RE: [PATCH v2 11/12] drm/virtio: implement context init: add virtio_gpu_fence_event

["Kasireddy, Vivek" <vivek.kasireddy@intel.com>]

Hi Gurchetan,

> 
> Similar to DRM_VMW_EVENT_FENCE_SIGNALED.  Sends a pollable event
> to the DRM file descriptor when a fence on a specific ring is
> signaled.
> 
> One difference is the event is not exposed via the UAPI -- this is
> because host responses are on a shared memory buffer of type
> BLOB_MEM_GUEST [this is the common way to receive responses with
> virtgpu].  As such, there is no context specific read(..)
> implementation either -- just a poll(..) implementation.
[Kasireddy, Vivek] Given my limited understanding of virtio_gpu 3D/Virgl, I am
wondering why you'd need a new internal event associated with a fence; would
you not be able to accomplish the same by adding the out_fence_fd (from execbuf)
to your userspace's event loop (in addition to DRM fd) and get signalled?

Thanks,
Vivek

> 
> Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
> Acked-by: Nicholas Verne <nverne@chromium.org>
> ---
>  drivers/gpu/drm/virtio/virtgpu_drv.c   | 43 +++++++++++++++++++++++++-
>  drivers/gpu/drm/virtio/virtgpu_drv.h   |  7 +++++
>  drivers/gpu/drm/virtio/virtgpu_fence.c | 10 ++++++
>  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 34 ++++++++++++++++++++
>  4 files changed, 93 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
> index 9d963f1fda8f..749db18dcfa2 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_drv.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
> @@ -29,6 +29,8 @@
>  #include <linux/module.h>
>  #include <linux/console.h>
>  #include <linux/pci.h>
> +#include <linux/poll.h>
> +#include <linux/wait.h>
> 
>  #include <drm/drm.h>
>  #include <drm/drm_aperture.h>
> @@ -155,6 +157,35 @@ static void virtio_gpu_config_changed(struct virtio_device
> *vdev)
>  	schedule_work(&vgdev->config_changed_work);
>  }
> 
> +static __poll_t virtio_gpu_poll(struct file *filp,
> +				struct poll_table_struct *wait)
> +{
> +	struct drm_file *drm_file = filp->private_data;
> +	struct virtio_gpu_fpriv *vfpriv = drm_file->driver_priv;
> +	struct drm_device *dev = drm_file->minor->dev;
> +	struct drm_pending_event *e = NULL;
> +	__poll_t mask = 0;
> +
> +	if (!vfpriv->ring_idx_mask)
> +		return drm_poll(filp, wait);
> +
> +	poll_wait(filp, &drm_file->event_wait, wait);
> +
> +	if (!list_empty(&drm_file->event_list)) {
> +		spin_lock_irq(&dev->event_lock);
> +		e = list_first_entry(&drm_file->event_list,
> +				     struct drm_pending_event, link);
> +		drm_file->event_space += e->event->length;
> +		list_del(&e->link);
> +		spin_unlock_irq(&dev->event_lock);
> +
> +		kfree(e);
> +		mask |= EPOLLIN | EPOLLRDNORM;
> +	}
> +
> +	return mask;
> +}
> +
>  static struct virtio_device_id id_table[] = {
>  	{ VIRTIO_ID_GPU, VIRTIO_DEV_ANY_ID },
>  	{ 0 },
> @@ -194,7 +225,17 @@ MODULE_AUTHOR("Dave Airlie <airlied@redhat.com>");
>  MODULE_AUTHOR("Gerd Hoffmann <kraxel@redhat.com>");
>  MODULE_AUTHOR("Alon Levy");
> 
> -DEFINE_DRM_GEM_FOPS(virtio_gpu_driver_fops);
> +static const struct file_operations virtio_gpu_driver_fops = {
> +	.owner          = THIS_MODULE,
> +	.open           = drm_open,
> +	.release        = drm_release,
> +	.unlocked_ioctl = drm_ioctl,
> +	.compat_ioctl   = drm_compat_ioctl,
> +	.poll           = virtio_gpu_poll,
> +	.read           = drm_read,
> +	.llseek         = noop_llseek,
> +	.mmap           = drm_gem_mmap
> +};
> 
>  static const struct drm_driver driver = {
>  	.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_RENDER |
> DRIVER_ATOMIC,
> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
> index cb60d52c2bd1..e0265fe74aa5 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_drv.h
> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
> @@ -138,11 +138,18 @@ struct virtio_gpu_fence_driver {
>  	spinlock_t       lock;
>  };
> 
> +#define VIRTGPU_EVENT_FENCE_SIGNALED_INTERNAL 0x10000000
> +struct virtio_gpu_fence_event {
> +	struct drm_pending_event base;
> +	struct drm_event event;
> +};
> +
>  struct virtio_gpu_fence {
>  	struct dma_fence f;
>  	uint32_t ring_idx;
>  	uint64_t fence_id;
>  	bool emit_fence_info;
> +	struct virtio_gpu_fence_event *e;
>  	struct virtio_gpu_fence_driver *drv;
>  	struct list_head node;
>  };
> diff --git a/drivers/gpu/drm/virtio/virtgpu_fence.c
> b/drivers/gpu/drm/virtio/virtgpu_fence.c
> index 98a00c1e654d..f28357dbde35 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_fence.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_fence.c
> @@ -152,11 +152,21 @@ void virtio_gpu_fence_event_process(struct virtio_gpu_device
> *vgdev,
>  				continue;
> 
>  			dma_fence_signal_locked(&curr->f);
> +			if (curr->e) {
> +				drm_send_event(vgdev->ddev, &curr->e->base);
> +				curr->e = NULL;
> +			}
> +
>  			list_del(&curr->node);
>  			dma_fence_put(&curr->f);
>  		}
> 
>  		dma_fence_signal_locked(&signaled->f);
> +		if (signaled->e) {
> +			drm_send_event(vgdev->ddev, &signaled->e->base);
> +			signaled->e = NULL;
> +		}
> +
>  		list_del(&signaled->node);
>  		dma_fence_put(&signaled->f);
>  		break;
> diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> index be7b22a03884..fdaa7f3d9eeb 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> @@ -38,6 +38,36 @@
>  				    VIRTGPU_BLOB_FLAG_USE_SHAREABLE | \
>  				    VIRTGPU_BLOB_FLAG_USE_CROSS_DEVICE)
> 
> +static int virtio_gpu_fence_event_create(struct drm_device *dev,
> +					 struct drm_file *file,
> +					 struct virtio_gpu_fence *fence,
> +					 uint32_t ring_idx)
> +{
> +	struct virtio_gpu_fpriv *vfpriv = file->driver_priv;
> +	struct virtio_gpu_fence_event *e = NULL;
> +	int ret;
> +
> +	if (!(vfpriv->ring_idx_mask & (1 << ring_idx)))
> +		return 0;
> +
> +	e = kzalloc(sizeof(*e), GFP_KERNEL);
> +	if (!e)
> +		return -ENOMEM;
> +
> +	e->event.type = VIRTGPU_EVENT_FENCE_SIGNALED_INTERNAL;
> +	e->event.length = sizeof(e->event);
> +
> +	ret = drm_event_reserve_init(dev, file, &e->base, &e->event);
> +	if (ret)
> +		goto free;
> +
> +	fence->e = e;
> +	return 0;
> +free:
> +	kfree(e);
> +	return ret;
> +}
> +
>  /* Must be called with &virtio_gpu_fpriv.struct_mutex held. */
>  static void virtio_gpu_create_context_locked(struct virtio_gpu_device *vgdev,
>  					     struct virtio_gpu_fpriv *vfpriv)
> @@ -195,6 +225,10 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev,
> void *data,
>  		goto out_unresv;
>  	}
> 
> +	ret = virtio_gpu_fence_event_create(dev, file, out_fence, ring_idx);
> +	if (ret)
> +		goto out_unresv;
> +
>  	if (out_fence_fd >= 0) {
>  		sync_file = sync_file_create(&out_fence->f);
>  		if (!sync_file) {
> --
> 2.33.0.464.g1972c5931b-goog