[PATCH] bus: mhi: host: Add userspace character interface

[Jeffrey Hugo]

From: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@xxxxxxxxxxx>

I2C, USB, and PCIe are examples of buses which have a mechanism to give
userspace direct access to a device on those buses. The MHI userspace
character interface (uci) is the MHI bus analogue.

The MHI bus devices are MHI channels which ferry blocks of data from one
end to the other. With this simple purpose, we can define a simple
interface to userspace - a character device that supports open/close/read/
write/poll operations. Since bus devices can only have a single consumer
we encode a whitelist of MHI channels to be exported to userspace so as
to avoid conflicts.

We also make this mechanism open to any device that implements MHI.
Today this includes WLAN (Wi-Fi), WWAN (4G/5G cellular), and ML/AI
devices. More devices are expected in the future.

In addition to implementing the framework for uci, we include an initial
usecase - the QAIC Sahara device.

Sahara is a file transfer protocol that is commonly used for two purposes
when interacting with a device - transferring firmware to the device and
transferring crashdumps from the device. The Sahara protocol puts the
receiver of the data in control of the transfer. A firmware transfer
operation would have the device requesting the specific firmware images
that the device wants, and the host satisfying those requests.

In most cases, including for AIC100, Sahara is used as part of a two stage
loading process. The device will boot a very limited bootloader that does
the base minimum initialization and jump to the next stage. A simple, one-
shot protocol like BHI is used to send the next stage bootloader to the
device. This second stage bootloader contains more functionality and
implements the Sahara protocol. The second stage determines from various
inputs what set of runtime firmware is required to boot the device into an
operational status, and requests those pieces from the host.  With those
images transferred over, the device can funnly initialize.

Each AIC100 instance (currently, up to 16) in a system will create a
MHI device for QAIC_SAHARA. MHI_uci will consume each of these and create
a unique chardev which will be found as
/dev/<mhi instance>_QAIC_SAHARA
For example - /dev/mhi0_QAIC_SAHARA

An open userspace application that can consume these devices for firmware
transfers is located at https://github.com/andersson/qdl

Signed-off-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@xxxxxxxxxxx>
[jhugo: Rename to uci, plumb to mhi, rewrite commit text]
Signed-off-by: Jeffrey Hugo <quic_jhugo@xxxxxxxxxxx>
---

Previous uci proposal - https://lore.kernel.org/all/1609958656-15064-1-git-send-email-hemantk@xxxxxxxxxxxxxx/

 drivers/bus/mhi/host/Makefile   |   2 +-
 drivers/bus/mhi/host/init.c     |  13 +-
 drivers/bus/mhi/host/internal.h |   4 +
 drivers/bus/mhi/host/uci.c      | 566 ++++++++++++++++++++++++++++++++
 4 files changed, 583 insertions(+), 2 deletions(-)
 create mode 100644 drivers/bus/mhi/host/uci.c

diff --git a/drivers/bus/mhi/host/Makefile b/drivers/bus/mhi/host/Makefile
index 859c2f38451c..7e446355680b 100644
--- a/drivers/bus/mhi/host/Makefile
+++ b/drivers/bus/mhi/host/Makefile
@@ -1,5 +1,5 @@
 obj-$(CONFIG_MHI_BUS) += mhi.o
-mhi-y := init.o main.o pm.o boot.o
+mhi-y := init.o main.o pm.o boot.o uci.o
 mhi-$(CONFIG_MHI_BUS_DEBUG) += debugfs.o
 
 obj-$(CONFIG_MHI_BUS_PCI_GENERIC) += mhi_pci_generic.o
diff --git a/drivers/bus/mhi/host/init.c b/drivers/bus/mhi/host/init.c
index f72fcb66f408..ed4b345d8222 100644
--- a/drivers/bus/mhi/host/init.c
+++ b/drivers/bus/mhi/host/init.c
@@ -1447,13 +1447,24 @@ struct bus_type mhi_bus_type = {
 
 static int __init mhi_init(void)
 {
+	int ret;
+
 	mhi_debugfs_init();
-	return bus_register(&mhi_bus_type);
+	ret = bus_register(&mhi_bus_type);
+	if (ret)
+		return ret;
+
+	ret = mhi_uci_init();
+	if (ret)
+		bus_unregister(&mhi_bus_type);
+
+	return ret;
 }
 
 static void __exit mhi_exit(void)
 {
 	mhi_debugfs_exit();
+	mhi_uci_exit();
 	bus_unregister(&mhi_bus_type);
 }
 
diff --git a/drivers/bus/mhi/host/internal.h b/drivers/bus/mhi/host/internal.h
index 2e139e76de4c..52ddaaab81fc 100644
--- a/drivers/bus/mhi/host/internal.h
+++ b/drivers/bus/mhi/host/internal.h
@@ -380,4 +380,8 @@ void mhi_unmap_single_no_bb(struct mhi_controller *mhi_cntrl,
 void mhi_unmap_single_use_bb(struct mhi_controller *mhi_cntrl,
 			     struct mhi_buf_info *buf_info);
 
+/* UCI hooks */
+int mhi_uci_init(void);
+void mhi_uci_exit(void);
+
 #endif /* _MHI_INT_H */
diff --git a/drivers/bus/mhi/host/uci.c b/drivers/bus/mhi/host/uci.c
new file mode 100644
index 000000000000..e67fc6f7d8db
--- /dev/null
+++ b/drivers/bus/mhi/host/uci.c
@@ -0,0 +1,566 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved. */
+
+#include <linux/kernel.h>
+#include <linux/mhi.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/poll.h>
+#include <linux/xarray.h>
+#include <uapi/linux/eventpoll.h>
+
+#define MHI_UCI_DRIVER_NAME		"mhi_uci"
+#define MHI_UCI_MAX_MINORS		128
+#define MHI_MAX_MTU			0xffff
+static DEFINE_XARRAY_ALLOC(uci_xa);
+static struct class *uci_dev_class;
+static int uci_dev_major;
+
+/**
+ * struct uci_buf - Buffer structure used to receive data from device
+ * @data: Address of data to read from
+ * @odata: Original address returned from *alloc() API. Used to free this buf.
+ * @len: Length of data in byte
+ * @node: This buffer will be part of list managed in struct uci_dev
+ */
+struct uci_buf {
+	void *data;
+	void *odata;
+	size_t len;
+	struct list_head node;
+};
+
+/**
+ * struct uci_dev - MHI UCI Device
+ * @minor: uci device node minor number
+ * @mhi_dev: Associated mhi device object
+ * @mtu: Max TRE buffer length
+ * @enabled: Flag to track the state of the uci device
+ * @lock: Mutex lock to serialize access to open_count
+ * @read_lock: Mutex lock to serialize readers
+ * @write_lock: Mutex lock to serialize writers
+ * @ul_wq: Wait queue for writers
+ * @dl_wq: Wait queue for readers
+ * @dl_queue_lock: Spin lock to serialize access to download queue
+ * @dl_queue: Queue of downloaded buffers
+ * @open_count: Track open counts
+ * @ref_count: Reference count for this structure
+ */
+struct uci_dev {
+	uint32_t minor;
+	struct mhi_device *mhi_dev;
+	size_t mtu;
+	bool enabled;
+	struct mutex lock;
+	struct mutex read_lock;
+	struct mutex write_lock;
+	wait_queue_head_t ul_wq;
+	wait_queue_head_t dl_wq;
+	spinlock_t dl_queue_lock;
+	struct list_head dl_queue;
+	unsigned int open_count;
+	struct kref ref_count;
+};
+
+static void uci_dev_release(struct kref *ref)
+{
+	struct uci_dev *ucidev = container_of(ref, struct uci_dev, ref_count);
+
+	mutex_destroy(&ucidev->read_lock);
+	mutex_destroy(&ucidev->write_lock);
+	mutex_destroy(&ucidev->lock);
+	kfree(ucidev);
+}
+
+static int mhi_uci_fill_dl_queue(struct uci_dev *ucidev)
+{
+	struct mhi_device *mhi_dev = ucidev->mhi_dev;
+	struct uci_buf *ucibuf;
+	int rx_budget;
+	int ret = 0;
+	void *data;
+
+	rx_budget = mhi_get_free_desc_count(mhi_dev, DMA_FROM_DEVICE);
+	if (rx_budget < 0)
+		return -EIO;
+
+	while (rx_budget--) {
+		data = kzalloc(ucidev->mtu + sizeof(*ucibuf), GFP_KERNEL);
+		if (!data)
+			return -ENOMEM;
+
+		ucibuf = data + ucidev->mtu;
+		ucibuf->odata = data;
+
+		ret = mhi_queue_buf(mhi_dev, DMA_FROM_DEVICE, data, ucidev->mtu, MHI_EOT);
+		if (ret) {
+			kfree(data);
+			dev_err(&mhi_dev->dev, "Failed to queue buffer\n");
+			return ret;
+		}
+	}
+
+	return ret;
+}
+
+static int mhi_uci_dev_start_chan(struct uci_dev *ucidev)
+{
+	struct device *dev = &ucidev->mhi_dev->dev;
+	int ret = 0;
+
+	ret = mutex_lock_interruptible(&ucidev->lock);
+	if (ret)
+		return ret;
+	if (!ucidev->enabled) {
+		ret = -ENODEV;
+		goto release_dev_lock;
+	}
+	if (!ucidev->open_count) {
+		ret = mhi_prepare_for_transfer(ucidev->mhi_dev);
+		if (ret) {
+			dev_err(dev, "Error starting transfer channels\n");
+			goto release_dev_lock;
+		}
+
+		ret = mhi_uci_fill_dl_queue(ucidev);
+		if (ret) {
+			dev_err(dev, "Error filling download queue.\n");
+			goto mhi_unprepare;
+		}
+	}
+	ucidev->open_count++;
+	mutex_unlock(&ucidev->lock);
+
+	return 0;
+
+mhi_unprepare:
+	mhi_unprepare_from_transfer(ucidev->mhi_dev);
+release_dev_lock:
+	mutex_unlock(&ucidev->lock);
+	return ret;
+}
+
+static struct uci_dev *uci_dev_get_by_minor(unsigned int minor)
+{
+	struct uci_dev *ucidev;
+
+	xa_lock(&uci_xa);
+	ucidev = xa_load(&uci_xa, minor);
+	if (ucidev)
+		kref_get(&ucidev->ref_count);
+	xa_unlock(&uci_xa);
+
+	return ucidev;
+}
+
+static int mhi_uci_open(struct inode *inode, struct file *filp)
+{
+	struct uci_dev *ucidev;
+	int ret;
+
+	ucidev = uci_dev_get_by_minor(iminor(inode));
+	if (!ucidev) {
+		pr_debug("mqc: minor %d not found\n", iminor(inode));
+		return -EINVAL;
+	}
+
+	ret = mhi_uci_dev_start_chan(ucidev);
+	if (ret) {
+		kref_put(&ucidev->ref_count, uci_dev_release);
+		return ret;
+	}
+
+	filp->private_data = ucidev;
+
+	return 0;
+}
+
+static void mhi_uci_buf_free(struct uci_buf *ucibuf)
+{
+	list_del(&ucibuf->node);
+	kfree(ucibuf->odata);
+}
+
+static void __mhi_uci_release(struct uci_dev *ucidev)
+{
+	struct uci_buf *ucibuf, *tmp;
+
+	mhi_unprepare_from_transfer(ucidev->mhi_dev);
+	wake_up_interruptible(&ucidev->ul_wq);
+	wake_up_interruptible(&ucidev->dl_wq);
+	/*
+	 * Free the dl_queue. As we have already unprepared mhi transfers, we
+	 * do not expect any callback functions that update dl_queue hence no need
+	 * to grab dl_queue lock.
+	 */
+	mutex_lock(&ucidev->read_lock);
+	list_for_each_entry_safe(ucibuf, tmp, &ucidev->dl_queue, node)
+		mhi_uci_buf_free(ucibuf);
+	mutex_unlock(&ucidev->read_lock);
+}
+
+static int mhi_uci_release(struct inode *inode, struct file *file)
+{
+	struct uci_dev *ucidev = file->private_data;
+
+	mutex_lock(&ucidev->lock);
+	ucidev->open_count--;
+	if (!ucidev->open_count && ucidev->enabled)
+		__mhi_uci_release(ucidev);
+	mutex_unlock(&ucidev->lock);
+
+	kref_put(&ucidev->ref_count, uci_dev_release);
+
+	return 0;
+}
+
+static __poll_t mhi_uci_poll(struct file *file, poll_table *wait)
+{
+	struct uci_dev *ucidev = file->private_data;
+	struct mhi_device *mhi_dev;
+	__poll_t mask = 0;
+
+	mhi_dev = ucidev->mhi_dev;
+
+	poll_wait(file, &ucidev->ul_wq, wait);
+	poll_wait(file, &ucidev->dl_wq, wait);
+
+	mutex_lock(&ucidev->lock);
+	if (!ucidev->enabled) {
+		mutex_unlock(&ucidev->lock);
+		return EPOLLERR;
+	}
+
+	spin_lock_bh(&ucidev->dl_queue_lock);
+	if (!list_empty(&ucidev->dl_queue))
+		mask |= EPOLLIN | EPOLLRDNORM;
+	spin_unlock_bh(&ucidev->dl_queue_lock);
+
+	if (mutex_lock_interruptible(&ucidev->write_lock)) {
+		mutex_unlock(&ucidev->lock);
+		return EPOLLERR;
+	}
+	if (mhi_get_free_desc_count(mhi_dev, DMA_TO_DEVICE) > 0)
+		mask |= EPOLLOUT | EPOLLWRNORM;
+	mutex_unlock(&ucidev->write_lock);
+	mutex_unlock(&ucidev->lock);
+
+	dev_dbg(&mhi_dev->dev, "Client attempted to poll, returning mask 0x%x\n", mask);
+
+	return mask;
+}
+
+static int mhi_uci_tx(struct uci_dev *ucidev)
+{
+	int ret;
+
+	ret = wait_event_interruptible(ucidev->ul_wq, (!ucidev->enabled ||
+				       mhi_get_free_desc_count(ucidev->mhi_dev,
+							       DMA_TO_DEVICE) > 0));
+
+	if (!ucidev->enabled)
+		return -ENODEV;
+
+	return ret;
+}
+
+static ssize_t mhi_uci_write(struct file *file, const char __user *buf, size_t count, loff_t *offp)
+{
+	struct uci_dev *ucidev = file->private_data;
+	struct mhi_device *mhi_dev;
+	size_t bytes_xfered = 0;
+	struct device *dev;
+	int ret, nr_desc;
+
+	mhi_dev = ucidev->mhi_dev;
+	dev = &mhi_dev->dev;
+
+	if (!mhi_dev->ul_chan)
+		return -EOPNOTSUPP;
+
+	if (!buf || !count)
+		return -EINVAL;
+
+	dev_dbg(dev, "Request to transfer %zu bytes\n", count);
+
+	ret = mhi_uci_tx(ucidev);
+	if (ret)
+		return ret;
+
+	if (mutex_lock_interruptible(&ucidev->write_lock))
+		return -EINTR;
+
+	nr_desc = mhi_get_free_desc_count(mhi_dev, DMA_TO_DEVICE);
+	if (nr_desc * ucidev->mtu < count) {
+		ret = -EMSGSIZE;
+		dev_dbg(dev, "Buffer too big to transfer\n");
+		goto unlock_mutex;
+	}
+
+	while (count != bytes_xfered) {
+		enum mhi_flags flags;
+		size_t to_copy;
+		void *kbuf;
+
+		to_copy = min_t(size_t, count - bytes_xfered, ucidev->mtu);
+		kbuf = kmalloc(to_copy, GFP_KERNEL);
+		if (!kbuf) {
+			ret = -ENOMEM;
+			goto unlock_mutex;
+		}
+
+		ret = copy_from_user(kbuf, buf + bytes_xfered, to_copy);
+		if (ret) {
+			kfree(kbuf);
+			ret = -EFAULT;
+			goto unlock_mutex;
+		}
+
+		if (bytes_xfered + to_copy == count)
+			flags = MHI_EOT;
+		else
+			flags = MHI_CHAIN;
+
+		ret = mhi_queue_buf(mhi_dev, DMA_TO_DEVICE, kbuf, to_copy, flags);
+		if (ret) {
+			kfree(kbuf);
+			dev_err(dev, "Failed to queue buf of size %zu\n", to_copy);
+			goto unlock_mutex;
+		}
+
+		bytes_xfered += to_copy;
+	}
+
+	mutex_unlock(&ucidev->write_lock);
+	dev_dbg(dev, "bytes xferred: %zu\n", bytes_xfered);
+
+	return bytes_xfered;
+
+unlock_mutex:
+	mutex_unlock(&ucidev->write_lock);
+	return ret;
+}
+
+static int mhi_uci_rx(struct uci_dev *ucidev)
+{
+	int ret;
+
+	ret = wait_event_interruptible(ucidev->dl_wq, (!ucidev->enabled ||
+				       !list_empty(&ucidev->dl_queue)));
+
+	if (!ucidev->enabled)
+		return -ENODEV;
+
+	return ret;
+}
+
+static ssize_t mhi_uci_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
+{
+	struct uci_dev *ucidev = file->private_data;
+	struct uci_buf *ucibuf;
+	size_t to_copy;
+	int ret;
+
+	if (!ucidev->mhi_dev->dl_chan)
+		return -EOPNOTSUPP;
+
+	ret = mhi_uci_rx(ucidev);
+	if (ret)
+		return ret;
+
+	if (mutex_lock_interruptible(&ucidev->read_lock))
+		return -EINTR;
+
+	ucibuf = list_first_entry_or_null(&ucidev->dl_queue, struct uci_buf, node);
+	if (!ucibuf) {
+		mutex_unlock(&ucidev->read_lock);
+		ret = -ENODEV;
+		goto error_out;
+	}
+
+	to_copy = min_t(size_t, count, ucibuf->len);
+	if (copy_to_user(buf, ucibuf->data, to_copy)) {
+		mutex_unlock(&ucidev->read_lock);
+		dev_dbg(&ucidev->mhi_dev->dev, "Failed to copy data to user buffer\n");
+		ret = -EFAULT;
+		goto error_out;
+	}
+
+	ucibuf->len -= to_copy;
+	ucibuf->data += to_copy;
+
+	if (!ucibuf->len) {
+		spin_lock_bh(&ucidev->dl_queue_lock);
+		mhi_uci_buf_free(ucibuf);
+		spin_unlock_bh(&ucidev->dl_queue_lock);
+		mhi_uci_fill_dl_queue(ucidev);
+		dev_dbg(&ucidev->mhi_dev->dev, "Read buf freed\n");
+	}
+
+	mutex_unlock(&ucidev->read_lock);
+	return to_copy;
+
+error_out:
+	mutex_unlock(&ucidev->read_lock);
+	return ret;
+}
+
+static const struct file_operations mhidev_fops = {
+	.owner = THIS_MODULE,
+	.open = mhi_uci_open,
+	.release = mhi_uci_release,
+	.read = mhi_uci_read,
+	.write = mhi_uci_write,
+	.poll = mhi_uci_poll,
+};
+
+static void mhi_uci_ul_xfer_cb(struct mhi_device *mhi_dev, struct mhi_result *mhi_result)
+{
+	struct uci_dev *ucidev = dev_get_drvdata(&mhi_dev->dev);
+
+	dev_dbg(&mhi_dev->dev, "%s: status: %d xfer_len: %zu\n", __func__,
+		mhi_result->transaction_status, mhi_result->bytes_xferd);
+
+	kfree(mhi_result->buf_addr);
+
+	if (!mhi_result->transaction_status)
+		wake_up_interruptible(&ucidev->ul_wq);
+}
+
+static void mhi_uci_dl_xfer_cb(struct mhi_device *mhi_dev, struct mhi_result *mhi_result)
+{
+	struct uci_dev *ucidev = dev_get_drvdata(&mhi_dev->dev);
+	struct uci_buf *ucibuf;
+
+	dev_dbg(&mhi_dev->dev, "%s: status: %d receive_len: %zu\n", __func__,
+		mhi_result->transaction_status, mhi_result->bytes_xferd);
+
+	if (mhi_result->transaction_status &&
+	    mhi_result->transaction_status != -EOVERFLOW) {
+		kfree(mhi_result->buf_addr);
+		return;
+	}
+
+	ucibuf = mhi_result->buf_addr + ucidev->mtu;
+	ucibuf->data = mhi_result->buf_addr;
+	ucibuf->len = mhi_result->bytes_xferd;
+	spin_lock_bh(&ucidev->dl_queue_lock);
+	list_add_tail(&ucibuf->node, &ucidev->dl_queue);
+	spin_unlock_bh(&ucidev->dl_queue_lock);
+
+	wake_up_interruptible(&ucidev->dl_wq);
+}
+
+static int mhi_uci_probe(struct mhi_device *mhi_dev, const struct mhi_device_id *id)
+{
+	struct uci_dev *ucidev;
+	struct device *dev;
+	int ret;
+
+	ucidev = kzalloc(sizeof(*ucidev), GFP_KERNEL);
+	if (!ucidev)
+		return -ENOMEM;
+
+	kref_init(&ucidev->ref_count);
+	mutex_init(&ucidev->lock);
+	ucidev->mhi_dev = mhi_dev;
+
+	ret = xa_alloc(&uci_xa, &ucidev->minor, ucidev, XA_LIMIT(0, MHI_UCI_MAX_MINORS),
+		       GFP_KERNEL);
+	if (ret) {
+		kfree(ucidev);
+		return ret;
+	}
+
+	init_waitqueue_head(&ucidev->ul_wq);
+	init_waitqueue_head(&ucidev->dl_wq);
+	mutex_init(&ucidev->read_lock);
+	mutex_init(&ucidev->write_lock);
+	spin_lock_init(&ucidev->dl_queue_lock);
+	INIT_LIST_HEAD(&ucidev->dl_queue);
+	ucidev->mtu = min_t(size_t, id->driver_data, MHI_MAX_MTU);
+	ucidev->enabled = true;
+	ucidev->open_count = 0;
+	dev_set_drvdata(&mhi_dev->dev, ucidev);
+
+	dev = device_create(uci_dev_class, &mhi_dev->dev, MKDEV(uci_dev_major, ucidev->minor),
+			    ucidev, "%s", dev_name(&mhi_dev->dev));
+	if (IS_ERR(dev)) {
+		xa_erase(&uci_xa, ucidev->minor);
+		dev_set_drvdata(&mhi_dev->dev, NULL);
+		kfree(ucidev);
+		return PTR_ERR(dev);
+	}
+
+	return 0;
+};
+
+static void mhi_uci_remove(struct mhi_device *mhi_dev)
+{
+	struct uci_dev *ucidev = dev_get_drvdata(&mhi_dev->dev);
+
+	device_destroy(uci_dev_class, MKDEV(uci_dev_major, ucidev->minor));
+
+	mutex_lock(&ucidev->lock);
+	ucidev->enabled = false;
+	if (ucidev->open_count)
+		__mhi_uci_release(ucidev);
+	mutex_unlock(&ucidev->lock);
+
+	xa_erase(&uci_xa, ucidev->minor);
+	kref_put(&ucidev->ref_count, uci_dev_release);
+}
+
+/* .driver_data stores max mtu */
+static const struct mhi_device_id mhi_uci_match_table[] = {
+	{ .chan = "QAIC_SAHARA", .driver_data = SZ_32K},
+	{},
+};
+MODULE_DEVICE_TABLE(mhi, mhi_uci_match_table);
+
+static struct mhi_driver mhi_uci_driver = {
+	.id_table = mhi_uci_match_table,
+	.remove = mhi_uci_remove,
+	.probe = mhi_uci_probe,
+	.ul_xfer_cb = mhi_uci_ul_xfer_cb,
+	.dl_xfer_cb = mhi_uci_dl_xfer_cb,
+	.driver = {
+		.name = MHI_UCI_DRIVER_NAME,
+	},
+};
+
+int mhi_uci_init(void)
+{
+	int ret;
+
+	ret = register_chrdev(0, MHI_UCI_DRIVER_NAME, &mhidev_fops);
+	if (ret < 0)
+		return ret;
+
+	uci_dev_major = ret;
+	uci_dev_class = class_create(MHI_UCI_DRIVER_NAME);
+	if (IS_ERR(uci_dev_class)) {
+		ret = PTR_ERR(uci_dev_class);
+		goto unregister_chrdev;
+	}
+
+	ret = mhi_driver_register(&mhi_uci_driver);
+	if (ret)
+		goto destroy_class;
+
+	return 0;
+
+destroy_class:
+	class_destroy(uci_dev_class);
+unregister_chrdev:
+	unregister_chrdev(uci_dev_major, MHI_UCI_DRIVER_NAME);
+	return ret;
+}
+
+void mhi_uci_exit(void)
+{
+	mhi_driver_unregister(&mhi_uci_driver);
+	class_destroy(uci_dev_class);
+	unregister_chrdev(uci_dev_major, MHI_UCI_DRIVER_NAME);
+	xa_destroy(&uci_xa);
+}
-- 
2.40.1