drivers/platform/surface/aggregator/core.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Surface Serial Hub (SSH) driver for communication with the Surface/System
 * Aggregator Module (SSAM/SAM).
 *
 * Provides access to a SAM-over-SSH connected EC via a controller device.
 * Handles communication via requests as well as enabling, disabling, and
 * relaying of events.
 *
 * Copyright (C) 2019-2021 Maximilian Luz <luzmaximilian@gmail.com>
 */

#include <linux/acpi.h>
#include <linux/atomic.h>
#include <linux/completion.h>
#include <linux/gpio/consumer.h>
#include <linux/kernel.h>
#include <linux/kref.h>
#include <linux/module.h>
#include <linux/pm.h>
#include <linux/serdev.h>
#include <linux/sysfs.h>

#include <linux/surface_aggregator/controller.h>

#include "bus.h"
#include "controller.h"

#define CREATE_TRACE_POINTS
#include "trace.h"


/* -- Static controller reference. ------------------------------------------ */

/*
 * Main controller reference. The corresponding lock must be held while
 * accessing (reading/writing) the reference.
 */
static struct ssam_controller *__ssam_controller;
static DEFINE_SPINLOCK(__ssam_controller_lock);

/**
 * ssam_get_controller() - Get reference to SSAM controller.
 *
 * Returns a reference to the SSAM controller of the system or %NULL if there
 * is none, it hasn't been set up yet, or it has already been unregistered.
 * This function automatically increments the reference count of the
 * controller, thus the calling party must ensure that ssam_controller_put()
 * is called when it doesn't need the controller any more.
 */
struct ssam_controller *ssam_get_controller(void)
{
	struct ssam_controller *ctrl;

	spin_lock(&__ssam_controller_lock);

	ctrl = __ssam_controller;
	if (!ctrl)
		goto out;

	if (WARN_ON(!kref_get_unless_zero(&ctrl->kref)))
		ctrl = NULL;

out:
	spin_unlock(&__ssam_controller_lock);
	return ctrl;
}
EXPORT_SYMBOL_GPL(ssam_get_controller);

/**
 * ssam_try_set_controller() - Try to set the main controller reference.
 * @ctrl: The controller to which the reference should point.
 *
 * Set the main controller reference to the given pointer if the reference
 * hasn't been set already.
 *
 * Return: Returns zero on success or %-EEXIST if the reference has already
 * been set.
 */
static int ssam_try_set_controller(struct ssam_controller *ctrl)
{
	int status = 0;

	spin_lock(&__ssam_controller_lock);
	if (!__ssam_controller)
		__ssam_controller = ctrl;
	else
		status = -EEXIST;
	spin_unlock(&__ssam_controller_lock);

	return status;
}

/**
 * ssam_clear_controller() - Remove/clear the main controller reference.
 *
 * Clears the main controller reference, i.e. sets it to %NULL. This function
 * should be called before the controller is shut down.
 */
static void ssam_clear_controller(void)
{
	spin_lock(&__ssam_controller_lock);
	__ssam_controller = NULL;
	spin_unlock(&__ssam_controller_lock);
}

/**
 * ssam_client_link() - Link an arbitrary client device to the controller.
 * @c: The controller to link to.
 * @client: The client device.
 *
 * Link an arbitrary client device to the controller by creating a device link
 * between it as consumer and the controller device as provider. This function
 * can be used for non-SSAM devices (or SSAM devices not registered as child
 * under the controller) to guarantee that the controller is valid for as long
 * as the driver of the client device is bound, and that proper suspend and
 * resume ordering is guaranteed.
 *
 * The device link does not have to be destructed manually. It is removed
 * automatically once the driver of the client device unbinds.
 *
 * Return: Returns zero on success, %-ENODEV if the controller is not ready or
 * going to be removed soon, or %-ENOMEM if the device link could not be
 * created for other reasons.
 */
int ssam_client_link(struct ssam_controller *c, struct device *client)
{
	const u32 flags = DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
	struct device_link *link;
	struct device *ctrldev;

	ssam_controller_statelock(c);

	if (c->state != SSAM_CONTROLLER_STARTED) {
		ssam_controller_stateunlock(c);
		return -ENODEV;
	}

	ctrldev = ssam_controller_device(c);
	if (!ctrldev) {
		ssam_controller_stateunlock(c);
		return -ENODEV;
	}

	link = device_link_add(client, ctrldev, flags);
	if (!link) {
		ssam_controller_stateunlock(c);
		return -ENOMEM;
	}

	/*
	 * Return -ENODEV if supplier driver is on its way to be removed. In
	 * this case, the controller won't be around for much longer and the
	 * device link is not going to save us any more, as unbinding is
	 * already in progress.
	 */
	if (READ_ONCE(link->status) == DL_STATE_SUPPLIER_UNBIND) {
		ssam_controller_stateunlock(c);
		return -ENODEV;
	}

	ssam_controller_stateunlock(c);
	return 0;
}
EXPORT_SYMBOL_GPL(ssam_client_link);

/**
 * ssam_client_bind() - Bind an arbitrary client device to the controller.
 * @client: The client device.
 *
 * Link an arbitrary client device to the controller by creating a device link
 * between it as consumer and the main controller device as provider. This
 * function can be used for non-SSAM devices to guarantee that the controller
 * returned by this function is valid for as long as the driver of the client
 * device is bound, and that proper suspend and resume ordering is guaranteed.
 *
 * This function does essentially the same as ssam_client_link(), except that
 * it first fetches the main controller reference, then creates the link, and
 * finally returns this reference. Note that this function does not increment
 * the reference counter of the controller, as, due to the link, the
 * controller lifetime is assured as long as the driver of the client device
 * is bound.
 *
 * It is not valid to use the controller reference obtained by this method
 * outside of the driver bound to the client device at the time of calling
 * this function, without first incrementing the reference count of the
 * controller via ssam_controller_get(). Even after doing this, care must be
 * taken that requests are only submitted and notifiers are only
 * (un-)registered when the controller is active and not suspended. In other
 * words: The device link only lives as long as the client driver is bound and
 * any guarantees enforced by this link (e.g. active controller state) can
 * only be relied upon as long as this link exists and may need to be enforced
 * in other ways afterwards.
 *
 * The created device link does not have to be destructed manually. It is
 * removed automatically once the driver of the client device unbinds.
 *
 * Return: Returns the controller on success, an error pointer with %-ENODEV
 * if the controller is not present, not ready or going to be removed soon, or
 * %-ENOMEM if the device link could not be created for other reasons.
 */
struct ssam_controller *ssam_client_bind(struct device *client)
{
	struct ssam_controller *c;
	int status;

	c = ssam_get_controller();
	if (!c)
		return ERR_PTR(-ENODEV);

	status = ssam_client_link(c, client);

	/*
	 * Note that we can drop our controller reference in both success and
	 * failure cases: On success, we have bound the controller lifetime
	 * inherently to the client driver lifetime, i.e. it the controller is
	 * now guaranteed to outlive the client driver. On failure, we're not
	 * going to use the controller any more.
	 */
	ssam_controller_put(c);

	return status >= 0 ? c : ERR_PTR(status);
}
EXPORT_SYMBOL_GPL(ssam_client_bind);


/* -- Glue layer (serdev_device -> ssam_controller). ------------------------ */

static int ssam_receive_buf(struct serdev_device *dev, const unsigned char *buf,
			    size_t n)
{
	struct ssam_controller *ctrl;

	ctrl = serdev_device_get_drvdata(dev);
	return ssam_controller_receive_buf(ctrl, buf, n);
}

static void ssam_write_wakeup(struct serdev_device *dev)
{
	ssam_controller_write_wakeup(serdev_device_get_drvdata(dev));
}

static const struct serdev_device_ops ssam_serdev_ops = {
	.receive_buf = ssam_receive_buf,
	.write_wakeup = ssam_write_wakeup,
};


/* -- SysFS and misc. ------------------------------------------------------- */

static int ssam_log_firmware_version(struct ssam_controller *ctrl)
{
	u32 version, a, b, c;
	int status;

	status = ssam_get_firmware_version(ctrl, &version);
	if (status)
		return status;

	a = (version >> 24) & 0xff;
	b = ((version >> 8) & 0xffff);
	c = version & 0xff;

	ssam_info(ctrl, "SAM firmware version: %u.%u.%u\n", a, b, c);
	return 0;
}

static ssize_t firmware_version_show(struct device *dev,
				     struct device_attribute *attr, char *buf)
{
	struct ssam_controller *ctrl = dev_get_drvdata(dev);
	u32 version, a, b, c;
	int status;

	status = ssam_get_firmware_version(ctrl, &version);
	if (status < 0)
		return status;

	a = (version >> 24) & 0xff;
	b = ((version >> 8) & 0xffff);
	c = version & 0xff;

	return sysfs_emit(buf, "%u.%u.%u\n", a, b, c);
}
static DEVICE_ATTR_RO(firmware_version);

static struct attribute *ssam_sam_attrs[] = {
	&dev_attr_firmware_version.attr,
	NULL
};

static const struct attribute_group ssam_sam_group = {
	.name = "sam",
	.attrs = ssam_sam_attrs,
};


/* -- ACPI based device setup. ---------------------------------------------- */

static acpi_status ssam_serdev_setup_via_acpi_crs(struct acpi_resource *rsc,
						  void *ctx)
{
	struct serdev_device *serdev = ctx;
	struct acpi_resource_uart_serialbus *uart;
	bool flow_control;
	int status = 0;

	if (!serdev_acpi_get_uart_resource(rsc, &uart))
		return AE_OK;

	/* Set up serdev device. */
	serdev_device_set_baudrate(serdev, uart->default_baud_rate);

	/* serdev currently only supports RTSCTS flow control. */
	if (uart->flow_control & (~((u8)ACPI_UART_FLOW_CONTROL_HW))) {
		dev_warn(&serdev->dev, "setup: unsupported flow control (value: %#04x)\n",
			 uart->flow_control);
	}

	/* Set RTSCTS flow control. */
	flow_control = uart->flow_control & ACPI_UART_FLOW_CONTROL_HW;
	serdev_device_set_flow_control(serdev, flow_control);

	/* serdev currently only supports EVEN/ODD parity. */
	switch (uart->parity) {
	case ACPI_UART_PARITY_NONE:
		status = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
		break;
	case ACPI_UART_PARITY_EVEN:
		status = serdev_device_set_parity(serdev, SERDEV_PARITY_EVEN);
		break;
	case ACPI_UART_PARITY_ODD:
		status = serdev_device_set_parity(serdev, SERDEV_PARITY_ODD);
		break;
	default:
		dev_warn(&serdev->dev, "setup: unsupported parity (value: %#04x)\n",
			 uart->parity);
		break;
	}

	if (status) {
		dev_err(&serdev->dev, "setup: failed to set parity (value: %#04x, error: %d)\n",
			uart->parity, status);
		return AE_ERROR;
	}

	/* We've found the resource and are done. */
	return AE_CTRL_TERMINATE;
}

static acpi_status ssam_serdev_setup_via_acpi(acpi_handle handle,
					      struct serdev_device *serdev)
{
	return acpi_walk_resources(handle, METHOD_NAME__CRS,
				   ssam_serdev_setup_via_acpi_crs, serdev);
}


/* -- Power management. ----------------------------------------------------- */

static void ssam_serial_hub_shutdown(struct device *dev)
{
	struct ssam_controller *c = dev_get_drvdata(dev);
	int status;

	/*
	 * Try to disable notifiers, signal display-off and D0-exit, ignore any
	 * errors.
	 *
	 * Note: It has not been established yet if this is actually
	 * necessary/useful for shutdown.
	 */

	status = ssam_notifier_disable_registered(c);
	if (status) {
		ssam_err(c, "pm: failed to disable notifiers for shutdown: %d\n",
			 status);
	}

	status = ssam_ctrl_notif_display_off(c);
	if (status)
		ssam_err(c, "pm: display-off notification failed: %d\n", status);

	status = ssam_ctrl_notif_d0_exit(c);
	if (status)
		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
}

#ifdef CONFIG_PM_SLEEP

static int ssam_serial_hub_pm_prepare(struct device *dev)
{
	struct ssam_controller *c = dev_get_drvdata(dev);
	int status;

	/*
	 * Try to signal display-off, This will quiesce events.
	 *
	 * Note: Signaling display-off/display-on should normally be done from
	 * some sort of display state notifier. As that is not available,
	 * signal it here.
	 */

	status = ssam_ctrl_notif_display_off(c);
	if (status)
		ssam_err(c, "pm: display-off notification failed: %d\n", status);

	return status;
}

static void ssam_serial_hub_pm_complete(struct device *dev)
{
	struct ssam_controller *c = dev_get_drvdata(dev);
	int status;

	/*
	 * Try to signal display-on. This will restore events.
	 *
	 * Note: Signaling display-off/display-on should normally be done from
	 * some sort of display state notifier. As that is not available,
	 * signal it here.
	 */

	status = ssam_ctrl_notif_display_on(c);
	if (status)
		ssam_err(c, "pm: display-on notification failed: %d\n", status);
}

static int ssam_serial_hub_pm_suspend(struct device *dev)
{
	struct ssam_controller *c = dev_get_drvdata(dev);
	int status;

	/*
	 * Try to signal D0-exit, enable IRQ wakeup if specified. Abort on
	 * error.
	 */

	status = ssam_ctrl_notif_d0_exit(c);
	if (status) {
		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
		goto err_notif;
	}

	status = ssam_irq_arm_for_wakeup(c);
	if (status)
		goto err_irq;

	WARN_ON(ssam_controller_suspend(c));
	return 0;

err_irq:
	ssam_ctrl_notif_d0_entry(c);
err_notif:
	ssam_ctrl_notif_display_on(c);
	return status;
}

static int ssam_serial_hub_pm_resume(struct device *dev)
{
	struct ssam_controller *c = dev_get_drvdata(dev);
	int status;

	WARN_ON(ssam_controller_resume(c));

	/*
	 * Try to disable IRQ wakeup (if specified) and signal D0-entry. In
	 * case of errors, log them and try to restore normal operation state
	 * as far as possible.
	 *
	 * Note: Signaling display-off/display-on should normally be done from
	 * some sort of display state notifier. As that is not available,
	 * signal it here.
	 */

	ssam_irq_disarm_wakeup(c);

	status = ssam_ctrl_notif_d0_entry(c);
	if (status)
		ssam_err(c, "pm: D0-entry notification failed: %d\n", status);

	return 0;
}

static int ssam_serial_hub_pm_freeze(struct device *dev)
{
	struct ssam_controller *c = dev_get_drvdata(dev);
	int status;

	/*
	 * During hibernation image creation, we only have to ensure that the
	 * EC doesn't send us any events. This is done via the display-off
	 * and D0-exit notifications. Note that this sets up the wakeup IRQ
	 * on the EC side, however, we have disabled it by default on our side
	 * and won't enable it here.
	 *
	 * See ssam_serial_hub_poweroff() for more details on the hibernation
	 * process.
	 */

	status = ssam_ctrl_notif_d0_exit(c);
	if (status) {
		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
		ssam_ctrl_notif_display_on(c);
		return status;
	}

	WARN_ON(ssam_controller_suspend(c));
	return 0;
}

static int ssam_serial_hub_pm_thaw(struct device *dev)
{
	struct ssam_controller *c = dev_get_drvdata(dev);
	int status;

	WARN_ON(ssam_controller_resume(c));

	status = ssam_ctrl_notif_d0_entry(c);
	if (status)
		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);

	return status;
}

static int ssam_serial_hub_pm_poweroff(struct device *dev)
{
	struct ssam_controller *c = dev_get_drvdata(dev);
	int status;

	/*
	 * When entering hibernation and powering off the system, the EC, at
	 * least on some models, may disable events. Without us taking care of
	 * that, this leads to events not being enabled/restored when the
	 * system resumes from hibernation, resulting SAM-HID subsystem devices
	 * (i.e. keyboard, touchpad) not working, AC-plug/AC-unplug events being
	 * gone, etc.
	 *
	 * To avoid these issues, we disable all registered events here (this is
	 * likely not actually required) and restore them during the drivers PM
	 * restore callback.
	 *
	 * Wakeup from the EC interrupt is not supported during hibernation,
	 * so don't arm the IRQ here.
	 */

	status = ssam_notifier_disable_registered(c);
	if (status) {
		ssam_err(c, "pm: failed to disable notifiers for hibernation: %d\n",
			 status);
		return status;
	}

	status = ssam_ctrl_notif_d0_exit(c);
	if (status) {
		ssam_err(c, "pm: D0-exit notification failed: %d\n", status);
		ssam_notifier_restore_registered(c);
		return status;
	}

	WARN_ON(ssam_controller_suspend(c));
	return 0;
}

static int ssam_serial_hub_pm_restore(struct device *dev)
{
	struct ssam_controller *c = dev_get_drvdata(dev);
	int status;

	/*
	 * Ignore but log errors, try to restore state as much as possible in
	 * case of failures. See ssam_serial_hub_poweroff() for more details on
	 * the hibernation process.
	 */

	WARN_ON(ssam_controller_resume(c));

	status = ssam_ctrl_notif_d0_entry(c);
	if (status)
		ssam_err(c, "pm: D0-entry notification failed: %d\n", status);

	ssam_notifier_restore_registered(c);
	return 0;
}

static const struct dev_pm_ops ssam_serial_hub_pm_ops = {
	.prepare  = ssam_serial_hub_pm_prepare,
	.complete = ssam_serial_hub_pm_complete,
	.suspend  = ssam_serial_hub_pm_suspend,
	.resume   = ssam_serial_hub_pm_resume,
	.freeze   = ssam_serial_hub_pm_freeze,
	.thaw     = ssam_serial_hub_pm_thaw,
	.poweroff = ssam_serial_hub_pm_poweroff,
	.restore  = ssam_serial_hub_pm_restore,
};

#else /* CONFIG_PM_SLEEP */

static const struct dev_pm_ops ssam_serial_hub_pm_ops = { };

#endif /* CONFIG_PM_SLEEP */


/* -- Device/driver setup. -------------------------------------------------- */

static const struct acpi_gpio_params gpio_ssam_wakeup_int = { 0, 0, false };
static const struct acpi_gpio_params gpio_ssam_wakeup     = { 1, 0, false };

static const struct acpi_gpio_mapping ssam_acpi_gpios[] = {
	{ "ssam_wakeup-int-gpio", &gpio_ssam_wakeup_int, 1 },
	{ "ssam_wakeup-gpio",     &gpio_ssam_wakeup,     1 },
	{ },
};

static int ssam_serial_hub_probe(struct serdev_device *serdev)
{
	struct acpi_device *ssh = ACPI_COMPANION(&serdev->dev);
	struct ssam_controller *ctrl;
	acpi_status astatus;
	int status;

	if (gpiod_count(&serdev->dev, NULL) < 0)
		return -ENODEV;

	status = devm_acpi_dev_add_driver_gpios(&serdev->dev, ssam_acpi_gpios);
	if (status)
		return status;

	/* Allocate controller. */
	ctrl = kzalloc(sizeof(*ctrl), GFP_KERNEL);
	if (!ctrl)
		return -ENOMEM;

	/* Initialize controller. */
	status = ssam_controller_init(ctrl, serdev);
	if (status)
		goto err_ctrl_init;

	ssam_controller_lock(ctrl);

	/* Set up serdev device. */
	serdev_device_set_drvdata(serdev, ctrl);
	serdev_device_set_client_ops(serdev, &ssam_serdev_ops);
	status = serdev_device_open(serdev);
	if (status)
		goto err_devopen;

	astatus = ssam_serdev_setup_via_acpi(ssh->handle, serdev);
	if (ACPI_FAILURE(astatus)) {
		status = -ENXIO;
		goto err_devinit;
	}

	/* Start controller. */
	status = ssam_controller_start(ctrl);
	if (status)
		goto err_devinit;

	ssam_controller_unlock(ctrl);

	/*
	 * Initial SAM requests: Log version and notify default/init power
	 * states.
	 */
	status = ssam_log_firmware_version(ctrl);
	if (status)
		goto err_initrq;

	status = ssam_ctrl_notif_d0_entry(ctrl);
	if (status)
		goto err_initrq;

	status = ssam_ctrl_notif_display_on(ctrl);
	if (status)
		goto err_initrq;

	status = sysfs_create_group(&serdev->dev.kobj, &ssam_sam_group);
	if (status)
		goto err_initrq;

	/* Set up IRQ. */
	status = ssam_irq_setup(ctrl);
	if (status)
		goto err_irq;

	/* Finally, set main controller reference. */
	status = ssam_try_set_controller(ctrl);
	if (WARN_ON(status))	/* Currently, we're the only provider. */
		goto err_mainref;

	/*
	 * TODO: The EC can wake up the system via the associated GPIO interrupt
	 *       in multiple situations. One of which is the remaining battery
	 *       capacity falling below a certain threshold. Normally, we should
	 *       use the device_init_wakeup function, however, the EC also seems
	 *       to have other reasons for waking up the system and it seems
	 *       that Windows has additional checks whether the system should be
	 *       resumed. In short, this causes some spurious unwanted wake-ups.
	 *       For now let's thus default power/wakeup to false.
	 */
	device_set_wakeup_capable(&serdev->dev, true);
	acpi_dev_clear_dependencies(ssh);

	return 0;

err_mainref:
	ssam_irq_free(ctrl);
err_irq:
	sysfs_remove_group(&serdev->dev.kobj, &ssam_sam_group);
err_initrq:
	ssam_controller_lock(ctrl);
	ssam_controller_shutdown(ctrl);
err_devinit:
	serdev_device_close(serdev);
err_devopen:
	ssam_controller_destroy(ctrl);
	ssam_controller_unlock(ctrl);
err_ctrl_init:
	kfree(ctrl);
	return status;
}

static void ssam_serial_hub_remove(struct serdev_device *serdev)
{
	struct ssam_controller *ctrl = serdev_device_get_drvdata(serdev);
	int status;

	/* Clear static reference so that no one else can get a new one. */
	ssam_clear_controller();

	/* Disable and free IRQ. */
	ssam_irq_free(ctrl);

	sysfs_remove_group(&serdev->dev.kobj, &ssam_sam_group);
	ssam_controller_lock(ctrl);

	/* Remove all client devices. */
	ssam_controller_remove_clients(ctrl);

	/* Act as if suspending to silence events. */
	status = ssam_ctrl_notif_display_off(ctrl);
	if (status) {
		dev_err(&serdev->dev, "display-off notification failed: %d\n",
			status);
	}

	status = ssam_ctrl_notif_d0_exit(ctrl);
	if (status) {
		dev_err(&serdev->dev, "D0-exit notification failed: %d\n",
			status);
	}

	/* Shut down controller and remove serdev device reference from it. */
	ssam_controller_shutdown(ctrl);

	/* Shut down actual transport. */
	serdev_device_wait_until_sent(serdev, 0);
	serdev_device_close(serdev);

	/* Drop our controller reference. */
	ssam_controller_unlock(ctrl);
	ssam_controller_put(ctrl);

	device_set_wakeup_capable(&serdev->dev, false);
}

static const struct acpi_device_id ssam_serial_hub_match[] = {
	{ "MSHW0084", 0 },
	{ },
};
MODULE_DEVICE_TABLE(acpi, ssam_serial_hub_match);

static struct serdev_device_driver ssam_serial_hub = {
	.probe = ssam_serial_hub_probe,
	.remove = ssam_serial_hub_remove,
	.driver = {
		.name = "surface_serial_hub",
		.acpi_match_table = ssam_serial_hub_match,
		.pm = &ssam_serial_hub_pm_ops,
		.shutdown = ssam_serial_hub_shutdown,
		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
	},
};


/* -- Module setup. --------------------------------------------------------- */

static int __init ssam_core_init(void)
{
	int status;

	status = ssam_bus_register();
	if (status)
		goto err_bus;

	status = ssh_ctrl_packet_cache_init();
	if (status)
		goto err_cpkg;

	status = ssam_event_item_cache_init();
	if (status)
		goto err_evitem;

	status = serdev_device_driver_register(&ssam_serial_hub);
	if (status)
		goto err_register;

	return 0;

err_register:
	ssam_event_item_cache_destroy();
err_evitem:
	ssh_ctrl_packet_cache_destroy();
err_cpkg:
	ssam_bus_unregister();
err_bus:
	return status;
}
module_init(ssam_core_init);

static void __exit ssam_core_exit(void)
{
	serdev_device_driver_unregister(&ssam_serial_hub);
	ssam_event_item_cache_destroy();
	ssh_ctrl_packet_cache_destroy();
	ssam_bus_unregister();
}
module_exit(ssam_core_exit);

MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
MODULE_DESCRIPTION("Subsystem and Surface Serial Hub driver for Surface System Aggregator Module");
MODULE_LICENSE("GPL");