Re: [PATCH V2 3/4] vp_vdpa: allow set vq state to initial state after reset

[Jason Wang]

在 2021/6/2 下午2:13, Eli Cohen 写道:
> On Wed, Jun 02, 2021 at 10:10:42AM +0800, Jason Wang wrote:
> > We used to fail the set_vq_state() since it was not supported yet by
> > the virtio spec. But if the bus tries to set the state which is equal
> > to the device initial state after reset, we can let it go.
> >
> > This is a must for virtio_vdpa() to set vq state during probe which is
> > required for some vDPA parents.
> >
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> >   drivers/vdpa/virtio_pci/vp_vdpa.c | 42 ++++++++++++++++++++++++++++---
> >   1 file changed, 39 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c b/drivers/vdpa/virtio_pci/vp_vdpa.c
> > index c76ebb531212..18bf4a422772 100644
> > --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
> > +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
> > @@ -210,13 +210,49 @@ static int vp_vdpa_get_vq_state(struct vdpa_device *vdpa, u16 qid,
> >   	return -EOPNOTSUPP;
> >   }
> >   
> > +static int vp_vdpa_set_vq_state_split(struct vdpa_device *vdpa,
> > +				      const struct vdpa_vq_state *state)
> > +{
> > +	const struct vdpa_vq_state_split *split = &state->split;
> > +
> > +	if (split->avail_index == 0)
> > +		return 0;
> > +
> > +	return -EOPNOTSUPP;
> > +}
> > +
> > +static int vp_vdpa_set_vq_state_packed(struct vdpa_device *vdpa,
> > +				       const struct vdpa_vq_state *state)
> > +{
> > +	const struct vdpa_vq_state_packed *packed = &state->packed;
> > +
> > +	if (packed->last_avail_counter == 1 &&
> Can you elaborate on the requirement on last_avail_counter and
> last_used_counter?


This is required by the virtio spec:

"
2.7.1 Driver and Device Ring Wrap Counters
Each of the driver and the device are expected to maintain, internally, 
a single-bit ring wrap counter initialized to 1.
"

For virtio-pci device, since there's no way to assign the value of those 
counters, the counters will be reset to 1 after reset, otherwise the 
driver can't work.

Thanks


> > +	    packed->last_avail_idx == 0 &&
> > +	    packed->last_used_counter == 1 &&
> > +	    packed->last_used_idx == 0)
> > +		return 0;
> > +
> > +	return -EOPNOTSUPP;
> > +}
> > +
> >   static int vp_vdpa_set_vq_state(struct vdpa_device *vdpa, u16 qid,
> >   				const struct vdpa_vq_state *state)
> >   {
> > -	/* Note that this is not supported by virtio specification, so
> > -	 * we return -ENOPOTSUPP here. This means we can't support live
> > -	 * migration, vhost device start/stop.
> > +	struct virtio_pci_modern_device *mdev = vdpa_to_mdev(vdpa);
> > +
> > +	/* Note that this is not supported by virtio specification.
> > +	 * But if the state is by chance equal to the device initial
> > +	 * state, we can let it go.
> >   	 */
> > +	if ((vp_modern_get_status(mdev) & VIRTIO_CONFIG_S_FEATURES_OK) &&
> > +	    !vp_modern_get_queue_enable(mdev, qid)) {
> > +		if (vp_modern_get_driver_features(mdev) &
> > +		    BIT_ULL(VIRTIO_F_RING_PACKED))
> > +			return vp_vdpa_set_vq_state_packed(vdpa, state);
> > +		else
> > +			return vp_vdpa_set_vq_state_split(vdpa,	state);
> > +	}
> > +
> >   	return -EOPNOTSUPP;
> >   }
> >   
> > --
> > 2.25.1