0)
		radix_tree_delete(&processed_units, iter.index);

	return ret;
}

/**
 * pwrseq_device_register() - Register a new power sequencer.
 * @config: Configuration of the new power sequencing device.
 *
 * The config structure is only used during the call and can be freed after
 * the function returns. The config structure *must* have the parent device
 * as well as the match() callback and at least one target set.
 *
 * Returns:
 * Returns the address of the new pwrseq device or ERR_PTR() on failure.
 */
struct pwrseq_device *
pwrseq_device_register(const struct pwrseq_config *config)
{
	struct pwrseq_device *pwrseq;
	int ret, id;

	if (!config->parent || !config->match || !config->targets ||
	    !config->targets[0])
		return ERR_PTR(-EINVAL);

	pwrseq = kzalloc(sizeof(*pwrseq), GFP_KERNEL);
	if (!pwrseq)
		return ERR_PTR(-ENOMEM);

	pwrseq->dev.type = &pwrseq_device_type;
	pwrseq->dev.bus = &pwrseq_bus;
	pwrseq->dev.parent = config->parent;
	device_set_node(&pwrseq->dev, dev_fwnode(config->parent));
	dev_set_drvdata(&pwrseq->dev, config->drvdata);

	id = ida_alloc(&pwrseq_ida, GFP_KERNEL);
	if (id < 0) {
		kfree(pwrseq);
		return ERR_PTR(id);
	}

	pwrseq->id = id;

	/*
	 * From this point onwards the device's release() callback is
	 * responsible for freeing resources.
	 */
	device_initialize(&pwrseq->dev);

	ret = dev_set_name(&pwrseq->dev, "pwrseq.%d", pwrseq->id);
	if (ret)
		goto err_put_pwrseq;

	pwrseq->owner = config->owner ?: THIS_MODULE;
	pwrseq->match = config->match;

	init_rwsem(&pwrseq->rw_lock);
	mutex_init(&pwrseq->state_lock);
	INIT_LIST_HEAD(&pwrseq->targets);
	INIT_LIST_HEAD(&pwrseq->units);

	ret = pwrseq_setup_targets(config->targets, pwrseq);
	if (ret)
		goto err_put_pwrseq;

	scoped_guard(rwsem_write, &pwrseq_sem) {
		ret = device_add(&pwrseq->dev);
		if (ret)
			goto err_put_pwrseq;
	}

	return pwrseq;

err_put_pwrseq:
	pwrseq_device_put(pwrseq);
	return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(pwrseq_device_register);

/**
 * pwrseq_device_unregister() - Unregister the power sequencer.
 * @pwrseq: Power sequencer to unregister.
 */
void pwrseq_device_unregister(struct pwrseq_device *pwrseq)
{
	struct device *dev = &pwrseq->dev;
	struct pwrseq_target *target;

	scoped_guard(mutex, &pwrseq->state_lock) {
		guard(rwsem_write)(&pwrseq->rw_lock);

		list_for_each_entry(target, &pwrseq->targets, list)
			WARN(target->unit->enable_count,
			     "REMOVING POWER SEQUENCER WITH ACTIVE USERS\n");

		guard(rwsem_write)(&pwrseq_sem);

		device_del(dev);
	}

	pwrseq_device_put(pwrseq);
}
EXPORT_SYMBOL_GPL(pwrseq_device_unregister);

static void devm_pwrseq_device_unregister(void *data)
{
	struct pwrseq_device *pwrseq = data;

	pwrseq_device_unregister(pwrseq);
}

/**
 * devm_pwrseq_device_register() - Managed variant of pwrseq_device_register().
 * @dev: Managing device.
 * @config: Configuration of the new power sequencing device.
 *
 * Returns:
 * Returns the address of the new pwrseq device or ERR_PTR() on failure.
 */
struct pwrseq_device *
devm_pwrseq_device_register(struct device *dev,
			    const struct pwrseq_config *config)
{
	struct pwrseq_device *pwrseq;
	int ret;

	pwrseq = pwrseq_device_register(config);
	if (IS_ERR(pwrseq))
		return pwrseq;

	ret = devm_add_action_or_reset(dev, devm_pwrseq_device_unregister,
				       pwrseq);
	if (ret)
		return ERR_PTR(ret);

	return pwrseq;
}
EXPORT_SYMBOL_GPL(devm_pwrseq_device_register);

/**
 * pwrseq_device_get_drvdata() - Get the driver private data associated with
 *                               this sequencer.
 * @pwrseq: Power sequencer object.
 *
 * Returns:
 * Address of the private driver data.
 */
void *pwrseq_device_get_drvdata(struct pwrseq_device *pwrseq)
{
	return dev_get_drvdata(&pwrseq->dev);
}
EXPORT_SYMBOL_GPL(pwrseq_device_get_drvdata);

struct pwrseq_match_data {
	struct pwrseq_desc *desc;
	struct device *dev;
	const char *target;
};

static int pwrseq_match_device(struct device *pwrseq_dev, void *data)
{
	struct pwrseq_device *pwrseq = to_pwrseq_device(pwrseq_dev);
	struct pwrseq_match_data *match_data = data;
	struct pwrseq_target *target;
	int ret;

	lockdep_assert_held_read(&pwrseq_sem);

	guard(rwsem_read)(&pwrseq->rw_lock);
	if (!device_is_registered(&pwrseq->dev))
		return 0;

	ret = pwrseq->match(pwrseq, match_data->dev);
	if (ret <= 0)
		return ret;

	/* We got the matching device, let's find the right target. */
	list_for_each_entry(target, &pwrseq->targets, list) {
		if (strcmp(target->name, match_data->target))
			continue;

		match_data->desc->target = target;
	}

	/*
	 * This device does not have this target. No point in deferring as it
	 * will not get a new target dynamically later.
	 */
	if (!match_data->desc->target)
		return -ENOENT;

	if (!try_module_get(pwrseq->owner))
		return -EPROBE_DEFER;

	match_data->desc->pwrseq = pwrseq_device_get(pwrseq);

	return 1;
}

/**
 * pwrseq_get() - Get the power sequencer associated with this device.
 * @dev: Device for which to get the sequencer.
 * @target: Name of the target exposed by the sequencer this device wants to
 *          reach.
 *
 * Returns:
 * New power sequencer descriptor for use by the consumer driver or ERR_PTR()
 * on failure.
 */
struct pwrseq_desc *pwrseq_get(struct device *dev, const char *target)
{
	struct pwrseq_match_data match_data;
	int ret;

	struct pwrseq_desc *desc __free(kfree) = kzalloc(sizeof(*desc),
							 GFP_KERNEL);
	if (!desc)
		return ERR_PTR(-ENOMEM);

	match_data.desc = desc;
	match_data.dev = dev;
	match_data.target = target;

	guard(rwsem_read)(&pwrseq_sem);

	ret = bus_for_each_dev(&pwrseq_bus, NULL, &match_data,
			       pwrseq_match_device);
	if (ret < 0)
		return ERR_PTR(ret);
	if (ret == 0)
		/* No device matched. */
		return ERR_PTR(-EPROBE_DEFER);

	return_ptr(desc);
}
EXPORT_SYMBOL_GPL(pwrseq_get);

/**
 * pwrseq_put() - Release the power sequencer descriptor.
 * @desc: Descriptor to release.
 */
void pwrseq_put(struct pwrseq_desc *desc)
{
	struct pwrseq_device *pwrseq;

	if (!desc)
		return;

	pwrseq = desc->pwrseq;

	if (desc->powered_on)
		pwrseq_power_off(desc);

	kfree(desc);
	module_put(pwrseq->owner);
	pwrseq_device_put(pwrseq);
}
EXPORT_SYMBOL_GPL(pwrseq_put);

static void devm_pwrseq_put(void *data)
{
	struct pwrseq_desc *desc = data;

	pwrseq_put(desc);
}

/**
 * devm_pwrseq_get() - Managed variant of pwrseq_get().
 * @dev: Device for which to get the sequencer and which also manages its
 *       lifetime.
 * @target: Name of the target exposed by the sequencer this device wants to
 *          reach.
 *
 * Returns:
 * New power sequencer descriptor for use by the consumer driver or ERR_PTR()
 * on failure.
 */
struct pwrseq_desc *devm_pwrseq_get(struct device *dev, const char *target)
{
	struct pwrseq_desc *desc;
	int ret;

	desc = pwrseq_get(dev, target);
	if (IS_ERR(desc))
		return desc;

	ret = devm_add_action_or_reset(dev, devm_pwrseq_put, desc);
	if (ret)
		return ERR_PTR(ret);

	return desc;
}
EXPORT_SYMBOL_GPL(devm_pwrseq_get);

static int pwrseq_unit_enable(struct pwrseq_device *pwrseq,
			      struct pwrseq_unit *target);
static int pwrseq_unit_disable(struct pwrseq_device *pwrseq,
			       struct pwrseq_unit *target);

static int pwrseq_unit_enable_deps(struct pwrseq_device *pwrseq,
				   struct list_head *list)
{
	struct pwrseq_unit_dep *pos;
	int ret = 0;

	list_for_each_entry(pos, list, list) {
		ret = pwrseq_unit_enable(pwrseq, pos->unit);
		if (ret) {
			list_for_each_entry_continue_reverse(pos, list, list)
				pwrseq_unit_disable(pwrseq, pos->unit);
			break;
		}
	}

	return ret;
}

static int pwrseq_unit_disable_deps(struct pwrseq_device *pwrseq,
				    struct list_head *list)
{
	struct pwrseq_unit_dep *pos;
	int ret = 0;

	list_for_each_entry_reverse(pos, list, list) {
		ret = pwrseq_unit_disable(pwrseq, pos->unit);
		if (ret) {
			list_for_each_entry_continue(pos, list, list)
				pwrseq_unit_enable(pwrseq, pos->unit);
			break;
		}
	}

	return ret;
}

static int pwrseq_unit_enable(struct pwrseq_device *pwrseq,
			      struct pwrseq_unit *unit)
{
	int ret;

	lockdep_assert_held_read(&pwrseq->rw_lock);
	lockdep_assert_held(&pwrseq->state_lock);

	if (unit->enable_count != 0) {
		unit->enable_count++;
		return 0;
	}

	ret = pwrseq_unit_enable_deps(pwrseq, &unit->deps);
	if (ret) {
		dev_err(&pwrseq->dev,
			"Failed to enable dependencies before power-on for target '%s': %d\n",
			unit->name, ret);
		return ret;
	}

	if (unit->enable) {
		ret = unit->enable(pwrseq);
		if (ret) {
			dev_err(&pwrseq->dev,
				"Failed to enable target '%s': %d\n",
				unit->name, ret);
			pwrseq_unit_disable_deps(pwrseq, &unit->deps);
			return ret;
		}
	}

	unit->enable_count++;

	return 0;
}

static int pwrseq_unit_disable(struct pwrseq_device *pwrseq,
			       struct pwrseq_unit *unit)
{
	int ret;

	lockdep_assert_held_read(&pwrseq->rw_lock);
	lockdep_assert_held(&pwrseq->state_lock);

	if (unit->enable_count == 0) {
		WARN(1, "Unmatched power-off for target '%s'\n",
		     unit->name);
		return -EBUSY;
	}

	if (unit->enable_count != 1) {
		unit->enable_count--;
		return 0;
	}

	if (unit->disable) {
		ret = unit->disable(pwrseq);
		if (ret) {
			dev_err(&pwrseq->dev,
				"Failed to disable target '%s': %d\n",
				unit->name, ret);
			return ret;
		}
	}

	ret = pwrseq_unit_disable_deps(pwrseq, &unit->deps);
	if (ret) {
		dev_err(&pwrseq->dev,
			"Failed to disable dependencies after power-off for target '%s': %d\n",
			unit->name, ret);
		if (unit->enable)
			unit->enable(pwrseq);
		return ret;
	}

	unit->enable_count--;

	return 0;
}

/**
 * pwrseq_power_on() - Issue a power-on request on behalf of the consumer
 *                     device.
 * @desc: Descriptor referencing the power sequencer.
 *
 * This function tells the power sequencer that the consumer wants to be
 * powered-up. The sequencer may already have powered-up the device in which
 * case the function returns 0. If the power-up sequence is already in
 * progress, the function will block until it's done and return 0. If this is
 * the first request, the device will be powered up.
 *
 * Returns:
 * 0 on success, negative error number on failure.
 */
int pwrseq_power_on(struct pwrseq_desc *desc)
{
	struct pwrseq_device *pwrseq;
	struct pwrseq_target *target;
	struct pwrseq_unit *unit;
	int ret;

	might_sleep();

	if (!desc || desc->powered_on)
		return 0;

	pwrseq = desc->pwrseq;
	target = desc->target;
	unit = target->unit;

	guard(rwsem_read)(&pwrseq->rw_lock);
	if (!device_is_registered(&pwrseq->dev))
		return -ENODEV;

	scoped_guard(mutex, &pwrseq->state_lock) {
		ret = pwrseq_unit_enable(pwrseq, unit);
		if (!ret)
			desc->powered_on = true;
	}

	if (target->post_enable) {
		ret = target->post_enable(pwrseq);
		if (ret) {
			pwrseq_unit_disable(pwrseq, unit);
			desc->powered_on = false;
		}
	}

	return ret;
}
EXPORT_SYMBOL_GPL(pwrseq_power_on);

/**
 * pwrseq_power_off() - Issue a power-off request on behalf of the consumer
 *                      device.
 * @desc: Descriptor referencing the power sequencer.
 *
 * This undoes the effects of pwrseq_power_on(). It issues a power-off request
 * on behalf of the consumer and when the last remaining user does so, the
 * power-down sequence will be started. If one is in progress, the function
 * will block until it's complete and then return.
 *
 * Returns:
 * 0 on success, negative error number on failure.
 */
int pwrseq_power_off(struct pwrseq_desc *desc)
{
	struct pwrseq_device *pwrseq;
	struct pwrseq_unit *unit;
	int ret;

	might_sleep();

	if (!desc || !desc->powered_on)
		return 0;

	pwrseq = desc->pwrseq;
	unit = desc->target->unit;

	guard(rwsem_read)(&pwrseq->rw_lock);
	if (!device_is_registered(&pwrseq->dev))
		return -ENODEV;

	guard(mutex)(&pwrseq->state_lock);

	ret = pwrseq_unit_disable(pwrseq, unit);
	if (!ret)
		desc->powered_on = false;

	return ret;
}
EXPORT_SYMBOL_GPL(pwrseq_power_off);

#if IS_ENABLED(CONFIG_DEBUG_FS)

struct pwrseq_debugfs_count_ctx {
	struct device *dev;
	loff_t index;
};

static int pwrseq_debugfs_seq_count(struct device *dev, void *data)
{
	struct pwrseq_debugfs_count_ctx *ctx = data;

	ctx->dev = dev;

	return ctx->index-- ? 0 : 1;
}

static void *pwrseq_debugfs_seq_start(struct seq_file *seq, loff_t *pos)
{
	struct pwrseq_debugfs_count_ctx ctx;

	ctx.dev = NULL;
	ctx.index = *pos;

	/*
	 * We're holding the lock for the entire printout so no need to fiddle
	 * with device reference count.
	 */
	down_read(&pwrseq_sem);

	bus_for_each_dev(&pwrseq_bus, NULL, &ctx, pwrseq_debugfs_seq_count);
	if (!ctx.index)
		return NULL;

	return ctx.dev;
}

static void *pwrseq_debugfs_seq_next(struct seq_file *seq, void *data,
				     loff_t *pos)
{
	struct device *curr = data;

	++*pos;

	struct device *next __free(put_device) =
			bus_find_next_device(&pwrseq_bus, curr);
	return next;
}

static void pwrseq_debugfs_seq_show_target(struct seq_file *seq,
					   struct pwrseq_target *target)
{
	seq_printf(seq, "    target: [%s] (target unit: [%s])\n",
		   target->name, target->unit->name);
}

static void pwrseq_debugfs_seq_show_unit(struct seq_file *seq,
					 struct pwrseq_unit *unit)
{
	struct pwrseq_unit_dep *ref;

	seq_printf(seq, "    unit: [%s] - enable count: %u\n",
		   unit->name, unit->enable_count);

	if (list_empty(&unit->deps))
		return;

	seq_puts(seq, "      dependencies:\n");
	list_for_each_entry(ref, &unit->deps, list)
		seq_printf(seq, "        [%s]\n", ref->unit->name);
}

static int pwrseq_debugfs_seq_show(struct seq_file *seq, void *data)
{
	struct device *dev = data;
	struct pwrseq_device *pwrseq = to_pwrseq_device(dev);
	struct pwrseq_target *target;
	struct pwrseq_unit *unit;

	seq_printf(seq, "%s:\n", dev_name(dev));

	seq_puts(seq, "  targets:\n");
	list_for_each_entry(target, &pwrseq->targets, list)
		pwrseq_debugfs_seq_show_target(seq, target);

	seq_puts(seq, "  units:\n");
	list_for_each_entry(unit, &pwrseq->units, list)
		pwrseq_debugfs_seq_show_unit(seq, unit);

	return 0;
}

static void pwrseq_debugfs_seq_stop(struct seq_file *seq, void *data)
{
	up_read(&pwrseq_sem);
}

static const struct seq_operations pwrseq_debugfs_sops = {
	.start = pwrseq_debugfs_seq_start,
	.next = pwrseq_debugfs_seq_next,
	.show = pwrseq_debugfs_seq_show,
	.stop = pwrseq_debugfs_seq_stop,
};
DEFINE_SEQ_ATTRIBUTE(pwrseq_debugfs);

static struct dentry *pwrseq_debugfs_dentry;

#endif /* CONFIG_DEBUG_FS */

static int __init pwrseq_init(void)
{
	int ret;

	ret = bus_register(&pwrseq_bus);
	if (ret) {
		pr_err("Failed to register the power sequencer bus\n");
		return ret;
	}

#if IS_ENABLED(CONFIG_DEBUG_FS)
	pwrseq_debugfs_dentry = debugfs_create_file("pwrseq", 0444, NULL, NULL,
						    &pwrseq_debugfs_fops);
#endif  /* CONFIG_DEBUG_FS */

	return 0;
}
subsys_initcall(pwrseq_init);

static void __exit pwrseq_exit(void)
{
#if IS_ENABLED(CONFIG_DEBUG_FS)
	debugfs_remove_recursive(pwrseq_debugfs_dentry);
#endif  /* CONFIG_DEBUG_FS */

	bus_unregister(&pwrseq_bus);
}
module_exit(pwrseq_exit);

MODULE_AUTHOR("Bartosz Golaszewski <bartosz.golaszewski@linaro.org>");
MODULE_DESCRIPTION("Power Sequencing subsystem core");
MODULE_LICENSE("GPL");