Re: [virtio-dev] Re: [PATCH v1] virtio-mmio: Specify wait needed in driver during reset

[Jason Wang <jasowang@redhat.com>]

On Wed, Aug 18, 2021 at 1:51 PM Srivatsa Vaddagiri
<quic_svaddagi@quicinc.com> wrote:
>
> * Jason Wang <jasowang@redhat.com> [2021-08-18 13:40:45]:
>
> > > Hmm ..are you suggesting that we read the Version register as part of reset code
> > > and do the wait part only for v3 device?
> >
> > We only need to read the version once (see virtio_mmio_probe()). So it
>
> Ok sorry saw that now.
>
> > could be something like
> >
> > if (vm_dev->version == 0x3) {
> >     while (readl(vm_dev->base + VIRTIO_MMIO_STATUS))
> >         msleep(1);
> > }
> >
> > > Otherwise we have the same issue as
> > > feature bit with version change also.
> > >
> > > Can't the driver do the same with feature register also? Do poll if
> > > WAIT_FOR_RESET_COMPLETION feature bit is set, which can happen before feature
> > > negotiation is complete.
> >
> > The possible issue is that the feature negotiation is not done at that time.
>
> Fine let me take a stab at the next version which will have this:
>
> * Introduce a status bit for device to indicate "reset in progress". This could
>   be adopted by other transports also (for ex PCI).

I may miss something discussion but any reason that the current
VIRTIO_MMIO_STATUS is not sufficient?

>
> * For v3 MMIO devices, driver, after initiating reset, should wait until
>   status = 0 or device indicates "failure". What the driver does when it sees
>   failure can be implementation defined (it can give up or try reset few more
>   times)

Yes, but let's wait a little bit to see if it is agreed by others.

Thanks

>
> - vatsa
>
> --
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>