OpenCloudOS-Kernel/drivers/hid/intel-ish-hid/ishtp/bus.c

/*
 * ISHTP bus driver
 *
 * Copyright (c) 2012-2016, Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include "bus.h"
#include "ishtp-dev.h"
#include "client.h"
#include "hbm.h"

static int ishtp_use_dma;
module_param_named(ishtp_use_dma, ishtp_use_dma, int, 0600);
MODULE_PARM_DESC(ishtp_use_dma, "Use DMA to send messages");

#define to_ishtp_cl_driver(d) container_of(d, struct ishtp_cl_driver, driver)
#define to_ishtp_cl_device(d) container_of(d, struct ishtp_cl_device, dev)
static bool ishtp_device_ready;

/**
 * ishtp_recv() - process ishtp message
 * @dev: ishtp device
 *
 * If a message with valid header and size is received, then
 * this function calls appropriate handler. The host or firmware
 * address is zero, then they are host bus management message,
 * otherwise they are message fo clients.
 */
void ishtp_recv(struct ishtp_device *dev)
{
	uint32_t	msg_hdr;
	struct ishtp_msg_hdr	*ishtp_hdr;

	/* Read ISHTP header dword */
	msg_hdr = dev->ops->ishtp_read_hdr(dev);
	if (!msg_hdr)
		return;

	dev->ops->sync_fw_clock(dev);

	ishtp_hdr = (struct ishtp_msg_hdr *)&msg_hdr;
	dev->ishtp_msg_hdr = msg_hdr;

	/* Sanity check: ISHTP frag. length in header */
	if (ishtp_hdr->length > dev->mtu) {
		dev_err(dev->devc,
			"ISHTP hdr - bad length: %u; dropped [%08X]\n",
			(unsigned int)ishtp_hdr->length, msg_hdr);
		return;
	}

	/* ISHTP bus message */
	if (!ishtp_hdr->host_addr && !ishtp_hdr->fw_addr)
		recv_hbm(dev, ishtp_hdr);
	/* ISHTP fixed-client message */
	else if (!ishtp_hdr->host_addr)
		recv_fixed_cl_msg(dev, ishtp_hdr);
	else
		/* ISHTP client message */
		recv_ishtp_cl_msg(dev, ishtp_hdr);
}
EXPORT_SYMBOL(ishtp_recv);

/**
 * ishtp_send_msg() - Send ishtp message
 * @dev: ishtp device
 * @hdr: Message header
 * @msg: Message contents
 * @ipc_send_compl: completion callback
 * @ipc_send_compl_prm: completion callback parameter
 *
 * Send a multi fragment message via IPC. After sending the first fragment
 * the completion callback is called to schedule transmit of next fragment.
 *
 * Return: This returns IPC send message status.
 */
int ishtp_send_msg(struct ishtp_device *dev, struct ishtp_msg_hdr *hdr,
		       void *msg, void(*ipc_send_compl)(void *),
		       void *ipc_send_compl_prm)
{
	unsigned char	ipc_msg[IPC_FULL_MSG_SIZE];
	uint32_t	drbl_val;

	drbl_val = dev->ops->ipc_get_header(dev, hdr->length +
					    sizeof(struct ishtp_msg_hdr),
					    1);

	memcpy(ipc_msg, &drbl_val, sizeof(uint32_t));
	memcpy(ipc_msg + sizeof(uint32_t), hdr, sizeof(uint32_t));
	memcpy(ipc_msg + 2 * sizeof(uint32_t), msg, hdr->length);
	return	dev->ops->write(dev, ipc_send_compl, ipc_send_compl_prm,
				ipc_msg, 2 * sizeof(uint32_t) + hdr->length);
}

/**
 * ishtp_write_message() - Send ishtp single fragment message
 * @dev: ishtp device
 * @hdr: Message header
 * @buf: message data
 *
 * Send a single fragment message via IPC.  This returns IPC send message
 * status.
 *
 * Return: This returns IPC send message status.
 */
int ishtp_write_message(struct ishtp_device *dev, struct ishtp_msg_hdr *hdr,
			unsigned char *buf)
{
	return ishtp_send_msg(dev, hdr, buf, NULL, NULL);
}

/**
 * ishtp_fw_cl_by_uuid() - locate index of fw client
 * @dev: ishtp device
 * @uuid: uuid of the client to search
 *
 * Search firmware client using UUID.
 *
 * Return: fw client index or -ENOENT if not found
 */
int ishtp_fw_cl_by_uuid(struct ishtp_device *dev, const uuid_le *uuid)
{
	int i, res = -ENOENT;

	for (i = 0; i < dev->fw_clients_num; ++i) {
		if (uuid_le_cmp(*uuid, dev->fw_clients[i].props.protocol_name)
				== 0) {
			res = i;
			break;
		}
	}
	return res;
}
EXPORT_SYMBOL(ishtp_fw_cl_by_uuid);

/**
 * ishtp_fw_cl_get_client() - return client information to client
 * @dev: the ishtp device structure
 * @uuid: uuid of the client to search
 *
 * Search firmware client using UUID and reture related client information.
 *
 * Return: pointer of client information on success, NULL on failure.
 */
struct ishtp_fw_client *ishtp_fw_cl_get_client(struct ishtp_device *dev,
						const uuid_le *uuid)
{
	int i;
	unsigned long flags;

	spin_lock_irqsave(&dev->fw_clients_lock, flags);
	i = ishtp_fw_cl_by_uuid(dev, uuid);
	spin_unlock_irqrestore(&dev->fw_clients_lock, flags);
	if (i < 0 || dev->fw_clients[i].props.fixed_address)
		return NULL;

	return &dev->fw_clients[i];
}
EXPORT_SYMBOL(ishtp_fw_cl_get_client);

/**
 * ishtp_fw_cl_by_id() - return index to fw_clients for client_id
 * @dev: the ishtp device structure
 * @client_id: fw client id to search
 *
 * Search firmware client using client id.
 *
 * Return: index on success, -ENOENT on failure.
 */
int ishtp_fw_cl_by_id(struct ishtp_device *dev, uint8_t client_id)
{
	int i, res = -ENOENT;
	unsigned long	flags;

	spin_lock_irqsave(&dev->fw_clients_lock, flags);
	for (i = 0; i < dev->fw_clients_num; i++) {
		if (dev->fw_clients[i].client_id == client_id) {
			res = i;
			break;
		}
	}
	spin_unlock_irqrestore(&dev->fw_clients_lock, flags);

	return res;
}

/**
 * ishtp_cl_device_probe() - Bus probe() callback
 * @dev: the device structure
 *
 * This is a bus probe callback and calls the drive probe function.
 *
 * Return: Return value from driver probe() call.
 */
static int ishtp_cl_device_probe(struct device *dev)
{
	struct ishtp_cl_device *device = to_ishtp_cl_device(dev);
	struct ishtp_cl_driver *driver;

	if (!device)
		return 0;

	driver = to_ishtp_cl_driver(dev->driver);
	if (!driver || !driver->probe)
		return -ENODEV;

	return driver->probe(device);
}

/**
 * ishtp_cl_device_remove() - Bus remove() callback
 * @dev: the device structure
 *
 * This is a bus remove callback and calls the drive remove function.
 * Since the ISH driver model supports only built in, this is
 * primarily can be called during pci driver init failure.
 *
 * Return: Return value from driver remove() call.
 */
static int ishtp_cl_device_remove(struct device *dev)
{
	struct ishtp_cl_device *device = to_ishtp_cl_device(dev);
	struct ishtp_cl_driver *driver;

	if (!device || !dev->driver)
		return 0;

	if (device->event_cb) {
		device->event_cb = NULL;
		cancel_work_sync(&device->event_work);
	}

	driver = to_ishtp_cl_driver(dev->driver);
	if (!driver->remove) {
		dev->driver = NULL;

		return 0;
	}

	return driver->remove(device);
}

/**
 * ishtp_cl_device_suspend() - Bus suspend callback
 * @dev:	device
 *
 * Called during device suspend process.
 *
 * Return: Return value from driver suspend() call.
 */
static int ishtp_cl_device_suspend(struct device *dev)
{
	struct ishtp_cl_device *device = to_ishtp_cl_device(dev);
	struct ishtp_cl_driver *driver;
	int ret = 0;

	if (!device)
		return 0;

	driver = to_ishtp_cl_driver(dev->driver);
	if (driver && driver->driver.pm) {
		if (driver->driver.pm->suspend)
			ret = driver->driver.pm->suspend(dev);
	}

	return ret;
}

/**
 * ishtp_cl_device_resume() - Bus resume callback
 * @dev:	device
 *
 * Called during device resume process.
 *
 * Return: Return value from driver resume() call.
 */
static int ishtp_cl_device_resume(struct device *dev)
{
	struct ishtp_cl_device *device = to_ishtp_cl_device(dev);
	struct ishtp_cl_driver *driver;
	int ret = 0;

	if (!device)
		return 0;

	/*
	 * When ISH needs hard reset, it is done asynchrnously, hence bus
	 * resume will  be called before full ISH resume
	 */
	if (device->ishtp_dev->resume_flag)
		return 0;

	driver = to_ishtp_cl_driver(dev->driver);
	if (driver && driver->driver.pm) {
		if (driver->driver.pm->resume)
			ret = driver->driver.pm->resume(dev);
	}

	return ret;
}

/**
 * ishtp_cl_device_reset() - Reset callback
 * @device:	ishtp client device instance
 *
 * This is a callback when HW reset is done and the device need
 * reinit.
 *
 * Return: Return value from driver reset() call.
 */
static int ishtp_cl_device_reset(struct ishtp_cl_device *device)
{
	struct ishtp_cl_driver *driver;
	int ret = 0;

	device->event_cb = NULL;
	cancel_work_sync(&device->event_work);

	driver = to_ishtp_cl_driver(device->dev.driver);
	if (driver && driver->reset)
		ret = driver->reset(device);

	return ret;
}

static ssize_t modalias_show(struct device *dev, struct device_attribute *a,
	char *buf)
{
	int len;

	len = snprintf(buf, PAGE_SIZE, "ishtp:%s\n", dev_name(dev));
	return (len >= PAGE_SIZE) ? (PAGE_SIZE - 1) : len;
}
static DEVICE_ATTR_RO(modalias);

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

static int ishtp_cl_uevent(struct device *dev, struct kobj_uevent_env *env)
{
	if (add_uevent_var(env, "MODALIAS=ishtp:%s", dev_name(dev)))
		return -ENOMEM;
	return 0;
}

static const struct dev_pm_ops ishtp_cl_bus_dev_pm_ops = {
	/* Suspend callbacks */
	.suspend = ishtp_cl_device_suspend,
	.resume = ishtp_cl_device_resume,
	/* Hibernate callbacks */
	.freeze = ishtp_cl_device_suspend,
	.thaw = ishtp_cl_device_resume,
	.restore = ishtp_cl_device_resume,
};

static struct bus_type ishtp_cl_bus_type = {
	.name		= "ishtp",
	.dev_groups	= ishtp_cl_dev_groups,
	.probe		= ishtp_cl_device_probe,
	.remove		= ishtp_cl_device_remove,
	.pm		= &ishtp_cl_bus_dev_pm_ops,
	.uevent		= ishtp_cl_uevent,
};

static void ishtp_cl_dev_release(struct device *dev)
{
	kfree(to_ishtp_cl_device(dev));
}

static const struct device_type ishtp_cl_device_type = {
	.release	= ishtp_cl_dev_release,
};

/**
 * ishtp_bus_add_device() - Function to create device on bus
 * @dev:	ishtp device
 * @uuid:	uuid of the client
 * @name:	Name of the client
 *
 * Allocate ISHTP bus client device, attach it to uuid
 * and register with ISHTP bus.
 *
 * Return: ishtp_cl_device pointer or NULL on failure
 */
static struct ishtp_cl_device *ishtp_bus_add_device(struct ishtp_device *dev,
						    uuid_le uuid, char *name)
{
	struct ishtp_cl_device *device;
	int status;
	unsigned long flags;

	spin_lock_irqsave(&dev->device_list_lock, flags);
	list_for_each_entry(device, &dev->device_list, device_link) {
		if (!strcmp(name, dev_name(&device->dev))) {
			device->fw_client = &dev->fw_clients[
				dev->fw_client_presentation_num - 1];
			spin_unlock_irqrestore(&dev->device_list_lock, flags);
			ishtp_cl_device_reset(device);
			return device;
		}
	}
	spin_unlock_irqrestore(&dev->device_list_lock, flags);

	device = kzalloc(sizeof(struct ishtp_cl_device), GFP_KERNEL);
	if (!device)
		return NULL;

	device->dev.parent = dev->devc;
	device->dev.bus = &ishtp_cl_bus_type;
	device->dev.type = &ishtp_cl_device_type;
	device->ishtp_dev = dev;

	device->fw_client =
		&dev->fw_clients[dev->fw_client_presentation_num - 1];

	dev_set_name(&device->dev, "%s", name);

	spin_lock_irqsave(&dev->device_list_lock, flags);
	list_add_tail(&device->device_link, &dev->device_list);
	spin_unlock_irqrestore(&dev->device_list_lock, flags);

	status = device_register(&device->dev);
	if (status) {
		spin_lock_irqsave(&dev->device_list_lock, flags);
		list_del(&device->device_link);
		spin_unlock_irqrestore(&dev->device_list_lock, flags);
		dev_err(dev->devc, "Failed to register ISHTP client device\n");
		put_device(&device->dev);
		return NULL;
	}

	ishtp_device_ready = true;

	return device;
}

/**
 * ishtp_bus_remove_device() - Function to relase device on bus
 * @device:	client device instance
 *
 * This is a counterpart of ishtp_bus_add_device.
 * Device is unregistered.
 * the device structure is freed in 'ishtp_cl_dev_release' function
 * Called only during error in pci driver init path.
 */
static void ishtp_bus_remove_device(struct ishtp_cl_device *device)
{
	device_unregister(&device->dev);
}

/**
 * __ishtp_cl_driver_register() - Client driver register
 * @driver:	the client driver instance
 * @owner:	Owner of this driver module
 *
 * Once a client driver is probed, it created a client
 * instance and registers with the bus.
 *
 * Return: Return value of driver_register or -ENODEV if not ready
 */
int __ishtp_cl_driver_register(struct ishtp_cl_driver *driver,
			       struct module *owner)
{
	int err;

	if (!ishtp_device_ready)
		return -ENODEV;

	driver->driver.name = driver->name;
	driver->driver.owner = owner;
	driver->driver.bus = &ishtp_cl_bus_type;

	err = driver_register(&driver->driver);
	if (err)
		return err;

	return 0;
}
EXPORT_SYMBOL(__ishtp_cl_driver_register);

/**
 * ishtp_cl_driver_unregister() - Client driver unregister
 * @driver:	the client driver instance
 *
 * Unregister client during device removal process.
 */
void ishtp_cl_driver_unregister(struct ishtp_cl_driver *driver)
{
	driver_unregister(&driver->driver);
}
EXPORT_SYMBOL(ishtp_cl_driver_unregister);

/**
 * ishtp_bus_event_work() - event work function
 * @work:	work struct pointer
 *
 * Once an event is received for a client this work
 * function is called. If the device has registered a
 * callback then the callback is called.
 */
static void ishtp_bus_event_work(struct work_struct *work)
{
	struct ishtp_cl_device *device;

	device = container_of(work, struct ishtp_cl_device, event_work);

	if (device->event_cb)
		device->event_cb(device);
}

/**
 * ishtp_cl_bus_rx_event() - schedule event work
 * @device:	client device instance
 *
 * Once an event is received for a client this schedules
 * a work function to process.
 */
void ishtp_cl_bus_rx_event(struct ishtp_cl_device *device)
{
	if (!device || !device->event_cb)
		return;

	if (device->event_cb)
		schedule_work(&device->event_work);
}

/**
 * ishtp_register_event_cb() - Register callback
 * @device:	client device instance
 * @event_cb:	Event processor for an client
 *
 * Register a callback for events, called from client driver
 *
 * Return: Return 0 or -EALREADY if already registered
 */
int ishtp_register_event_cb(struct ishtp_cl_device *device,
	void (*event_cb)(struct ishtp_cl_device *))
{
	if (device->event_cb)
		return -EALREADY;

	device->event_cb = event_cb;
	INIT_WORK(&device->event_work, ishtp_bus_event_work);

	return 0;
}
EXPORT_SYMBOL(ishtp_register_event_cb);

/**
 * ishtp_get_device() - update usage count for the device
 * @cl_device:	client device instance
 *
 * Increment the usage count. The device can't be deleted
 */
void ishtp_get_device(struct ishtp_cl_device *cl_device)
{
	cl_device->reference_count++;
}
EXPORT_SYMBOL(ishtp_get_device);

/**
 * ishtp_put_device() - decrement usage count for the device
 * @cl_device:	client device instance
 *
 * Decrement the usage count. The device can be deleted is count = 0
 */
void ishtp_put_device(struct ishtp_cl_device *cl_device)
{
	cl_device->reference_count--;
}
EXPORT_SYMBOL(ishtp_put_device);

/**
 * ishtp_set_drvdata() - set client driver data
 * @cl_device:	client device instance
 * @data:	driver data need to be set
 *
 * Set client driver data to cl_device->driver_data.
 */
void ishtp_set_drvdata(struct ishtp_cl_device *cl_device, void *data)
{
	cl_device->driver_data = data;
}
EXPORT_SYMBOL(ishtp_set_drvdata);

/**
 * ishtp_get_drvdata() - get client driver data
 * @cl_device:	client device instance
 *
 * Get client driver data from cl_device->driver_data.
 *
 * Return: pointer of driver data
 */
void *ishtp_get_drvdata(struct ishtp_cl_device *cl_device)
{
	return cl_device->driver_data;
}
EXPORT_SYMBOL(ishtp_get_drvdata);

/**
 * ishtp_bus_new_client() - Create a new client
 * @dev:	ISHTP device instance
 *
 * Once bus protocol enumerates a client, this is called
 * to add a device for the client.
 *
 * Return: 0 on success or error code on failure
 */
int ishtp_bus_new_client(struct ishtp_device *dev)
{
	int	i;
	char	*dev_name;
	struct ishtp_cl_device	*cl_device;
	uuid_le	device_uuid;

	/*
	 * For all reported clients, create an unconnected client and add its
	 * device to ISHTP bus.
	 * If appropriate driver has loaded, this will trigger its probe().
	 * Otherwise, probe() will be called when driver is loaded
	 */
	i = dev->fw_client_presentation_num - 1;
	device_uuid = dev->fw_clients[i].props.protocol_name;
	dev_name = kasprintf(GFP_KERNEL, "{%pUL}", device_uuid.b);
	if (!dev_name)
		return	-ENOMEM;

	cl_device = ishtp_bus_add_device(dev, device_uuid, dev_name);
	if (!cl_device) {
		kfree(dev_name);
		return	-ENOENT;
	}

	kfree(dev_name);

	return	0;
}

/**
 * ishtp_cl_device_bind() - bind a device
 * @cl:		ishtp client device
 *
 * Binds connected ishtp_cl to ISHTP bus device
 *
 * Return: 0 on success or fault code
 */
int ishtp_cl_device_bind(struct ishtp_cl *cl)
{
	struct ishtp_cl_device	*cl_device;
	unsigned long flags;
	int	rv;

	if (!cl->fw_client_id || cl->state != ISHTP_CL_CONNECTED)
		return	-EFAULT;

	rv = -ENOENT;
	spin_lock_irqsave(&cl->dev->device_list_lock, flags);
	list_for_each_entry(cl_device, &cl->dev->device_list,
			device_link) {
		if (cl_device->fw_client &&
		    cl_device->fw_client->client_id == cl->fw_client_id) {
			cl->device = cl_device;
			rv = 0;
			break;
		}
	}
	spin_unlock_irqrestore(&cl->dev->device_list_lock, flags);
	return	rv;
}

/**
 * ishtp_bus_remove_all_clients() - Remove all clients
 * @ishtp_dev:		ishtp device
 * @warm_reset:		Reset due to FW reset dure to errors or S3 suspend
 *
 * This is part of reset/remove flow. This function the main processing
 * only targets error processing, if the FW has forced reset or
 * error to remove connected clients. When warm reset the client devices are
 * not removed.
 */
void ishtp_bus_remove_all_clients(struct ishtp_device *ishtp_dev,
				  bool warm_reset)
{
	struct ishtp_cl_device	*cl_device, *n;
	struct ishtp_cl	*cl;
	unsigned long	flags;

	spin_lock_irqsave(&ishtp_dev->cl_list_lock, flags);
	list_for_each_entry(cl, &ishtp_dev->cl_list, link) {
		cl->state = ISHTP_CL_DISCONNECTED;

		/*
		 * Wake any pending process. The waiter would check dev->state
		 * and determine that it's not enabled already,
		 * and will return error to its caller
		 */
		wake_up_interruptible(&cl->wait_ctrl_res);

		/* Disband any pending read/write requests and free rb */
		ishtp_cl_flush_queues(cl);

		/* Remove all free and in_process rings, both Rx and Tx */
		ishtp_cl_free_rx_ring(cl);
		ishtp_cl_free_tx_ring(cl);

		/*
		 * Free client and ISHTP bus client device structures
		 * don't free host client because it is part of the OS fd
		 * structure
		 */
	}
	spin_unlock_irqrestore(&ishtp_dev->cl_list_lock, flags);

	/* Release DMA buffers for client messages */
	ishtp_cl_free_dma_buf(ishtp_dev);

	/* remove bus clients */
	spin_lock_irqsave(&ishtp_dev->device_list_lock, flags);
	list_for_each_entry_safe(cl_device, n, &ishtp_dev->device_list,
				 device_link) {
		cl_device->fw_client = NULL;
		if (warm_reset && cl_device->reference_count)
			continue;

		list_del(&cl_device->device_link);
		spin_unlock_irqrestore(&ishtp_dev->device_list_lock, flags);
		ishtp_bus_remove_device(cl_device);
		spin_lock_irqsave(&ishtp_dev->device_list_lock, flags);
	}
	spin_unlock_irqrestore(&ishtp_dev->device_list_lock, flags);

	/* Free all client structures */
	spin_lock_irqsave(&ishtp_dev->fw_clients_lock, flags);
	kfree(ishtp_dev->fw_clients);
	ishtp_dev->fw_clients = NULL;
	ishtp_dev->fw_clients_num = 0;
	ishtp_dev->fw_client_presentation_num = 0;
	ishtp_dev->fw_client_index = 0;
	bitmap_zero(ishtp_dev->fw_clients_map, ISHTP_CLIENTS_MAX);
	spin_unlock_irqrestore(&ishtp_dev->fw_clients_lock, flags);
}
EXPORT_SYMBOL(ishtp_bus_remove_all_clients);

/**
 * ishtp_reset_handler() - IPC reset handler
 * @dev:	ishtp device
 *
 * ISHTP Handler for IPC_RESET notification
 */
void ishtp_reset_handler(struct ishtp_device *dev)
{
	unsigned long	flags;

	/* Handle FW-initiated reset */
	dev->dev_state = ISHTP_DEV_RESETTING;

	/* Clear BH processing queue - no further HBMs */
	spin_lock_irqsave(&dev->rd_msg_spinlock, flags);
	dev->rd_msg_fifo_head = dev->rd_msg_fifo_tail = 0;
	spin_unlock_irqrestore(&dev->rd_msg_spinlock, flags);

	/* Handle ISH FW reset against upper layers */
	ishtp_bus_remove_all_clients(dev, true);
}
EXPORT_SYMBOL(ishtp_reset_handler);

/**
 * ishtp_reset_compl_handler() - Reset completion handler
 * @dev:	ishtp device
 *
 * ISHTP handler for IPC_RESET sequence completion to start
 * host message bus start protocol sequence.
 */
void ishtp_reset_compl_handler(struct ishtp_device *dev)
{
	dev->dev_state = ISHTP_DEV_INIT_CLIENTS;
	dev->hbm_state = ISHTP_HBM_START;
	ishtp_hbm_start_req(dev);
}
EXPORT_SYMBOL(ishtp_reset_compl_handler);

/**
 * ishtp_use_dma_transfer() - Function to use DMA
 *
 * This interface is used to enable usage of DMA
 *
 * Return non zero if DMA can be enabled
 */
int ishtp_use_dma_transfer(void)
{
	return ishtp_use_dma;
}

/**
 * ishtp_bus_register() - Function to register bus
 *
 * This register ishtp bus
 *
 * Return: Return output of bus_register
 */
static int  __init ishtp_bus_register(void)
{
	return bus_register(&ishtp_cl_bus_type);
}

/**
 * ishtp_bus_unregister() - Function to unregister bus
 *
 * This unregister ishtp bus
 */
static void __exit ishtp_bus_unregister(void)
{
	bus_unregister(&ishtp_cl_bus_type);
}

module_init(ishtp_bus_register);
module_exit(ishtp_bus_unregister);

MODULE_LICENSE("GPL");