drivers/gpu/drm/virtio/virtgpu_vq.c

/*
 * Copyright (C) 2015 Red Hat, Inc.
 * All Rights Reserved.
 *
 * Authors:
 *    Dave Airlie <airlied@redhat.com>
 *    Gerd Hoffmann <kraxel@redhat.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * VA LINUX SYSTEMS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

#include <drm/drmP.h>
#include "virtgpu_drv.h"
#include <linux/virtio.h>
#include <linux/virtio_config.h>
#include <linux/virtio_ring.h>

#define MAX_INLINE_CMD_SIZE   96
#define MAX_INLINE_RESP_SIZE  24
#define VBUFFER_SIZE          (sizeof(struct virtio_gpu_vbuffer) \
			       + MAX_INLINE_CMD_SIZE		 \
			       + MAX_INLINE_RESP_SIZE)

void virtio_gpu_resource_id_get(struct virtio_gpu_device *vgdev,
				uint32_t *resid)
{
	int handle;

	idr_preload(GFP_KERNEL);
	spin_lock(&vgdev->resource_idr_lock);
	handle = idr_alloc(&vgdev->resource_idr, NULL, 1, 0, GFP_NOWAIT);
	spin_unlock(&vgdev->resource_idr_lock);
	idr_preload_end();
	*resid = handle;
}

void virtio_gpu_resource_id_put(struct virtio_gpu_device *vgdev, uint32_t id)
{
	spin_lock(&vgdev->resource_idr_lock);
	idr_remove(&vgdev->resource_idr, id);
	spin_unlock(&vgdev->resource_idr_lock);
}

void virtio_gpu_ctrl_ack(struct virtqueue *vq)
{
	struct drm_device *dev = vq->vdev->priv;
	struct virtio_gpu_device *vgdev = dev->dev_private;
	schedule_work(&vgdev->ctrlq.dequeue_work);
}

void virtio_gpu_cursor_ack(struct virtqueue *vq)
{
	struct drm_device *dev = vq->vdev->priv;
	struct virtio_gpu_device *vgdev = dev->dev_private;
	schedule_work(&vgdev->cursorq.dequeue_work);
}

int virtio_gpu_alloc_vbufs(struct virtio_gpu_device *vgdev)
{
	struct virtio_gpu_vbuffer *vbuf;
	int i, size, count = 0;
	void *ptr;

	INIT_LIST_HEAD(&vgdev->free_vbufs);
	spin_lock_init(&vgdev->free_vbufs_lock);
	count += virtqueue_get_vring_size(vgdev->ctrlq.vq);
	count += virtqueue_get_vring_size(vgdev->cursorq.vq);
	size = count * VBUFFER_SIZE;
	DRM_INFO("virtio vbuffers: %d bufs, %zdB each, %dkB total.\n",
		 count, VBUFFER_SIZE, size / 1024);

	vgdev->vbufs = kzalloc(size, GFP_KERNEL);
	if (!vgdev->vbufs)
		return -ENOMEM;

	for (i = 0, ptr = vgdev->vbufs;
	     i < count;
	     i++, ptr += VBUFFER_SIZE) {
		vbuf = ptr;
		list_add(&vbuf->list, &vgdev->free_vbufs);
	}
	return 0;
}

void virtio_gpu_free_vbufs(struct virtio_gpu_device *vgdev)
{
	struct virtio_gpu_vbuffer *vbuf;
	int i, count = 0;

	count += virtqueue_get_vring_size(vgdev->ctrlq.vq);
	count += virtqueue_get_vring_size(vgdev->cursorq.vq);

	spin_lock(&vgdev->free_vbufs_lock);
	for (i = 0; i < count; i++) {
		if (WARN_ON(list_empty(&vgdev->free_vbufs)))
			return;
		vbuf = list_first_entry(&vgdev->free_vbufs,
					struct virtio_gpu_vbuffer, list);
		list_del(&vbuf->list);
	}
	spin_unlock(&vgdev->free_vbufs_lock);
	kfree(vgdev->vbufs);
}

static struct virtio_gpu_vbuffer*
virtio_gpu_get_vbuf(struct virtio_gpu_device *vgdev,
		    int size, int resp_size, void *resp_buf,
		    virtio_gpu_resp_cb resp_cb)
{
	struct virtio_gpu_vbuffer *vbuf;

	spin_lock(&vgdev->free_vbufs_lock);
	BUG_ON(list_empty(&vgdev->free_vbufs));
	vbuf = list_first_entry(&vgdev->free_vbufs,
				struct virtio_gpu_vbuffer, list);
	list_del(&vbuf->list);
	spin_unlock(&vgdev->free_vbufs_lock);
	memset(vbuf, 0, VBUFFER_SIZE);

	BUG_ON(size > MAX_INLINE_CMD_SIZE);
	vbuf->buf = (void *)vbuf + sizeof(*vbuf);
	vbuf->size = size;

	vbuf->resp_cb = resp_cb;
	vbuf->resp_size = resp_size;
	if (resp_size <= MAX_INLINE_RESP_SIZE)
		vbuf->resp_buf = (void *)vbuf->buf + size;
	else
		vbuf->resp_buf = resp_buf;
	BUG_ON(!vbuf->resp_buf);
	return vbuf;
}

static void *virtio_gpu_alloc_cmd(struct virtio_gpu_device *vgdev,
				  struct virtio_gpu_vbuffer **vbuffer_p,
				  int size)
{
	struct virtio_gpu_vbuffer *vbuf;

	vbuf = virtio_gpu_get_vbuf(vgdev, size,
				   sizeof(struct virtio_gpu_ctrl_hdr),
				   NULL, NULL);
	if (IS_ERR(vbuf)) {
		*vbuffer_p = NULL;
		return ERR_CAST(vbuf);
	}
	*vbuffer_p = vbuf;
	return vbuf->buf;
}

static struct virtio_gpu_update_cursor*
virtio_gpu_alloc_cursor(struct virtio_gpu_device *vgdev,
			struct virtio_gpu_vbuffer **vbuffer_p)
{
	struct virtio_gpu_vbuffer *vbuf;

	vbuf = virtio_gpu_get_vbuf
		(vgdev, sizeof(struct virtio_gpu_update_cursor),
		 0, NULL, NULL);
	if (IS_ERR(vbuf)) {
		*vbuffer_p = NULL;
		return ERR_CAST(vbuf);
	}
	*vbuffer_p = vbuf;
	return (struct virtio_gpu_update_cursor *)vbuf->buf;
}

static void *virtio_gpu_alloc_cmd_resp(struct virtio_gpu_device *vgdev,
				       virtio_gpu_resp_cb cb,
				       struct virtio_gpu_vbuffer **vbuffer_p,
				       int cmd_size, int resp_size,
				       void *resp_buf)
{
	struct virtio_gpu_vbuffer *vbuf;

	vbuf = virtio_gpu_get_vbuf(vgdev, cmd_size,
				   resp_size, resp_buf, cb);
	if (IS_ERR(vbuf)) {
		*vbuffer_p = NULL;
		return ERR_CAST(vbuf);
	}
	*vbuffer_p = vbuf;
	return (struct virtio_gpu_command *)vbuf->buf;
}

static void free_vbuf(struct virtio_gpu_device *vgdev,
		      struct virtio_gpu_vbuffer *vbuf)
{
	if (vbuf->resp_size > MAX_INLINE_RESP_SIZE)
		kfree(vbuf->resp_buf);
	kfree(vbuf->data_buf);
	spin_lock(&vgdev->free_vbufs_lock);
	list_add(&vbuf->list, &vgdev->free_vbufs);
	spin_unlock(&vgdev->free_vbufs_lock);
}

static void reclaim_vbufs(struct virtqueue *vq, struct list_head *reclaim_list)
{
	struct virtio_gpu_vbuffer *vbuf;
	unsigned int len;
	int freed = 0;

	while ((vbuf = virtqueue_get_buf(vq, &len))) {
		list_add_tail(&vbuf->list, reclaim_list);
		freed++;
	}
	if (freed == 0)
		DRM_DEBUG("Huh? zero vbufs reclaimed");
}

void virtio_gpu_dequeue_ctrl_func(struct work_struct *work)
{
	struct virtio_gpu_device *vgdev =
		container_of(work, struct virtio_gpu_device,
			     ctrlq.dequeue_work);
	struct list_head reclaim_list;
	struct virtio_gpu_vbuffer *entry, *tmp;
	struct virtio_gpu_ctrl_hdr *resp;
	u64 fence_id = 0;

	INIT_LIST_HEAD(&reclaim_list);
	spin_lock(&vgdev->ctrlq.qlock);
	do {
		virtqueue_disable_cb(vgdev->ctrlq.vq);
		reclaim_vbufs(vgdev->ctrlq.vq, &reclaim_list);

	} while (!virtqueue_enable_cb(vgdev->ctrlq.vq));
	spin_unlock(&vgdev->ctrlq.qlock);

	list_for_each_entry_safe(entry, tmp, &reclaim_list, list) {
		resp = (struct virtio_gpu_ctrl_hdr *)entry->resp_buf;
		if (resp->type != cpu_to_le32(VIRTIO_GPU_RESP_OK_NODATA))
			DRM_DEBUG("response 0x%x\n", le32_to_cpu(resp->type));
		if (resp->flags & cpu_to_le32(VIRTIO_GPU_FLAG_FENCE)) {
			u64 f = le64_to_cpu(resp->fence_id);

			if (fence_id > f) {
				DRM_ERROR("%s: Oops: fence %llx -> %llx\n",
					  __func__, fence_id, f);
			} else {
				fence_id = f;
			}
		}
		if (entry->resp_cb)
			entry->resp_cb(vgdev, entry);

		list_del(&entry->list);
		free_vbuf(vgdev, entry);
	}
	wake_up(&vgdev->ctrlq.ack_queue);

	if (fence_id)
		virtio_gpu_fence_event_process(vgdev, fence_id);
}

void virtio_gpu_dequeue_cursor_func(struct work_struct *work)
{
	struct virtio_gpu_device *vgdev =
		container_of(work, struct virtio_gpu_device,
			     cursorq.dequeue_work);
	struct list_head reclaim_list;
	struct virtio_gpu_vbuffer *entry, *tmp;

	INIT_LIST_HEAD(&reclaim_list);
	spin_lock(&vgdev->cursorq.qlock);
	do {
		virtqueue_disable_cb(vgdev->cursorq.vq);
		reclaim_vbufs(vgdev->cursorq.vq, &reclaim_list);
	} while (!virtqueue_enable_cb(vgdev->cursorq.vq));
	spin_unlock(&vgdev->cursorq.qlock);

	list_for_each_entry_safe(entry, tmp, &reclaim_list, list) {
		list_del(&entry->list);
		free_vbuf(vgdev, entry);
	}
	wake_up(&vgdev->cursorq.ack_queue);
}

static int virtio_gpu_queue_ctrl_buffer(struct virtio_gpu_device *vgdev,
					struct virtio_gpu_vbuffer *vbuf)
{
	struct virtqueue *vq = vgdev->ctrlq.vq;
	struct scatterlist *sgs[3], vcmd, vout, vresp;
	int outcnt = 0, incnt = 0;
	int ret;

	if (!vgdev->vqs_ready)
		return -ENODEV;

	sg_init_one(&vcmd, vbuf->buf, vbuf->size);
	sgs[outcnt+incnt] = &vcmd;
	outcnt++;

	if (vbuf->data_size) {
		sg_init_one(&vout, vbuf->data_buf, vbuf->data_size);
		sgs[outcnt + incnt] = &vout;
		outcnt++;
	}

	if (vbuf->resp_size) {
		sg_init_one(&vresp, vbuf->resp_buf, vbuf->resp_size);
		sgs[outcnt + incnt] = &vresp;
		incnt++;
	}

	spin_lock(&vgdev->ctrlq.qlock);
retry:
	ret = virtqueue_add_sgs(vq, sgs, outcnt, incnt, vbuf, GFP_ATOMIC);
	if (ret == -ENOSPC) {
		spin_unlock(&vgdev->ctrlq.qlock);
		wait_event(vgdev->ctrlq.ack_queue, vq->num_free);
		spin_lock(&vgdev->ctrlq.qlock);
		goto retry;
	} else {
		virtqueue_kick(vq);
	}
	spin_unlock(&vgdev->ctrlq.qlock);

	if (!ret)
		ret = vq->num_free;
	return ret;
}

static int virtio_gpu_queue_cursor(struct virtio_gpu_device *vgdev,
				   struct virtio_gpu_vbuffer *vbuf)
{
	struct virtqueue *vq = vgdev->cursorq.vq;
	struct scatterlist *sgs[1], ccmd;
	int ret;
	int outcnt;

	if (!vgdev->vqs_ready)
		return -ENODEV;

	sg_init_one(&ccmd, vbuf->buf, vbuf->size);
	sgs[0] = &ccmd;
	outcnt = 1;

	spin_lock(&vgdev->cursorq.qlock);
retry:
	ret = virtqueue_add_sgs(vq, sgs, outcnt, 0, vbuf, GFP_ATOMIC);
	if (ret == -ENOSPC) {
		spin_unlock(&vgdev->cursorq.qlock);
		wait_event(vgdev->cursorq.ack_queue, vq->num_free);
		spin_lock(&vgdev->cursorq.qlock);
		goto retry;
	} else {
		virtqueue_kick(vq);
	}

	spin_unlock(&vgdev->cursorq.qlock);

	if (!ret)
		ret = vq->num_free;
	return ret;
}

/* just create gem objects for userspace and long lived objects,
   just use dma_alloced pages for the queue objects? */

/* create a basic resource */
void virtio_gpu_cmd_create_resource(struct virtio_gpu_device *vgdev,
				    uint32_t resource_id,
				    uint32_t format,
				    uint32_t width,
				    uint32_t height)
{
	struct virtio_gpu_resource_create_2d *cmd_p;
	struct virtio_gpu_vbuffer *vbuf;

	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
	memset(cmd_p, 0, sizeof(*cmd_p));

	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_RESOURCE_CREATE_2D);
	cmd_p->resource_id = cpu_to_le32(resource_id);
	cmd_p->format = cpu_to_le32(format);
	cmd_p->width = cpu_to_le32(width);
	cmd_p->height = cpu_to_le32(height);

	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
}

void virtio_gpu_cmd_unref_resource(struct virtio_gpu_device *vgdev,
				   uint32_t resource_id)
{
	struct virtio_gpu_resource_unref *cmd_p;
	struct virtio_gpu_vbuffer *vbuf;

	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
	memset(cmd_p, 0, sizeof(*cmd_p));

	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_RESOURCE_UNREF);
	cmd_p->resource_id = cpu_to_le32(resource_id);

	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
}

void virtio_gpu_cmd_resource_inval_backing(struct virtio_gpu_device *vgdev,
					   uint32_t resource_id)
{
	struct virtio_gpu_resource_detach_backing *cmd_p;
	struct virtio_gpu_vbuffer *vbuf;

	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
	memset(cmd_p, 0, sizeof(*cmd_p));

	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING);
	cmd_p->resource_id = cpu_to_le32(resource_id);

	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
}

void virtio_gpu_cmd_set_scanout(struct virtio_gpu_device *vgdev,
				uint32_t scanout_id, uint32_t resource_id,
				uint32_t width, uint32_t height,
				uint32_t x, uint32_t y)
{
	struct virtio_gpu_set_scanout *cmd_p;
	struct virtio_gpu_vbuffer *vbuf;

	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
	memset(cmd_p, 0, sizeof(*cmd_p));

	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_SET_SCANOUT);
	cmd_p->resource_id = cpu_to_le32(resource_id);
	cmd_p->scanout_id = cpu_to_le32(scanout_id);
	cmd_p->r.width = cpu_to_le32(width);
	cmd_p->r.height = cpu_to_le32(height);
	cmd_p->r.x = cpu_to_le32(x);
	cmd_p->r.y = cpu_to_le32(y);

	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
}

void virtio_gpu_cmd_resource_flush(struct virtio_gpu_device *vgdev,
				   uint32_t resource_id,
				   uint32_t x, uint32_t y,
				   uint32_t width, uint32_t height)
{
	struct virtio_gpu_resource_flush *cmd_p;
	struct virtio_gpu_vbuffer *vbuf;

	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
	memset(cmd_p, 0, sizeof(*cmd_p));

	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_RESOURCE_FLUSH);
	cmd_p->resource_id = cpu_to_le32(resource_id);
	cmd_p->r.width = cpu_to_le32(width);
	cmd_p->r.height = cpu_to_le32(height);
	cmd_p->r.x = cpu_to_le32(x);
	cmd_p->r.y = cpu_to_le32(y);

	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
}

void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
					uint32_t resource_id, uint64_t offset,
					__le32 width, __le32 height,
					__le32 x, __le32 y,
					struct virtio_gpu_fence **fence)
{
	struct virtio_gpu_transfer_to_host_2d *cmd_p;
	struct virtio_gpu_vbuffer *vbuf;

	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
	memset(cmd_p, 0, sizeof(*cmd_p));

	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_TRANSFER_TO_HOST_2D);
	cmd_p->resource_id = cpu_to_le32(resource_id);
	cmd_p->offset = cpu_to_le64(offset);
	cmd_p->r.width = width;
	cmd_p->r.height = height;
	cmd_p->r.x = x;
	cmd_p->r.y = y;

	if (fence)
		virtio_gpu_fence_emit(vgdev, &cmd_p->hdr, fence);
	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
}

static void
virtio_gpu_cmd_resource_attach_backing(struct virtio_gpu_device *vgdev,
				       uint32_t resource_id,
				       struct virtio_gpu_mem_entry *ents,
				       uint32_t nents,
				       struct virtio_gpu_fence **fence)
{
	struct virtio_gpu_resource_attach_backing *cmd_p;
	struct virtio_gpu_vbuffer *vbuf;

	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
	memset(cmd_p, 0, sizeof(*cmd_p));

	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_RESOURCE_ATTACH_BACKING);
	cmd_p->resource_id = cpu_to_le32(resource_id);
	cmd_p->nr_entries = cpu_to_le32(nents);

	vbuf->data_buf = ents;
	vbuf->data_size = sizeof(*ents) * nents;

	if (fence)
		virtio_gpu_fence_emit(vgdev, &cmd_p->hdr, fence);
	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
}

static void virtio_gpu_cmd_get_display_info_cb(struct virtio_gpu_device *vgdev,
					       struct virtio_gpu_vbuffer *vbuf)
{
	struct virtio_gpu_resp_display_info *resp =
		(struct virtio_gpu_resp_display_info *)vbuf->resp_buf;
	int i;

	spin_lock(&vgdev->display_info_lock);
	for (i = 0; i < vgdev->num_scanouts; i++) {
		vgdev->outputs[i].info = resp->pmodes[i];
		if (resp->pmodes[i].enabled) {
			DRM_DEBUG("output %d: %dx%d+%d+%d", i,
				  le32_to_cpu(resp->pmodes[i].r.width),
				  le32_to_cpu(resp->pmodes[i].r.height),
				  le32_to_cpu(resp->pmodes[i].r.x),
				  le32_to_cpu(resp->pmodes[i].r.y));
		} else {
			DRM_DEBUG("output %d: disabled", i);
		}
	}

	vgdev->display_info_pending = false;
	spin_unlock(&vgdev->display_info_lock);
	wake_up(&vgdev->resp_wq);

	if (!drm_helper_hpd_irq_event(vgdev->ddev))
		drm_kms_helper_hotplug_event(vgdev->ddev);
}

int virtio_gpu_cmd_get_display_info(struct virtio_gpu_device *vgdev)
{
	struct virtio_gpu_ctrl_hdr *cmd_p;
	struct virtio_gpu_vbuffer *vbuf;
	void *resp_buf;

	resp_buf = kzalloc(sizeof(struct virtio_gpu_resp_display_info),
			   GFP_KERNEL);
	if (!resp_buf)
		return -ENOMEM;

	cmd_p = virtio_gpu_alloc_cmd_resp
		(vgdev, &virtio_gpu_cmd_get_display_info_cb, &vbuf,
		 sizeof(*cmd_p), sizeof(struct virtio_gpu_resp_display_info),
		 resp_buf);
	memset(cmd_p, 0, sizeof(*cmd_p));

	vgdev->display_info_pending = true;
	cmd_p->type = cpu_to_le32(VIRTIO_GPU_CMD_GET_DISPLAY_INFO);
	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
	return 0;
}

int virtio_gpu_object_attach(struct virtio_gpu_device *vgdev,
			     struct virtio_gpu_object *obj,
			     uint32_t resource_id,
			     struct virtio_gpu_fence **fence)
{
	struct virtio_gpu_mem_entry *ents;
	struct scatterlist *sg;
	int si;

	if (!obj->pages) {
		int ret;
		ret = virtio_gpu_object_get_sg_table(vgdev, obj);
		if (ret)
			return ret;
	}

	/* gets freed when the ring has consumed it */
	ents = kmalloc_array(obj->pages->nents,
			     sizeof(struct virtio_gpu_mem_entry),
			     GFP_KERNEL);
	if (!ents) {
		DRM_ERROR("failed to allocate ent list\n");
		return -ENOMEM;
	}

	for_each_sg(obj->pages->sgl, sg, obj->pages->nents, si) {
		ents[si].addr = cpu_to_le64(sg_phys(sg));
		ents[si].length = cpu_to_le32(sg->length);
		ents[si].padding = 0;
	}

	virtio_gpu_cmd_resource_attach_backing(vgdev, resource_id,
					       ents, obj->pages->nents,
					       fence);
	obj->hw_res_handle = resource_id;
	return 0;
}

void virtio_gpu_cursor_ping(struct virtio_gpu_device *vgdev,
			    struct virtio_gpu_output *output)
{
	struct virtio_gpu_vbuffer *vbuf;
	struct virtio_gpu_update_cursor *cur_p;

	output->cursor.pos.scanout_id = cpu_to_le32(output->index);
	cur_p = virtio_gpu_alloc_cursor(vgdev, &vbuf);
	memcpy(cur_p, &output->cursor, sizeof(output->cursor));
	virtio_gpu_queue_cursor(vgdev, vbuf);
}