Re: [PATCH v1 5/5] Add miscellaneous configuration structure for PCI

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 4/4/2022 4:04 PM, Michael S. Tsirkin wrote:
> On Wed, Mar 02, 2022 at 05:56:08PM +0200, 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>
>> ---
>>   conformance.tex |  2 ++
>>   content.tex     | 25 +++++++++++++++++++++++++
>>   2 files changed, 27 insertions(+)
>>
>> diff --git a/conformance.tex b/conformance.tex
>> index 129831c..e31645e 100644
>> --- a/conformance.tex
>> +++ b/conformance.tex
>> @@ -102,6 +102,7 @@ \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}
>> @@ -363,6 +364,7 @@ \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..bf46192 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 +1355,28 @@ \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.
>> +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}
>> +
>> +\devicenormative{\paragraph}{Miscellaneous configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Miscellaneous configuration structure layout}
>> +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 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
> This is useful, but I think we'll want this for all transports then.

I think that adding more transports can be incremental and should be a 
no-go for merging this patch set.

We discussed this in the previous version and nobody had a conclusion on 
the right approach for other transports.

>
>
>> -- 
>> 2.21.0