[virtio-dev] Re: [PATCH v7 4/4] transport-pci: Introduce group legacy group member config region access

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jun 28, 2023 at 12:10:50AM +0300, Parav Pandit wrote:
> This patch links how in a PCI transport a group owner can access group
> member (PCI VFs) legacy registers using a legacy registers access
> commands using administration virtqueue infrastructure.
> 
> Additionally it extend the PCI notification capability through which a
> PCI VF device indicates to the driver which PCI BAR region to be used
> for driver notifications.
> 
> Fixes: https://github.com/oasis-tcs/virtio-spec/issues/167
> Signed-off-by: Parav Pandit <parav@nvidia.com>
> ---
> changelog:
> v6->v7:
> - addressed comments from Michael
> - removed driver normative about I/O BAR emulation as it does not
>   make much sense for the spec
> - removed references to administration virtqueue
> - rewrote driver legacy region access without guest and hypervisor
>   wording
> - added normative for notification region
> - added normative for PCI IDs for device which support legacy commands
> v5->v6:
> - aligned pci capability to 4B as required by PCI spec
> - added text for the PCI capability for the group member device
> v4->v5:
> - split pci transport and generic command section to new patch
> - removed multiple references to the VF
> - written the description of the command as generic with member
>   and group device terminology
> - reflected many section names to remove VF
> v3->v4:
> - moved noted to the conformance section details in next patch
> - removed queue notify address query AQ command on Michael's suggestion,
>   though it is fine. Instead replaced with extending virtio_pci_notify_cap
>   to indicate that legacy queue notifications can be done on the
>   notification location.
> - fixed spelling errors.
> - replaced administrative virtqueue to administration virtqueue
> - added queue notification capability register to indicate legacy q
>   notification supported
> v2->v3:
> - adddressed Jason and Michael's comment to split single register
>   access command to common config and device specific commands.
> - dropped the suggetion to introduce enable/disable command as
>   admin command cap bit already covers it.
> v1->v2:
> - addressed comments from Michael
> - added theory of operation
> - grammar corrections
> - removed group fields description from individual commands as
>   it is already present in generic section
> - added endianness normative for legacy device registers region
> - renamed the file to drop vf and add legacy prefix
> 
> - added overview in commit log
> - renamed subsection to reflect command
> ---
>  conformance.tex               |  1 +
>  transport-pci-legacy-regs.tex | 43 +++++++++++++++++++++++++++++++++++
>  transport-pci.tex             |  2 ++
>  3 files changed, 46 insertions(+)
>  create mode 100644 transport-pci-legacy-regs.tex
> 
> diff --git a/conformance.tex b/conformance.tex
> index dc00e84..b3f2c92 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -267,6 +267,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item Section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Legacy Interfaces: A Note on PCI Device Layout}
>  \item Section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Virtio Device Configuration Layout Detection / Legacy Interface: A Note on Device Layout Detection}
>  \item Section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Virtqueue Configuration / Legacy Interface: A Note on Virtqueue Configuration}
> +\item Section \ref{devicenormative:Virtio Transport Options / Virtio Over PCI Bus / Legacy Interface: Group Member Device Configuration Region Access}
>  \item Section \ref{sec:Virtio Transport Options / Virtio Over MMIO / Legacy interface}
>  \item Section \ref{sec:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Setting the Virtio Revision / Legacy Interfaces: A Note on Setting the Virtio Revision}
>  \item Section \ref{sec:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Configuring a Virtqueue / Legacy Interface: A Note on Configuring a Virtqueue}
> diff --git a/transport-pci-legacy-regs.tex b/transport-pci-legacy-regs.tex
> new file mode 100644
> index 0000000..9559768
> --- /dev/null
> +++ b/transport-pci-legacy-regs.tex
> @@ -0,0 +1,43 @@
> +\subsection{Legacy Interface: Group member device Configuration Region Access}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / Legacy Interface: Group Member Device Configuration Region Access}
> +
> +The PCI owner device or the member device or both supports driver notifications using
> +a notification region defined in the \field{struct virtio_pci_notify_region}.
> +
> +In \field{struct virtio_virtio_admin_cmd_legacy_notify_query_entry},
> +\field{region} is defined as following:
> +
> +\begin{lstlisting}
> +struct virtio_pci_notify_region {
> +        u8 owner;    /* When set to 1, notification region of the owner device */
> +        u8 bar;    /* BAR of the member or owner device */
> +        u8 padding[2];
> +        le32 offset; /* Offset within bar. */
> +};
> +\end{lstlisting}

Is this just a legacy thing or somehow generic? If the former please
stick _legacy_ in the struct name.


> +
> +The group owner device hardwire VF BAR0 in the SR-IOV Extended capability.
> +
> +The group member device does not use PCI BAR0 in various PCI capabilities.

what does this mean? what various capabilities? VFs don't have PCI BAR0
at all ... 

> +
> +\devicenormative{\subsubsection}{Legacy Interface: Group Member Device Legacy Configuration Region Access}{Virtio Transport Options / Virtio Over PCI Bus / Legacy Interface: Group Member Device Configuration Region Access}
> +
> +When a PCI SR-IOV group owner device supports
> +VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_READ,
> +VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_WRITE, VIRTIO_ADMIN_CMD_LEGACY_DEV_CFG_READ,
> +VIRTIO_ADMIN_CMD_LEGACY_DEV_CFG_WRITE commands, the group owner device MUST
> +hardwire VF BAR0 in the SR-IOV Extended capability and the group member device
> +MUST NOT use BAR0 in any of the Virtio Structure PCI Capabilities.
> +
> +The group member driver SHOULD use the notification region supplied by the group
> +owner driver.
> +
> +The group owner device or the group member device or both MAY support driver
> +notifications region.

why is this text here as opposed to the other file?
But really I think for now it's easier to just have everything in
admin-cmds-legacy-interface.tex

> +
> +For the SR-IOV group type, the owner device supporting
> +VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_READ,
> +VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_WRITE, VIRTIO_ADMIN_CMD_LEGACY_DEV_CFG_READ,
> +VIRTIO_ADMIN_CMD_LEGACY_DEV_CFG_WRITE and VIRTIO_ADMIN_CMD_LEGACY_NOTIFY_QUERY
> +commands and its member device SHOULD follow the rules for the PCI Device ID,
> +Revision ID and Subsystem Device ID of the non-transitional devices documented in
> +section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Discovery}.
> diff --git a/transport-pci.tex b/transport-pci.tex
> index a5c6719..72c78f6 100644
> --- a/transport-pci.tex
> +++ b/transport-pci.tex
> @@ -1212,3 +1212,5 @@ \subsubsection{Driver Handling Interrupts}\label{sec:Virtio Transport Options /
>          re-examine the configuration space to see what changed.
>      \end{itemize}
>  \end{itemize}
> +
> +\input{transport-pci-legacy-regs.tex}
> -- 
> 2.26.2


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