Re: [virtio-comment] [PATCH v4] clarify device reset

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 5 May 2021 09:20:45 -0400
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Thu, Jan 28, 2021 at 02:52:35PM +0100, Cornelia Huck wrote:
> > Properly specify that the method for the driver to request a
> > device reset is transport specific, and some action the device
> > has to take.
> > 
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> > 
> > Stefan, Halil: I did not apply your R-b due to the amount of changes.
> > 
> > v3 -> v4:
> >   - moved device status 're-initialize to 0' clause that is now duplicated
> >     to an informal description
> >   - more clarifications on when reset may be used and device requirements
> >   - use \field{device status} consistently
> > RFC v2 -> v3:
> >   - re-worded the "must not send notifications" clause to avoid guessing
> >   - added a driver conformance clause on how a driver should find out
> >     when reset is complete
> > RFC -> RFC v2:
> >   - moved reset spec to basic facilities
> > 
> > ---
> >  conformance.tex |  2 ++
> >  content.tex     | 24 +++++++++++++++++++++++-
> >  2 files changed, 25 insertions(+), 1 deletion(-)
> > 

(...)

> > diff --git a/content.tex b/content.tex
> > index 1ca24c13f2d0..47239b877c6c 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -51,6 +51,9 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> >    an error from which it can't recover.
> >  \end{description}
> >  
> > +The \field{device status} field starts out as 0, and is reinitialized to 0 by
> > +the device during reset.
> > +
> >  \drivernormative{\subsection}{Device Status Field}{Basic Facilities of a Virtio Device / Device Status Field}
> >  The driver MUST update \field{device status},
> >  setting bits to indicate the completed steps of the driver
> > @@ -71,7 +74,6 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> >  \end{note}
> >  
> >  \devicenormative{\subsection}{Device Status Field}{Basic Facilities of a Virtio Device / Device Status Field}
> > -The device MUST initialize \field{device status} to 0 upon reset.
> >  
> >  The device MUST NOT consume buffers or send any used buffer
> >  notifications to the driver before DRIVER_OK.  
> 
> Do we want to keep the part where it starts out as 0 here?

Wouldn't that duplicate the statement in the 'Device Reset' normative
section below?

> 
> > @@ -193,6 +195,26 @@ \section{Notifications}\label{sec:Basic Facilities of a Virtio Device
> >  terminology. Occasionally, the term event is used to refer to
> >  a notification or a receipt of a notification.
> >  
> > +\section{Device Reset}\label{sec:Basic Facilities of a Virtio Device / Device Reset}
> > +
> > +The driver may want to initiate a device reset at various times; notably,
> > +it is required to do so during device initialization and device cleanup.
> > +
> > +The mechanism used by the driver to initiate the reset is transport specific.
> > +
> > +\devicenormative{\subsection}{Device Reset}{Basic Facilities of a Virtio Device / Device Reset}
> > +
> > +A device MUST reinitialize \field{device status} to 0 after receiving a reset.
> > +
> > +A device MUST NOT send notifications or interact with the queues after
> > +indicating completion of the reset by reinitializing \field{device status}
> > +to 0, until the driver re-initializes the device.
> > +
> > +\drivernormative{\subsection}{Device Reset}{Basic Facilities of a Virtio Device / Device Reset}
> > +
> > +The driver SHOULD consider a driver-initiated reset complete when it
> > +reads \field{device status} as 0.
> > +
> >  \section{Device Configuration Space}\label{sec:Basic Facilities of a Virtio Device / Device Configuration Space}
> >  
> >  Device configuration space is generally used for rarely-changing or