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

[Srivatsa Vaddagiri <svaddagi@qti.qualcomm.com>]

> On Mon, Jul 26, 2021 at 01:36:56PM +0200, Cornelia Huck wrote:

> > On Mon, Jul 26 2021, Srivatsa Vaddagiri <svaddagi@qti.qualcomm.com> wrote:

> >

> > >> > +indicated by a read of \field{Status} returning 0. Such a device MUST also

> > >> > fail to accept

> > >> > +FEATURES_OK bit if driver does not negotiate VIRTIO_F_MMIO_RESET_WAIT.

> > >>

> > >> So, this basically means that an older driver that does not know the new

> > >> feature bit will not work with devices offering this bit, even if it did

> > >> poll? This seems acceptable, I just wanted to spell it out.

> > >

> > > Yes I believe that's the desired result. Device has no way to know if driver

> > > will poll for reset completion or not unless it accepts the feature.

> > > Are you suggesting we explicitly put in some text in spec to that

> > > effect?

> >

> > Not sure whether it is needed (do others have an opinion?), but probably

> > not.

>

> What about resets before FEATURES_OK? How are these handled?

From device perspective, it's reset logic will always be same, independent of

when reset was performed by driver (before or after feature negotiation). A

driver that does not wait for reset completion will see undefined behavior after

reset until it discovers that feature negotiation has failed?

- vatsa

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