Re: [PATCH v5 5/7] Add miscellaneous configuration structure for PCI

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

On Wed, Apr 27, 2022 at 01:58:22AM +0300, Max Gurtovoy wrote:
> This new structure will be used for adding new miscellaneous registers
> for a virtio device configuration layout.
> 
> For now, only admin_queue_index register is added. Admin virtqueue index
> does not depend on the device type. Hence, add a PCI capability to read
> the admin virtqueue index.
> 
> Reviewed-by: Parav Pandit <parav@nvidia.com>
> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>


I guess we discussed this but I forgot. Why do we have this new
structure as opposed to just adding the value at the end of config
structure? I was kind of hoping that the structure can be
reused for CCW/MMIO and then we can add more use-cases with
new transport and device independent structures.

If we keep it transport specific I don't really understand why
is it useful ...

> ---
>  conformance.tex |  2 ++
>  content.tex     | 29 +++++++++++++++++++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/conformance.tex b/conformance.tex
> index 3c7b7bc..c183581 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -103,6 +103,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{drivernormative:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / PCI configuration access capability}
>  \item \ref{drivernormative:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / MSI-X Vector Configuration}
>  \item \ref{drivernormative:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Notification of Device Configuration Changes}
> +\item \ref{drivernormative:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Miscellaneous configuration structure layout}
>  \end{itemize}
>  
>  \conformance{\subsection}{MMIO Driver Conformance}\label{sec:Conformance / Driver Conformance / MMIO Driver Conformance}
> @@ -364,6 +365,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{devicenormative:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / MSI-X Vector Configuration}
>  \item \ref{devicenormative:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Used Buffer Notifications}
>  \item \ref{devicenormative:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Notification of Device Configuration Changes}
> +\item \ref{devicenormative:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Miscellaneous configuration structure layout}
>  \end{itemize}
>  
>  \conformance{\subsection}{MMIO Device Conformance}\label{sec:Conformance / Device Conformance / MMIO Device Conformance}
> diff --git a/content.tex b/content.tex
> index 163cb34..0c1d44f 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -712,6 +712,7 @@ \subsection{Virtio Structure PCI Capabilities}\label{sec:Virtio Transport Option
>  \item ISR Status
>  \item Device-specific configuration (optional)
>  \item PCI configuration access
> +\item Miscellaneous configuration
>  \end{itemize}
>  
>  Each structure can be mapped by a Base Address register (BAR) belonging to
> @@ -771,6 +772,8 @@ \subsection{Virtio Structure PCI Capabilities}\label{sec:Virtio Transport Option
>  #define VIRTIO_PCI_CAP_SHARED_MEMORY_CFG 8
>  /* Vendor-specific data */
>  #define VIRTIO_PCI_CAP_VENDOR_CFG        9
> +/* Miscellaneous configuration */
> +#define VIRTIO_PCI_CAP_MISC_CFG          10
>  \end{lstlisting}
>  
>          Any other value is reserved for future use.
> @@ -1352,6 +1355,32 @@ \subsubsection{PCI configuration access capability}\label{sec:Virtio Transport O
>  specified by some other Virtio Structure PCI Capability
>  of type other than \field{VIRTIO_PCI_CAP_PCI_CFG}.
>  
> +\subsubsection{Miscellaneous configuration structure layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Miscellaneous configuration structure layout}
> +
> +The miscellaneous configuration structure is found at the bar and offset within the VIRTIO_PCI_CAP_MISC_CFG capability.

If this is all there is going to be there, maybe just stick the value in
the capability directly.

> +Its layout is below.
> +\begin{lstlisting}
> +struct virtio_pci_misc_cfg {
> +        le16 admin_queue_index;         /* read-only for driver */
> +};
> +\end{lstlisting}
> +
> +\begin{description}
> +\item[\field{admin_queue_index}]
> +        The device uses this to report the index of the admin virtqueue.
> +        This field is valid only if VIRTIO_F_ADMIN_VQ is set.
> +\end{description}
> +


we need to explain that we will add more fields and drivers must
not make assumptions that this structure is 2 bytes in size.
look for a language like this in device specific and common
structures.

> +\devicenormative{\paragraph}{Miscellaneous configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Miscellaneous configuration structure layout}
> +The device MUST present VIRTIO_PCI_CAP_MISC_CFG capability when VIRTIO_F_ADMIN_VQ is set.
> +
> +The device MUST present a valid \field{admin_queue_index} when VIRTIO_F_ADMIN_VQ is set.
> +
> +\drivernormative{\paragraph}{Miscellaneous configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Miscellaneous configuration structure layout}
> +The driver MUST NOT proceed with configuring the admin virtqueue in case VIRTIO_F_ADMIN_VQ is set and VIRTIO_PCI_CAP_MISC_CFG capability is not present.
> +
> +The driver MUST use the value of \field{admin_queue_index} to configure the admin virtqueue. For more details on virtqueue configuration see section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Virtqueue Configuration}.
> +
>  \subsubsection{Legacy Interfaces: A Note on PCI Device Layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Legacy Interfaces: A Note on PCI Device Layout}
>  
>  Transitional devices MUST present part of configuration
> -- 
> 2.21.0