Re: [PATCH vhost next 10/10] vdpa/mlx5: Add VDPA driver for supported mlx5 devices

[Jason Wang]

On 2020/7/19 äå3:49, Eli Cohen wrote:
> On Fri, Jul 17, 2020 at 04:57:29PM +0800, Jason Wang wrote:
> > > Looks like checking intialized is enough. Will fix this.
> > > > > +
> > > > > +static void mlx5_vdpa_set_vq_ready(struct vdpa_device *vdev, u16 idx, bool ready)
> > > > > +{
> > > > > +	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
> > > > > +	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
> > > > > +	struct mlx5_vdpa_virtqueue *mvq = &ndev->vqs[idx];
> > > > > +	int err;
> > > > > +
> > > > > +	if (!mvq->ready && ready && mvq->fw_state != MLX5_VIRTIO_NET_Q_OBJECT_STATE_RDY) {
> > > > > +		err = modify_virtqueue(ndev, mvq, MLX5_VIRTIO_NET_Q_OBJECT_STATE_RDY);
> > > > > +		if (err) {
> > > > > +			mlx5_vdpa_warn(mvdev, "failed to modify virtqueue(%d)\n", err);
> > > > > +			return;
> > > > > +		}
> > > > > +	}
> > > > I wonder what's the reason of changing vq state on the hardware
> > > > here. I think we can defer it to set_status().
> > > I can defer this to set status.
> > >
> > > I just wonder if it is possible that the core vdpa driver may call this
> > > function with ready equals false and after some time call it with ready
> > > equals true.
> >
> > Good point, so I think we can keep the logic. But looks like the
> > code can not work if ready equals false since it only tries to
> > modify vq state to RDY.
> The point is that you cannot modify the virtqueue to "not ready".


Is this a hardware limitation of software one?

I'm asking since we need support live migration. But a questions is how 
to stop the device but not reset, since we need get e.g last_avail_idx 
from the device.

It could be either:

1) set_status(0)
2) get_vq_state()

or

1) set_queue_ready(0)
2) get_vq_state()

Set_status(0) means reset the virtio device but last_avail_idx is 
something out of virtio spec. I guess using set_queue_ready() is better.

What's you opinion?

Thanks


>   The
> only option is to destroy it and create a new one. This means that if I
> get ready equals false after the virtqueue has been created I need to
> teardown the driver and set it up again.
>
> Given that, I think your original suggestion to defer this logic is
> reasonable.