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Subject: Re: [virtio-comment] [PATCH RFC v2] clarify device reset
On Tue, 19 Jan 2021 03:40:08 +0100 Halil Pasic <pasic@linux.ibm.com> wrote: > On Mon, 18 Jan 2021 16:41:32 +0000 > "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote: > > > * Cornelia Huck (cohuck@redhat.com) 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> > > > --- > > > > > > RFC -> RFC v2: > > > - moved reset spec to basic facilities > > > > > > --- > > > conformance.tex | 1 + > > > content.tex | 13 +++++++++++++ > > > 2 files changed, 14 insertions(+) > > > > > > diff --git a/conformance.tex b/conformance.tex > > > index eb3324053080..3be499ae3c5e 100644 > > > --- a/conformance.tex > > > +++ b/conformance.tex > > > @@ -271,6 +271,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets} > > > \begin{itemize} > > > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Device Status Field} > > > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Feature Bits} > > > +\item \ref{devicenormative:Basic Facilities of a Virtio Device / Device Reset} > > > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Device Configuration Space} > > > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Message Framing} > > > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Descriptor Table} > > > diff --git a/content.tex b/content.tex > > > index 620c0e28c9a7..782ddf3ed78d 100644 > > > --- a/content.tex > > > +++ b/content.tex > > > @@ -193,6 +193,19 @@ \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 initiate a device reset at various times; notably, 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 device status to 0 after receiving a reset. > > > + > > > +A device MUST NOT send notifications after receiving a reset. > > > + > > s/after receiving a reset/after presenting a 0 status, that indicates > the reset is done/ "A device MUST NOT send notifications after indicating completion of the reset by reinitializing the device status to 0." ? > > > > This feels like a bit of a race in the description; a Device may have > > just sent a notification at the point that it receives a reset. > > When a driver initiates a reset, how does the driver know that the > > device has received it? > > I agree, but with the proposed modification not any more. > > To answer your question: PCI has the following driver normative (which I > believe needs to be generalized so we have something similar for each > transport, and thus the same semantics): > "After writing 0 to device_status, the driver MUST wait for a read of > device_status to return 0 before reinitializing the device." > (4.1.4.3.2 Driver Requirements: Common configuration structure layout, > https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-1090004) > > In general, after asking for a reset, the driver should/must ensure that > the reset was performed by the device by reading a 0 status. If the > status is non-zero, the reset at the device may still be in progress. > IMHO we need another driver normative for that. "After the driver has initiated a reset of the device, it MUST NOT consider the reset to be completed if the device status is not 0." ? Maybe without the double negation. (We could consider the reset for ccw devices done once we get final status for the reset ccw. Would save the round trip for a read status ccw, but would also be different from the other transports.)
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