// 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 device on the far side of the bus is referred to as an
 * endpoint in this code.
 *
 * There is only one device connected to the DP AUX bus: an eDP 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/export.h>
#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/display/drm_dp_aux_bus.h>
#include <drm/display/drm_dp_helper.h>

struct dp_aux_ep_device_with_data {
        struct dp_aux_ep_device aux_ep;
        int (*done_probing)(struct drm_dp_aux *aux);
};

/**
 * 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, const 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);
        struct dp_aux_ep_device_with_data *aux_ep_with_data =
                container_of(aux_ep, struct dp_aux_ep_device_with_data, aux_ep);
        int ret;

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

        ret = aux_ep_drv->probe(aux_ep);
        if (ret)
                goto err_attached;

        if (aux_ep_with_data->done_probing) {
                ret = aux_ep_with_data->done_probing(aux_ep->aux);
                if (ret) {
                        /*
                         * The done_probing() callback should not return
                         * -EPROBE_DEFER to us. If it does, we treat it as an
                         * error. Passing it on as-is would cause the _panel_
                         * to defer.
                         */
                        if (ret == -EPROBE_DEFER) {
                                dev_err(dev,
                                        "DP AUX done_probing() can't defer\n");
                                ret = -EINVAL;
                        }
                        goto err_probed;
                }
        }

        return 0;
err_probed:
        if (aux_ep_drv->remove)
                aux_ep_drv->remove(aux_ep);
err_attached:
        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 const 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.
 */
static void dp_aux_ep_dev_release(struct device *dev)
{
        struct dp_aux_ep_device *aux_ep = to_dp_aux_ep_dev(dev);
        struct dp_aux_ep_device_with_data *aux_ep_with_data =
                container_of(aux_ep, struct dp_aux_ep_device_with_data, aux_ep);

        kfree(aux_ep_with_data);
}

static int dp_aux_ep_dev_modalias(const struct device *dev, struct kobj_uevent_env *env)
{
        return of_device_uevent_modalias(dev, env);
}

static struct device_type dp_aux_device_type_type = {
        .groups         = dp_aux_ep_dev_groups,
        .uevent         = dp_aux_ep_dev_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_bus() 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
 * of_dp_aux_populate_bus(). NOTE: since we only populate one child
 * then it's expected that only one device will match all the "if" tests in
 * this function and get to the device_unregister().
 *
 * 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_bus() - Undo of_dp_aux_populate_bus
 * @aux: The AUX channel whose device we want to depopulate
 *
 * This will destroy the device that was created
 * by of_dp_aux_populate_bus().
 */
void of_dp_aux_depopulate_bus(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_bus);

/**
 * of_dp_aux_populate_bus() - Populate the endpoint device on the DP AUX
 * @aux: The AUX channel whose device we want to populate. It is required that
 *       drm_dp_aux_init() has already been called for this AUX channel.
 * @done_probing: Callback functions to call after EP device finishes probing.
 *                Will not be called if there are no EP devices and this
 *                function will return -ENODEV.
 *
 * This will populate the device (expected to be an eDP panel) 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-device will have finished probing. It should be noted that if our
 * sub-device returns -EPROBE_DEFER or is probing asynchronously for some
 * reason that we will not return any error codes ourselves but our
 * sub-device will _not_ have actually probed successfully yet.
 *
 * In many cases it's important for the caller of this function to be notified
 * when our sub device finishes probing. Our sub device is expected to be an
 * eDP panel and the caller is expected to be an eDP controller. The eDP
 * controller needs to be able to get a reference to the panel when it finishes
 * probing. For this reason the caller can pass in a function pointer that
 * will be called when our sub-device finishes probing.
 *
 * If this function succeeds you should later make sure you call
 * of_dp_aux_depopulate_bus() to undo it, or just use the devm version
 * of this function.
 *
 * Return: 0 if no error or negative error code; returns -ENODEV if there are
 *         no children. The done_probing() function won't be called in that
 *         case.
 */
int of_dp_aux_populate_bus(struct drm_dp_aux *aux,
                           int (*done_probing)(struct drm_dp_aux *aux))
{
        struct device_node *bus = NULL, *np = NULL;
        struct dp_aux_ep_device *aux_ep;
        struct dp_aux_ep_device_with_data *aux_ep_with_data;
        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 -ENODEV;
        bus = of_get_child_by_name(aux->dev->of_node, "aux-bus");
        if (!bus)
                return -ENODEV;

        np = of_get_next_available_child(bus, NULL);
        of_node_put(bus);
        if (!np)
                return -ENODEV;

        if (of_node_test_and_set_flag(np, OF_POPULATED)) {
                dev_err(aux->dev, "DP AUX EP device already populated\n");
                ret = -EINVAL;
                goto err_did_get_np;
        }

        aux_ep_with_data = kzalloc_obj(*aux_ep_with_data);
        if (!aux_ep_with_data) {
                ret = -ENOMEM;
                goto err_did_set_populated;
        }

        aux_ep_with_data->done_probing = done_probing;

        aux_ep = &aux_ep_with_data->aux_ep;
        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;
        device_set_node(&aux_ep->dev, of_fwnode_handle(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);

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

                goto err_did_set_populated;
        }

        return 0;

err_did_set_populated:
        of_node_clear_flag(np, OF_POPULATED);

err_did_get_np:
        of_node_put(np);

        return ret;
}
EXPORT_SYMBOL_GPL(of_dp_aux_populate_bus);

static void of_dp_aux_depopulate_bus_void(void *data)
{
        of_dp_aux_depopulate_bus(data);
}

/**
 * devm_of_dp_aux_populate_bus() - devm wrapper for of_dp_aux_populate_bus()
 * @aux: The AUX channel whose device we want to populate
 * @done_probing: Callback functions to call after EP device finishes probing.
 *                Will not be called if there are no EP devices and this
 *                function will return -ENODEV.
 *
 * Handles freeing w/ devm on the device "aux->dev".
 *
 * Return: 0 if no error or negative error code; returns -ENODEV if there are
 *         no children. The done_probing() function won't be called in that
 *         case.
 */
int devm_of_dp_aux_populate_bus(struct drm_dp_aux *aux,
                                int (*done_probing)(struct drm_dp_aux *aux))
{
        int ret;

        ret = of_dp_aux_populate_bus(aux, done_probing);
        if (ret)
                return ret;

        return devm_add_action_or_reset(aux->dev,
                                        of_dp_aux_depopulate_bus_void, aux);
}
EXPORT_SYMBOL_GPL(devm_of_dp_aux_populate_bus);

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");