From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-comment-return-1647-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 73F67985F3E for ; Tue, 19 Jan 2021 02:40:23 +0000 (UTC) Date: Tue, 19 Jan 2021 03:40:08 +0100 From: Halil Pasic Message-ID: <20210119034008.735f80ad.pasic@linux.ibm.com> In-Reply-To: <20210118164132.GC9899@work-vm> References: <20210118163804.437098-1-cohuck@redhat.com> <20210118164132.GC9899@work-vm> MIME-Version: 1.0 Subject: Re: [virtio-comment] [PATCH RFC v2] clarify device reset Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable To: "Dr. David Alan Gilbert" Cc: Cornelia Huck , virtio-comment@lists.oasis-open.org, Jason Wang List-ID: On Mon, 18 Jan 2021 16:41:32 +0000 "Dr. David Alan Gilbert" 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. > >=20 > > Signed-off-by: Cornelia Huck > > --- > >=20 > > RFC -> RFC v2: > > - moved reset spec to basic facilities > >=20 > > --- > > conformance.tex | 1 + > > content.tex | 13 +++++++++++++ > > 2 files changed, 14 insertions(+) > >=20 > > 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 / Devic= e Status Field} > > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Featu= re Bits} > > +\item \ref{devicenormative:Basic Facilities of a Virtio Device / Devic= e Reset} > > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Devic= e Configuration Space} > > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Messa= ge Framing} > > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Virtq= ueues / 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. > > =20 > > +\section{Device Reset}\label{sec:Basic Facilities of a Virtio Device /= Device Reset} > > + > > +The driver may initiate a device reset at various times; notably, duri= ng > > +device initialization and device cleanup. > > + > > +The mechanism used by the driver to initiate the reset is transport sp= ecific. > > + > > +\devicenormative{\subsection}{Device Reset}{Basic Facilities of a Virt= io 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/ =20 >=20 > 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.=20 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."=20 (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#x= 1-1090004) 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. Of course tying this kind of sequencing (happens-before) to the receiving of a reset does not work. I agree with that to the fullest. Regards, Halil This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lis= ts Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/