linux/drivers/gpu/drm/dp/drm_dp_aux_bus.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright 2021 Google Inc.
 *
 * The DP AUX bus is used for devices that are connected over a DisplayPort
 * AUX bus. The devices on the far side of the bus are referred to as
 * endpoints in this code.
 *
 * Commonly there is only one device connected to the DP AUX bus: a panel.
 * Though historically panels (even DP panels) have been modeled as simple
 * platform devices, putting them under the DP AUX bus allows the panel driver
 * to perform transactions on that bus.
 */

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of_device.h>
#include <linux/pm_domain.h>
#include <linux/pm_runtime.h>

#include <drm/dp/drm_dp_aux_bus.h>
#include <drm/dp/drm_dp_helper.h>

/**
 * dp_aux_ep_match() - The match function for the dp_aux_bus.
 * @dev: The device to match.
 * @drv: The driver to try to match against.
 *
 * At the moment, we just match on device tree.
 *
 * Return: True if this driver matches this device; false otherwise.
 */
static int dp_aux_ep_match(struct device *dev, struct device_driver *drv)
{
	return !!of_match_device(drv->of_match_table, dev);
}

/**
 * dp_aux_ep_probe() - The probe function for the dp_aux_bus.
 * @dev: The device to probe.
 *
 * Calls through to the endpoint driver probe.
 *
 * Return: 0 if no error or negative error code.
 */
static int dp_aux_ep_probe(struct device *dev)
{
	struct dp_aux_ep_driver *aux_ep_drv = to_dp_aux_ep_drv(dev->driver);
	struct dp_aux_ep_device *aux_ep = to_dp_aux_ep_dev(dev);
	int ret;

	ret = dev_pm_domain_attach(dev, true);
	if (ret)
		return dev_err_probe(dev, ret, "Failed to attach to PM Domain\n");

	ret = aux_ep_drv->probe(aux_ep);
	if (ret)
		dev_pm_domain_detach(dev, true);

	return ret;
}

/**
 * dp_aux_ep_remove() - The remove function for the dp_aux_bus.
 * @dev: The device to remove.
 *
 * Calls through to the endpoint driver remove.
 *
 */
static void dp_aux_ep_remove(struct device *dev)
{
	struct dp_aux_ep_driver *aux_ep_drv = to_dp_aux_ep_drv(dev->driver);
	struct dp_aux_ep_device *aux_ep = to_dp_aux_ep_dev(dev);

	if (aux_ep_drv->remove)
		aux_ep_drv->remove(aux_ep);
	dev_pm_domain_detach(dev, true);
}

/**
 * dp_aux_ep_shutdown() - The shutdown function for the dp_aux_bus.
 * @dev: The device to shutdown.
 *
 * Calls through to the endpoint driver shutdown.
 */
static void dp_aux_ep_shutdown(struct device *dev)
{
	struct dp_aux_ep_driver *aux_ep_drv;

	if (!dev->driver)
		return;

	aux_ep_drv = to_dp_aux_ep_drv(dev->driver);
	if (aux_ep_drv->shutdown)
		aux_ep_drv->shutdown(to_dp_aux_ep_dev(dev));
}

static struct bus_type dp_aux_bus_type = {
	.name		= "dp-aux",
	.match		= dp_aux_ep_match,
	.probe		= dp_aux_ep_probe,
	.remove		= dp_aux_ep_remove,
	.shutdown	= dp_aux_ep_shutdown,
};

static ssize_t modalias_show(struct device *dev,
			     struct device_attribute *attr, char *buf)
{
	return of_device_modalias(dev, buf, PAGE_SIZE);
}
static DEVICE_ATTR_RO(modalias);

static struct attribute *dp_aux_ep_dev_attrs[] = {
	&dev_attr_modalias.attr,
	NULL,
};
ATTRIBUTE_GROUPS(dp_aux_ep_dev);

/**
 * dp_aux_ep_dev_release() - Free memory for the dp_aux_ep device
 * @dev: The device to free.
 *
 * Return: 0 if no error or negative error code.
 */
static void dp_aux_ep_dev_release(struct device *dev)
{
	kfree(to_dp_aux_ep_dev(dev));
}

static struct device_type dp_aux_device_type_type = {
	.groups		= dp_aux_ep_dev_groups,
	.uevent		= of_device_uevent_modalias,
	.release	= dp_aux_ep_dev_release,
};

/**
 * of_dp_aux_ep_destroy() - Destroy an DP AUX endpoint device
 * @dev: The device to destroy.
 * @data: Not used
 *
 * This is just used as a callback by of_dp_aux_depopulate_ep_devices() and
 * is called for _all_ of the child devices of the device providing the AUX bus.
 * We'll only act on those that are of type "dp_aux_bus_type".
 *
 * This function is effectively an inverse of what's in the loop
 * in of_dp_aux_populate_ep_devices().
 *
 * Return: 0 if no error or negative error code.
 */
static int of_dp_aux_ep_destroy(struct device *dev, void *data)
{
	struct device_node *np = dev->of_node;

	if (dev->bus != &dp_aux_bus_type)
		return 0;

	if (!of_node_check_flag(np, OF_POPULATED))
		return 0;

	of_node_clear_flag(np, OF_POPULATED);
	of_node_put(np);

	device_unregister(dev);

	return 0;
}

/**
 * of_dp_aux_depopulate_ep_devices() - Undo of_dp_aux_populate_ep_devices
 * @aux: The AUX channel whose devices we want to depopulate
 *
 * This will destroy all devices that were created
 * by of_dp_aux_populate_ep_devices().
 */
void of_dp_aux_depopulate_ep_devices(struct drm_dp_aux *aux)
{
	device_for_each_child_reverse(aux->dev, NULL, of_dp_aux_ep_destroy);
}
EXPORT_SYMBOL_GPL(of_dp_aux_depopulate_ep_devices);

/**
 * of_dp_aux_populate_ep_devices() - Populate the endpoint devices on the DP AUX
 * @aux: The AUX channel whose devices we want to populate. It is required that
 *       drm_dp_aux_init() has already been called for this AUX channel.
 *
 * This will populate all the devices under the "aux-bus" node of the device
 * providing the AUX channel (AKA aux->dev).
 *
 * When this function finishes, it is _possible_ (but not guaranteed) that
 * our sub-devices will have finished probing. It should be noted that if our
 * sub-devices return -EPROBE_DEFER that we will not return any error codes
 * ourselves but our sub-devices will _not_ have actually probed successfully
 * yet. There may be other cases (maybe added in the future?) where sub-devices
 * won't have been probed yet when this function returns, so it's best not to
 * rely on that.
 *
 * If this function succeeds you should later make sure you call
 * of_dp_aux_depopulate_ep_devices() to undo it, or just use the devm version
 * of this function.
 *
 * Return: 0 if no error or negative error code.
 */
int of_dp_aux_populate_ep_devices(struct drm_dp_aux *aux)
{
	struct device_node *bus, *np;
	struct dp_aux_ep_device *aux_ep;
	int ret;

	/* drm_dp_aux_init() should have been called already; warn if not */
	WARN_ON_ONCE(!aux->ddc.algo);

	if (!aux->dev->of_node)
		return 0;

	bus = of_get_child_by_name(aux->dev->of_node, "aux-bus");
	if (!bus)
		return 0;

	for_each_available_child_of_node(bus, np) {
		if (of_node_test_and_set_flag(np, OF_POPULATED))
			continue;

		aux_ep = kzalloc(sizeof(*aux_ep), GFP_KERNEL);
		if (!aux_ep)
			continue;
		aux_ep->aux = aux;

		aux_ep->dev.parent = aux->dev;
		aux_ep->dev.bus = &dp_aux_bus_type;
		aux_ep->dev.type = &dp_aux_device_type_type;
		aux_ep->dev.of_node = of_node_get(np);
		dev_set_name(&aux_ep->dev, "aux-%s", dev_name(aux->dev));

		ret = device_register(&aux_ep->dev);
		if (ret) {
			dev_err(aux->dev, "Failed to create AUX EP for %pOF: %d\n", np, ret);
			of_node_clear_flag(np, OF_POPULATED);
			of_node_put(np);

			/*
			 * As per docs of device_register(), call this instead
			 * of kfree() directly for error cases.
			 */
			put_device(&aux_ep->dev);

			/*
			 * Following in the footsteps of of_i2c_register_devices(),
			 * we won't fail the whole function here--we'll just
			 * continue registering any other devices we find.
			 */
		}
	}

	of_node_put(bus);

	return 0;
}

static void of_dp_aux_depopulate_ep_devices_void(void *data)
{
	of_dp_aux_depopulate_ep_devices(data);
}

/**
 * devm_of_dp_aux_populate_ep_devices() - devm wrapper for of_dp_aux_populate_ep_devices()
 * @aux: The AUX channel whose devices we want to populate
 *
 * Handles freeing w/ devm on the device "aux->dev".
 *
 * Return: 0 if no error or negative error code.
 */
int devm_of_dp_aux_populate_ep_devices(struct drm_dp_aux *aux)
{
	int ret;

	ret = of_dp_aux_populate_ep_devices(aux);
	if (ret)
		return ret;

	return devm_add_action_or_reset(aux->dev,
					of_dp_aux_depopulate_ep_devices_void,
					aux);
}
EXPORT_SYMBOL_GPL(devm_of_dp_aux_populate_ep_devices);

int __dp_aux_dp_driver_register(struct dp_aux_ep_driver *drv, struct module *owner)
{
	drv->driver.owner = owner;
	drv->driver.bus = &dp_aux_bus_type;

	return driver_register(&drv->driver);
}
EXPORT_SYMBOL_GPL(__dp_aux_dp_driver_register);

void dp_aux_dp_driver_unregister(struct dp_aux_ep_driver *drv)
{
	driver_unregister(&drv->driver);
}
EXPORT_SYMBOL_GPL(dp_aux_dp_driver_unregister);

static int __init dp_aux_bus_init(void)
{
	int ret;

	ret = bus_register(&dp_aux_bus_type);
	if (ret)
		return ret;

	return 0;
}

static void __exit dp_aux_bus_exit(void)
{
	bus_unregister(&dp_aux_bus_type);
}

subsys_initcall(dp_aux_bus_init);
module_exit(dp_aux_bus_exit);

MODULE_AUTHOR("Douglas Anderson <dianders@chromium.org>");
MODULE_DESCRIPTION("DRM DisplayPort AUX bus");
MODULE_LICENSE("GPL v2");