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

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 28 Jan 2021 14:52:35 +0100
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.

Fixes: https://github.com/oasis-tcs/virtio-spec/issues/93

> 
> 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/conformance.tex b/conformance.tex
> index e78adfdbd283..17c390d249db 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -64,6 +64,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \begin{itemize}
>  \item \ref{drivernormative:Basic Facilities of a Virtio Device / Device Status Field}
>  \item \ref{drivernormative:Basic Facilities of a Virtio Device / Feature Bits}
> +\item \ref{drivernormative:Basic Facilities of a Virtio Device / Device Reset}
>  \item \ref{drivernormative:Basic Facilities of a Virtio Device / Device Configuration Space}
>  \item \ref{drivernormative:Basic Facilities of a Virtio Device / Virtqueues}
>  \item \ref{drivernormative:Basic Facilities of a Virtio Device / Message Framing}
> @@ -283,6 +284,7 @@ \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 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.
> @@ -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


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