[RFC PATCH 21/22] NTB: Add a new NTB client driver to implement VHOST functionality

[Kishon Vijay Abraham I]

Add a new NTB client driver to implement VHOST functionality. When two
hosts are connected using NTB, one of the hosts should run NTB client
driver that implements VIRTIO functionality and the other host should
run NTB client implements VHOST functionality. This interfaces with
VHOST layer so that any vhost client driver can exchange data with
the remote virtio client driver.

Signed-off-by: Kishon Vijay Abraham I <kishon@xxxxxx>
---
 drivers/ntb/Kconfig     |   9 +
 drivers/ntb/Makefile    |   1 +
 drivers/ntb/ntb_vhost.c | 776 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 786 insertions(+)
 create mode 100644 drivers/ntb/ntb_vhost.c

diff --git a/drivers/ntb/Kconfig b/drivers/ntb/Kconfig
index e171b3256f68..7d1b9bb56e71 100644
--- a/drivers/ntb/Kconfig
+++ b/drivers/ntb/Kconfig
@@ -46,4 +46,13 @@ config NTB_VIRTIO
 
 	 If unsure, say N.
 
+config NTB_VHOST
+	tristate "NTB VHOST"
+	help
+	 The NTB vhost driver sits between the NTB HW driver and the vhost
+	 client driver and lets the vhost client driver to exchange data with
+	 the remote virtio driver over the NTB hardware.
+
+	 If unsure, say N.
+
 endif # NTB
diff --git a/drivers/ntb/Makefile b/drivers/ntb/Makefile
index d37ab488bcbc..25c9937c91cf 100644
--- a/drivers/ntb/Makefile
+++ b/drivers/ntb/Makefile
@@ -2,6 +2,7 @@
 obj-$(CONFIG_NTB) += ntb.o hw/ test/
 obj-$(CONFIG_NTB_TRANSPORT) += ntb_transport.o
 obj-$(CONFIG_NTB_VIRTIO) += ntb_virtio.o
+obj-$(CONFIG_NTB_VHOST) += ntb_vhost.o
 
 ntb-y			:= core.o
 ntb-$(CONFIG_NTB_MSI)	+= msi.o
diff --git a/drivers/ntb/ntb_vhost.c b/drivers/ntb/ntb_vhost.c
new file mode 100644
index 000000000000..1d717bb98d85
--- /dev/null
+++ b/drivers/ntb/ntb_vhost.c
@@ -0,0 +1,776 @@
+// SPDX-License-Identifier: GPL-2.0
+/**
+ * NTB Client Driver to implement VHOST functionality
+ *
+ * Copyright (C) 2020 Texas Instruments
+ * Author: Kishon Vijay Abraham I <kishon@xxxxxx>
+ */
+
+#include <linux/module.h>
+#include <linux/ntb.h>
+#include <linux/slab.h>
+#include <linux/vhost.h>
+#include <linux/virtio_pci.h>
+#include <linux/vringh.h>
+
+#include "ntb_virtio.h"
+
+static struct workqueue_struct *kntbvhost_workqueue;
+
+struct ntb_vhost_queue {
+	struct delayed_work db_handler;
+	struct vhost_virtqueue *vq;
+	void __iomem *vq_addr;
+};
+
+struct ntb_vhost {
+	struct ntb_vhost_queue vqueue[MAX_VQS];
+	struct work_struct link_cleanup;
+	struct delayed_work cmd_handler;
+	struct delayed_work link_work;
+	resource_size_t peer_mw_size;
+	struct config_group *group;
+	phys_addr_t peer_mw_addr;
+	struct vhost_dev vdev;
+	struct ntb_dev *ndev;
+	struct vring vring;
+	struct device *dev;
+	u64 virtio_addr;
+	u64 features;
+};
+
+#define to_ntb_vhost(v) container_of((v), struct ntb_vhost, vdev)
+
+/* ntb_vhost_finalize_features - Indicate features are finalized to vhost client
+ *   driver
+ * @ntb: NTB vhost device that communicates with the remote virtio device
+ *
+ * Invoked when the remote virtio device sends HOST_CMD_FINALIZE_FEATURES
+ * command once the feature negotiation is complete. This function sends
+ * notification to the vhost client driver.
+ */
+static void ntb_vhost_finalize_features(struct ntb_vhost *ntb)
+{
+	struct vhost_dev *vdev;
+	struct ntb_dev *ndev;
+	u64 features;
+
+	vdev = &ntb->vdev;
+	ndev = ntb->ndev;
+
+	features = ntb_spad_read(ndev, VIRTIO_FEATURES_UPPER);
+	features <<= 32;
+	features |= ntb_spad_read(ndev, VIRTIO_FEATURES_LOWER);
+	vdev->features = features;
+	blocking_notifier_call_chain(&vdev->notifier, NOTIFY_FINALIZE_FEATURES, 0);
+}
+
+/* ntb_vhost_cmd_handler - Handle commands from remote NTB virtio driver
+ * @work: The work_struct holding the ntb_vhost_cmd_handler() function that is
+ *   scheduled
+ *
+ * Handle commands from the remote NTB virtio driver and sends notification to
+ * the vhost client driver. The remote virtio driver sends commands when the
+ * virtio driver status is updated or when the feature negotiation is complet
+ * or if the virtio driver wants to reset the device.
+ */
+static void ntb_vhost_cmd_handler(struct work_struct *work)
+{
+	struct vhost_dev *vdev;
+	struct ntb_vhost *ntb;
+	struct ntb_dev *ndev;
+	struct device *dev;
+	u8 command;
+
+	ntb = container_of(work, struct ntb_vhost, cmd_handler.work);
+	vdev = &ntb->vdev;
+	ndev = ntb->ndev;
+	dev = ntb->dev;
+
+	command = ntb_spad_read(ndev, VHOST_COMMAND);
+	if (!command)
+		goto reset_handler;
+
+	ntb_spad_write(ndev, VHOST_COMMAND, 0);
+
+	switch (command) {
+	case HOST_CMD_SET_STATUS:
+		blocking_notifier_call_chain(&vdev->notifier, NOTIFY_SET_STATUS, 0);
+		ntb_spad_write(ndev, VHOST_COMMAND_STATUS, HOST_CMD_STATUS_OKAY);
+		break;
+	case HOST_CMD_FINALIZE_FEATURES:
+		ntb_vhost_finalize_features(ntb);
+		ntb_spad_write(ndev, VHOST_COMMAND_STATUS, HOST_CMD_STATUS_OKAY);
+		break;
+	case HOST_CMD_RESET:
+		blocking_notifier_call_chain(&vdev->notifier, NOTIFY_RESET, 0);
+		ntb_spad_write(ndev, VHOST_COMMAND_STATUS, HOST_CMD_STATUS_OKAY);
+		break;
+	default:
+		dev_err(dev, "UNKNOWN command: %d\n", command);
+		break;
+	}
+
+reset_handler:
+	queue_delayed_work(kntbvhost_workqueue, &ntb->cmd_handler,
+			   msecs_to_jiffies(1));
+}
+
+/* ntb_vhost_del_vqs - Delete all the vqs associated with the vhost device
+ * @vdev: Vhost device that communicates with the remote virtio device
+ *
+ * Delete all the vqs associated with the vhost device.
+ */
+void ntb_vhost_del_vqs(struct vhost_dev *vdev)
+{
+	struct ntb_vhost_queue *vqueue;
+	struct vhost_virtqueue *vq;
+	struct ntb_vhost *ntb;
+	int i;
+
+	ntb = to_ntb_vhost(vdev);
+
+	for (i = 0; i < vdev->nvqs; i++) {
+		vq = vdev->vqs[i];
+		if (IS_ERR_OR_NULL(vq))
+			continue;
+
+		vqueue = &ntb->vqueue[i];
+		cancel_delayed_work_sync(&vqueue->db_handler);
+		iounmap(vqueue->vq_addr);
+		kfree(vq);
+	}
+}
+
+/* ntb_vhost_vq_db_work - Handle doorbell event receive for a virtqueue
+ * @work: The work_struct holding the ntb_vhost_vq_db_work() function for every
+ *   created virtqueue
+ *
+ * This function is invoked when the remote virtio driver sends a notification
+ * to the virtqueue. (virtqueue_kick() on the remote virtio driver). This
+ * function invokes the vhost client driver's virtqueue callback.
+ */
+static void ntb_vhost_vq_db_work(struct work_struct *work)
+{
+	struct ntb_vhost_queue *vqueue;
+
+	vqueue = container_of(work, struct ntb_vhost_queue, db_handler.work);
+	vhost_virtqueue_callback(vqueue->vq);
+}
+
+/* ntb_vhost_notify - Send notification to the remote virtqueue
+ * @vq: The local vhost virtqueue corresponding to the remote virtio virtqueue
+ *
+ * Use NTB doorbell to send notification for the remote virtqueue
+ */
+static void ntb_vhost_notify(struct vhost_virtqueue *vq)
+{
+	struct vhost_dev *vdev;
+	struct ntb_vhost *ntb;
+
+	vdev = vq->dev;
+	ntb = to_ntb_vhost(vdev);
+
+	ntb_peer_db_set(ntb->ndev, vq->index);
+}
+
+/* ntb_vhost_create_vq - Create a new vhost virtqueue
+ * @vdev: Vhost device that communicates with the remote virtio device
+ * @index: Index of the vhost virtqueue
+ * @num_bufs: The number of buffers that should be supported by the vhost
+ *   virtqueue (number of descriptors in the vhost virtqueue)
+ * @callback: Callback function associated with the virtqueue
+ *
+ * Create a new vhost virtqueue which can be used by the vhost client driver
+ * to access the remote virtio. This sets up the local address of the vhost
+ * virtqueue but shouldn't be accessed until the virtio sets the status to
+ * VIRTIO_CONFIG_S_DRIVER_OK.
+ */
+static struct vhost_virtqueue *
+ntb_vhost_create_vq(struct vhost_dev *vdev, int index, unsigned int num_bufs,
+		    void (*callback)(struct vhost_virtqueue *))
+{
+	struct ntb_vhost_queue *vqueue;
+	unsigned int vq_size, offset;
+	struct vhost_virtqueue *vq;
+	phys_addr_t vq_phys_addr;
+	phys_addr_t peer_mw_addr;
+	struct vringh *vringh;
+	struct ntb_vhost *ntb;
+	void __iomem *vq_addr;
+	struct ntb_dev *ndev;
+	struct vring *vring;
+	struct device *dev;
+	int ret;
+
+	ntb = to_ntb_vhost(vdev);
+	vqueue = &ntb->vqueue[index];
+	peer_mw_addr = ntb->peer_mw_addr;
+	ndev = ntb->ndev;
+	dev = ntb->dev;
+
+	vq =  kzalloc(sizeof(*vq), GFP_KERNEL);
+	if (!vq)
+		return ERR_PTR(-ENOMEM);
+
+	vq->dev = vdev;
+	vq->callback = callback;
+	vq->num = num_bufs;
+	vq->index = index;
+	vq->notify = ntb_vhost_notify;
+	vq->type = VHOST_TYPE_MMIO;
+
+	vringh = &vq->vringh;
+	vring = &vringh->vring;
+
+	ntb_spad_write(ndev, VHOST_QUEUE_NUM_BUFFERS(index), num_bufs);
+	vq_size = vring_size(num_bufs, VIRTIO_PCI_VRING_ALIGN);
+	offset = index * vq_size;
+	if (offset + vq_size > ntb->peer_mw_size) {
+		dev_err(dev, "Not enough vhost memory for allocating vq\n");
+		ret = -ENOMEM;
+		goto err_out_of_bound;
+	}
+
+	vq_phys_addr = peer_mw_addr + offset;
+	vq_addr = ioremap_wc(vq_phys_addr, vq_size);
+	if (!vq_addr) {
+		dev_err(dev, "Fail to ioremap virtqueue address\n");
+		ret = -ENOMEM;
+		goto err_out_of_bound;
+	}
+
+	vqueue->vq = vq;
+	vqueue->vq_addr = vq_addr;
+
+	vring_init(vring, num_bufs, vq_addr, VIRTIO_PCI_VRING_ALIGN);
+	ret = vringh_init_mmio(vringh, ntb->features, num_bufs, false,
+			       vring->desc, vring->avail, vring->used);
+	if (ret) {
+		dev_err(dev, "Failed to init vringh\n");
+		goto err_init_mmio;
+	}
+
+	INIT_DELAYED_WORK(&vqueue->db_handler, ntb_vhost_vq_db_work);
+
+	return vq;
+
+err_init_mmio:
+	iounmap(vq_addr);
+
+err_out_of_bound:
+	kfree(vq);
+
+	return ERR_PTR(ret);
+}
+
+/* ntb_vhost_create_vqs - Create vhost virtqueues for vhost device
+ * @vdev: Vhost device that communicates with the remote virtio device
+ * @nvqs: Number of vhost virtqueues to be created
+ * @num_bufs: The number of buffers that should be supported by the vhost
+ *   virtqueue (number of descriptors in the vhost virtqueue)
+ * @vqs: Pointers to all the created vhost virtqueues
+ * @callback: Callback function associated with the virtqueue
+ * @names: Names associated with each virtqueue
+ *
+ * Create vhost virtqueues for vhost device. This acts as a wrapper to
+ * ntb_vhost_create_vq() which creates individual vhost virtqueue.
+ */
+static int ntb_vhost_create_vqs(struct vhost_dev *vdev, unsigned int nvqs,
+				unsigned int num_bufs,
+				struct vhost_virtqueue *vqs[],
+				vhost_vq_callback_t *callbacks[],
+				const char * const names[])
+{
+	struct ntb_vhost *ntb;
+	struct device *dev;
+	int ret, i;
+
+	ntb = to_ntb_vhost(vdev);
+	dev = ntb->dev;
+
+	for (i = 0; i < nvqs; i++) {
+		vqs[i] = ntb_vhost_create_vq(vdev, i, num_bufs, callbacks[i]);
+		if (IS_ERR_OR_NULL(vqs[i])) {
+			ret = PTR_ERR(vqs[i]);
+			dev_err(dev, "Failed to create virtqueue\n");
+			goto err;
+		}
+	}
+
+	vdev->nvqs = nvqs;
+	vdev->vqs = vqs;
+
+	return 0;
+
+err:
+	ntb_vhost_del_vqs(vdev);
+
+	return ret;
+}
+
+/* ntb_vhost_write - Write data to buffer provided by remote virtio driver
+ * @vdev: Vhost device that communicates with the remote virtio device
+ * @dst: Buffer address in the remote device provided by the remote virtio
+ *   driver
+ * @src: Buffer address in the local device provided by the vhost client driver
+ * @len: Length of the data to be copied from @src to @dst
+ *
+ * Write data to buffer provided by remote virtio driver from buffer provided
+ * by vhost client driver.
+ */
+static int ntb_vhost_write(struct vhost_dev *vdev, u64 dst, void *src, int len)
+{
+	phys_addr_t peer_mw_addr, phys_addr;
+	struct ntb_vhost *ntb;
+	unsigned int offset;
+	struct device *dev;
+	u64 virtio_addr;
+	void *addr;
+
+	ntb = to_ntb_vhost(vdev);
+	dev = ntb->dev;
+
+	peer_mw_addr = ntb->peer_mw_addr;
+	virtio_addr = ntb->virtio_addr;
+
+	offset = dst -  virtio_addr;
+	if (offset + len > ntb->peer_mw_size) {
+		dev_err(dev, "Overflow of vhost memory\n");
+		return -EINVAL;
+	}
+
+	phys_addr = peer_mw_addr + offset;
+	addr = ioremap_wc(phys_addr, len);
+	if (!addr) {
+		dev_err(dev, "Failed to ioremap vhost address\n");
+		return -ENOMEM;
+	}
+
+	memcpy_toio(addr, src, len);
+	iounmap(addr);
+
+	return 0;
+}
+
+/* ntb_vhost_read - Read data from buffers provided by remote virtio driver
+ * @vdev: Vhost device that communicates with the remote virtio device
+ * @dst: Buffer address in the local device provided by the vhost client driver
+ * @src: Buffer address in the remote device provided by the remote virtio
+ *   driver
+ * @len: Length of the data to be copied from @src to @dst
+ *
+ * Read data from buffers provided by remote virtio driver to address provided
+ * by vhost client driver.
+ */
+static int ntb_vhost_read(struct vhost_dev *vdev, void *dst, u64 src, int len)
+{
+	phys_addr_t peer_mw_addr, phys_addr;
+	struct ntb_vhost *ntb;
+	unsigned int offset;
+	struct device *dev;
+	u64 virtio_addr;
+	void *addr;
+
+	ntb = to_ntb_vhost(vdev);
+	dev = ntb->dev;
+
+	peer_mw_addr = ntb->peer_mw_addr;
+	virtio_addr = ntb->virtio_addr;
+
+	offset = src - virtio_addr;
+	if (offset + len > ntb->peer_mw_size) {
+		dev_err(dev, "Overflow of vhost memory\n");
+		return -EINVAL;
+	}
+
+	phys_addr = peer_mw_addr + offset;
+	addr = ioremap_wc(phys_addr, len);
+	if (!addr) {
+		dev_err(dev, "Failed to ioremap vhost address\n");
+		return -ENOMEM;
+	}
+
+	memcpy_fromio(dst, addr, len);
+	iounmap(addr);
+
+	return 0;
+}
+
+/* ntb_vhost_release - Callback function to free device
+ * @dev: Device in vhost_dev that has to be freed
+ *
+ * Callback function from device core invoked to free the device after
+ * all references have been removed. This frees the allocated memory for
+ * struct ntb_vhost.
+ */
+static void ntb_vhost_release(struct device *dev)
+{
+	struct vhost_dev *vdev;
+	struct ntb_vhost *ntb;
+
+	vdev = to_vhost_dev(dev);
+	ntb = to_ntb_vhost(vdev);
+
+	kfree(ntb);
+}
+
+/* ntb_vhost_set_features - vhost_config_ops to set vhost device features
+ * @vdev: Vhost device that communicates with the remote virtio device
+ * @features: Features supported by the vhost client driver
+ *
+ * vhost_config_ops invoked by the vhost client driver to set vhost device
+ * features.
+ */
+static int ntb_vhost_set_features(struct vhost_dev *vdev, u64 features)
+{
+	struct ntb_vhost *ntb;
+	struct ntb_dev *ndev;
+
+	ntb = to_ntb_vhost(vdev);
+	ndev = ntb->ndev;
+
+	ntb_spad_write(ndev, VHOST_FEATURES_LOWER, lower_32_bits(features));
+	ntb_spad_write(ndev, VHOST_FEATURES_UPPER, upper_32_bits(features));
+	ntb->features = features;
+
+	return 0;
+}
+
+/* ntb_vhost_set_status - vhost_config_ops to set vhost device status
+ * @vdev: Vhost device that communicates with the remote virtio device
+ * @status: Vhost device status configured by vhost client driver
+ *
+ * vhost_config_ops invoked by the vhost client driver to set vhost device
+ * status.
+ */
+static int ntb_vhost_set_status(struct vhost_dev *vdev, u8 status)
+{
+	struct ntb_vhost *ntb;
+	struct ntb_dev *ndev;
+
+	ntb = to_ntb_vhost(vdev);
+	ndev = ntb->ndev;
+
+	ntb_spad_write(ndev, VHOST_DEVICE_STATUS, status);
+
+	return 0;
+}
+
+/* ntb_vhost_get_status - vhost_config_ops to get vhost device status
+ * @vdev: Vhost device that communicates with the remote virtio device
+ *
+ * vhost_config_ops invoked by the vhost client driver to get vhost device
+ * status set by the remote virtio driver.
+ */
+static u8 ntb_vhost_get_status(struct vhost_dev *vdev)
+{
+	struct ntb_vhost *ntb;
+	struct ntb_dev *ndev;
+
+	ntb = to_ntb_vhost(vdev);
+	ndev = ntb->ndev;
+
+	return ntb_spad_read(ndev, VHOST_DEVICE_STATUS);
+}
+
+static const struct vhost_config_ops ops = {
+	.create_vqs	= ntb_vhost_create_vqs,
+	.del_vqs	= ntb_vhost_del_vqs,
+	.write		= ntb_vhost_write,
+	.read		= ntb_vhost_read,
+	.set_features	= ntb_vhost_set_features,
+	.set_status	= ntb_vhost_set_status,
+	.get_status	= ntb_vhost_get_status,
+};
+
+/* ntb_vhost_link_cleanup - Cleanup once link to the remote host is lost
+ * @ntb: NTB vhost device that communicates with the remote virtio device
+ *
+ * Performs the cleanup that has to be done once the link to the remote host
+ * is lost or when the NTB vhost driver is removed.
+ */
+static void ntb_vhost_link_cleanup(struct ntb_vhost *ntb)
+{
+	cancel_delayed_work_sync(&ntb->link_work);
+}
+
+/* ntb_vhost_link_cleanup_work - Cleanup once link to the remote host is lost
+ * @work: The work_struct holding the ntb_vhost_link_cleanup_work() function
+ *   that is scheduled
+ *
+ * Performs the cleanup that has to be done once the link to the remote host
+ * is lost. This acts as a wrapper to ntb_vhost_link_cleanup() for the cleanup
+ * operation.
+ */
+static void ntb_vhost_link_cleanup_work(struct work_struct *work)
+{
+	struct ntb_vhost *ntb;
+
+	ntb = container_of(work, struct ntb_vhost, link_cleanup);
+	ntb_vhost_link_cleanup(ntb);
+}
+
+/* ntb_vhost_link_work - Initialization once link to the remote host is
+ *   established
+ * @work: The work_struct holding the ntb_vhost_link_work() function that is
+ *   scheduled
+ *
+ * Performs the NTB vhost initialization that has to be done once the link to
+ * the remote host is established. Initializes the scratchpad registers with
+ * data required for the remote NTB virtio driver to establish communication
+ * with this vhost driver.
+ */
+static void ntb_vhost_link_work(struct work_struct *work)
+{
+	struct vhost_dev *vdev;
+	struct ntb_vhost *ntb;
+	struct ntb_dev *ndev;
+	struct device *dev;
+	u64 virtio_addr;
+	u32 type;
+
+	ntb = container_of(work, struct ntb_vhost, link_work.work);
+	vdev = &ntb->vdev;
+	ndev = ntb->ndev;
+	dev = ntb->dev;
+
+	/*
+	 * Device will be registered when vhost client driver is linked to
+	 * vhost transport device driver in configfs.
+	 */
+	if (!device_is_registered(&vdev->dev))
+		goto out;
+
+	/*
+	 * This is unlikely to happen if "vhost" configfs is used for
+	 * registering vhost device.
+	 */
+	if (vdev->id.device == 0 && vdev->id.vendor == 0) {
+		dev_err(dev, "vhost device is registered without valid ID\n");
+		goto out;
+	}
+
+	ntb_spad_write(ndev, VHOST_VENDORID, vdev->id.vendor);
+	ntb_spad_write(ndev, VHOST_DEVICEID, vdev->id.device);
+	ntb_peer_spad_write(ndev, NTB_DEF_PEER_IDX, VIRTIO_TYPE, TYPE_VHOST);
+
+	type = ntb_spad_read(ndev, VIRTIO_TYPE);
+	if (type != TYPE_VIRTIO)
+		goto out;
+
+	virtio_addr = ntb_spad_read(ndev,  VIRTIO_MW0_UPPER_ADDR);
+	virtio_addr <<= 32;
+	virtio_addr |= ntb_spad_read(ndev, VIRTIO_MW0_LOWER_ADDR);
+	ntb->virtio_addr = virtio_addr;
+
+	INIT_DELAYED_WORK(&ntb->cmd_handler, ntb_vhost_cmd_handler);
+	queue_work(kntbvhost_workqueue, &ntb->cmd_handler.work);
+
+	return;
+
+out:
+	if (ntb_link_is_up(ndev, NULL, NULL) == 1)
+		schedule_delayed_work(&ntb->link_work,
+				      msecs_to_jiffies(NTB_LINK_DOWN_TIMEOUT));
+}
+
+/* ntb_vhost_event_callback - Callback to link event interrupt
+ * @data: Private data specific to NTB vhost driver
+ *
+ * Callback function from NTB HW driver whenever both the hosts in the NTB
+ * setup has invoked ntb_link_enable().
+ */
+static void ntb_vhost_event_callback(void *data)
+{
+	struct ntb_vhost *ntb;
+	struct ntb_dev *ndev;
+
+	ntb = data;
+	ndev = ntb->ndev;
+
+	if (ntb_link_is_up(ntb->ndev, NULL, NULL) == 1)
+		schedule_delayed_work(&ntb->link_work, 0);
+	else
+		schedule_work(&ntb->link_cleanup);
+}
+
+/* ntb_vhost_vq_db_callback - Callback to doorbell interrupt to handle vhost
+ *   virtqueue work
+ * @data: Private data specific to NTB vhost driver
+ * @vector: Doorbell vector on which interrupt is received
+ *
+ * Callback function from NTB HW driver whenever remote virtio driver has sent
+ * a notification using doorbell. This schedules work corresponding to the
+ * virtqueue for which notification has been received.
+ */
+static void ntb_vhost_vq_db_callback(void *data, int vector)
+{
+	struct ntb_vhost_queue *vqueue;
+	struct ntb_vhost *ntb;
+
+	ntb = data;
+	vqueue = &ntb->vqueue[vector - 1];
+
+	schedule_delayed_work(&vqueue->db_handler, 0);
+}
+
+static const struct ntb_ctx_ops ntb_vhost_ops = {
+	.link_event = ntb_vhost_event_callback,
+	.db_event = ntb_vhost_vq_db_callback,
+};
+
+/* ntb_vhost_configure_mw - Get memory window address and size
+ * @ntb: NTB vhost device that communicates with the remote virtio device
+ *
+ * Get address and size of memory window 0 and update the size of
+ * memory window 0 to scratchpad register in order for virtio driver
+ * to get the memory window size.
+ *
+ * TODO: Add support for multiple memory windows.
+ */
+static int ntb_vhost_configure_mw(struct ntb_vhost *ntb)
+{
+	struct ntb_dev *ndev;
+	struct device *dev;
+	int ret;
+
+	ndev = ntb->ndev;
+	dev = ntb->dev;
+
+	ret = ntb_peer_mw_get_addr(ndev, 0, &ntb->peer_mw_addr, &ntb->peer_mw_size);
+	if (ret) {
+		dev_err(dev, "Failed to get memory window address\n");
+		return ret;
+	}
+
+	ntb_spad_write(ndev, VHOST_MW0_SIZE_LOWER, lower_32_bits(ntb->peer_mw_size));
+	ntb_spad_write(ndev, VHOST_MW0_SIZE_UPPER, upper_32_bits(ntb->peer_mw_size));
+
+	return 0;
+}
+
+/* ntb_vhost_probe - Initialize struct ntb_vhost when a new NTB device is
+ *   created
+ * @client: struct ntb_client * representing the ntb vhost client driver
+ * @ndev: NTB device created by NTB HW driver
+ *
+ * Probe function to initialize struct ntb_vhost when a new NTB device is
+ * created. Also get the supported MW0 size and MW0 address and write the MW0
+ * address to the self scratchpad for the remote NTB virtio driver to read.
+ */
+static int ntb_vhost_probe(struct ntb_client *self, struct ntb_dev *ndev)
+{
+	struct device *dev = &ndev->dev;
+	struct config_group *group;
+	struct vhost_dev *vdev;
+	struct ntb_vhost *ntb;
+	int ret;
+
+	ntb = kzalloc(sizeof(*ntb), GFP_KERNEL);
+	if (!ntb)
+		return -ENOMEM;
+
+	ntb->ndev = ndev;
+	ntb->dev = dev;
+
+	ret = ntb_vhost_configure_mw(ntb);
+	if (ret) {
+		dev_err(dev, "Failed to configure memory window\n");
+		goto err;
+	}
+
+	ret = ntb_set_ctx(ndev, ntb, &ntb_vhost_ops);
+	if (ret) {
+		dev_err(dev, "Failed to set NTB vhost context\n");
+		goto err;
+	}
+
+	vdev = &ntb->vdev;
+	vdev->dev.parent = dev;
+	vdev->dev.release = ntb_vhost_release;
+	vdev->ops = &ops;
+
+	group = vhost_cfs_add_device_item(vdev);
+	if (IS_ERR(group)) {
+		dev_err(dev, "Failed to add configfs entry for vhost device\n");
+		goto err;
+	}
+
+	ntb->group = group;
+
+	INIT_DELAYED_WORK(&ntb->link_work, ntb_vhost_link_work);
+	INIT_WORK(&ntb->link_cleanup, ntb_vhost_link_cleanup_work);
+
+	ntb_link_enable(ndev, NTB_SPEED_AUTO, NTB_WIDTH_AUTO);
+
+	return 0;
+
+err:
+	kfree(ntb);
+
+	return ret;
+}
+
+/* ntb_vhost_free - Free the initializations performed by ntb_vhost_probe()
+ * @client: struct ntb_client * representing the ntb vhost client driver
+ * @ndev: NTB device created by NTB HW driver
+ *
+ * Free the initializations performed by ntb_vhost_probe().
+ */
+void ntb_vhost_free(struct ntb_client *client, struct ntb_dev *ndev)
+{
+	struct config_group *group;
+	struct vhost_dev *vdev;
+	struct ntb_vhost *ntb;
+
+	ntb = ndev->ctx;
+	vdev = &ntb->vdev;
+	group = ntb->group;
+
+	ntb_vhost_link_cleanup(ntb);
+	ntb_link_disable(ndev);
+	ntb_vhost_del_vqs(vdev);
+	vhost_cfs_remove_device_item(group);
+	if (device_is_registered(&vdev->dev))
+		vhost_unregister_device(vdev);
+}
+
+static struct ntb_client ntb_vhost_client = {
+	.ops = {
+		.probe = ntb_vhost_probe,
+		.remove = ntb_vhost_free,
+	},
+};
+
+static int __init ntb_vhost_init(void)
+{
+	int ret;
+
+	kntbvhost_workqueue = alloc_workqueue("kntbvhost", WQ_MEM_RECLAIM |
+					      WQ_HIGHPRI, 0);
+	if (!kntbvhost_workqueue) {
+		pr_err("Failed to allocate kntbvhost_workqueue\n");
+		return -ENOMEM;
+	}
+
+	ret = ntb_register_client(&ntb_vhost_client);
+	if (ret) {
+		pr_err("Failed to register ntb vhost driver --> %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+module_init(ntb_vhost_init);
+
+static void __exit ntb_vhost_exit(void)
+{
+	ntb_unregister_client(&ntb_vhost_client);
+	destroy_workqueue(kntbvhost_workqueue);
+}
+module_exit(ntb_vhost_exit);
+
+MODULE_DESCRIPTION("NTB VHOST Driver");
+MODULE_AUTHOR("Kishon Vijay Abraham I <kishon@xxxxxx>");
+MODULE_LICENSE("GPL v2");
-- 
2.17.1