Re: [PATCH v12 05/10] pci: add admin vq registers to virtio over pci

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 24/04/2023 19:44, Michael S. Tsirkin wrote:
> Add new registers to the PCI common configuration structure.
>
> These registers will be used for querying the indices of the admin
> virtqueues of the owner device. To configure, reset or enable the admin
> virtqueues, the driver should follow existing queue configuration/setup
> sequence.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>
> ---
> dropped Max's S.O.B
> make queue_num not 0 based
>
> squash! pci: add admin vq registers to virtio over pci
>
> since v11:
> 	document that admin vqs are not counted with regular vqs
> Reviewed-by: Parav Pandit <parav@nvidia.com>
> Reviewed-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>   content.tex | 35 +++++++++++++++++++++++++++++++++++
>   1 file changed, 35 insertions(+)
>
> diff --git a/content.tex b/content.tex
> index 2eb15fa..bcbc06d 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -948,6 +948,10 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>           le64 queue_device;              /* read-write */
>           le16 queue_notify_data;         /* read-only for driver */
>           le16 queue_reset;               /* read-write */
> +
> +        /* About the administration virtqueue. */
> +        le16 admin_queue_index;         /* read-only for driver */
> +        le16 admin_queue_num;         /* read-only for driver */
>   };
>   \end{lstlisting}
>   
> @@ -974,6 +978,7 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>   
>   \item[\field{num_queues}]
>           The device specifies the maximum number of virtqueues supported here.
> +        This excludes administration virtqueues if any are supported.
>   
>   \item[\field{device_status}]
>           The driver writes the device status here (see \ref{sec:Basic Facilities of a Virtio Device / Device Status Field}). Writing 0 into this
> @@ -1033,6 +1038,19 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>           This field exists only if VIRTIO_F_RING_RESET has been
>           negotiated. (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
>   
> +\item[\field{admin_queue_index}]
> +        The device uses this to report the index of the first administration virtqueue.
> +        This field is valid only if VIRTIO_F_ADMIN_VQ has been negotiated.
> +\item[\field{admin_queue_num}]
> +	The device uses this to report the number of the
> +	supported administration virtqueues.
> +	Virtqueues with index
> +	between \field{admin_queue_index} and (\field{admin_queue_index} +
> +	\field{admin_queue_num} - 1) inclusive serve as administration
> +	virtqueues.
> +	The value 0 indicates no supported administration virtqueues.
> +	This field is valid only if VIRTIO_F_ADMIN_VQ has been
> +	negotiated.
>   \end{description}
>   
>   \devicenormative{\paragraph}{Common configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common configuration structure layout}
> @@ -1119,6 +1137,14 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>   were used before the queue reset.
>   (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
>   
> +If VIRTIO_F_ADMIN_VQ has been negotiated, and if the driver
> +configures any administration virtqueues, the driver MUST
> +configure the administration virtqueues using the index
> +in the range \field{admin_queue_index} to
> +\field{admin_queue_index} + \field{admin_queue_num} - 1 inclusive.
> +The driver MAY configure less administration virtqueues than
> +supported by the device.

we need to say something about other virtq's indexes.
For example, if aq index = 0 then for the vblk device the request queues 
would start from index = 1.

can we address this ?

> +
>   \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
>   
>   The notification location is found using the VIRTIO_PCI_CAP_NOTIFY_CFG
> @@ -7686,6 +7712,15 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
>   
>     \item[VIRTIO_F_ADMIN_VQ(41)] This feature indicates that the device exposes one or more
>     administration virtqueues.
> +  At the moment this feature is only supported for devices using
> +  \ref{sec:Virtio Transport Options / Virtio Over PCI
> +	  Bus}~\nameref{sec:Virtio Transport Options / Virtio Over PCI Bus}
> +	  as the transport and is reserved for future use for
> +	  devices using other transports (see
> +	  \ref{drivernormative:Basic Facilities of a Virtio Device / Feature Bits}
> +	and
> +	\ref{devicenormative:Basic Facilities of a Virtio Device / Feature Bits} for
> +	handling features reserved for future use.
>   
>   \end{description}
>