Re: [PATCH V2 2/2] virtio: introduce STOP status bit

[Jason Wang <jasowang@redhat.com>]

å 2021/7/8 äå12:45, Cornelia Huck åé:
> On Wed, Jul 07 2021, Jason Wang <jasowang@redhat.com> wrote:
>
> > å 2021/7/6 äå10:27, Cornelia Huck åé:
> > > On Tue, Jul 06 2021, Jason Wang <jasowang@redhat.com> wrote:
> > >
> > > > å 2021/7/6 äå8:50, Cornelia Huck åé:
> > > > > On Tue, Jul 06 2021, Jason Wang <jasowang@redhat.com> wrote:
> > > > > > +If VIRTIO_F_STOP has been negotiated, to stop a device, after setting
> > > > > > +STOP, the driver MUST re-read the device status to ensure the STOP bit
> > > > > > +is set to synchronize with the device.
> > > > > Is this more that the driver needs to re-read the status until STOP is
> > > > > set to make sure that the stop process has finished?
> > > > Yes.
> > > >
> > > >
> > > > >     If the device has
> > > > > offered the feature and the driver accepted it, I'd assume that the
> > > > > device will eventually finish with the procedure, or sets NEEDS_RESET if
> > > > > something goes wrong?
> > > > As stated below, the device must either:
> > > >
> > > > 1) finish all pending requests
> > > >
> > > > or
> > > >
> > > > 2) provide a device specific way for the driver to save and restore
> > > > pending requests
> > > >
> > > > before setting STOP.
> > > >
> > > > Otherwise the device can't offer this feature.
> > > >
> > > > Using NEEDS_RESET seems more complicated than this.
> > > Hm, what happens on an internal error?
> >
> > A question, can reset fail? If yes, do we need to define how to proceed
> > in the driver side?
> >
> > If not, I don't need the reason we need to deal with that in the STOP.
> When you put it that way, it makes sense. Let's just keep it simple,
> then.


I agree and according to the spec, reset should succeed, since it was 
used to recover from NEEDS_RESET:

"""

The driver SHOULD NOT rely on completion of operations of a device if 
DEVICE_NEEDS_RESET is set. Note: For example, the driver canât assume 
requests in flight will be completed if DEVICE_NEEDS_RESET is set, nor 
can it assume that they have not been completed. A good implementation 
will try to recover by issuing a reset.

"""

Thanks


>