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


On 5/15/2022 5:49 PM, Michael S. Tsirkin wrote:

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>
---
  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.

not very clear what is within what.

Simplify the sentence:

The VIRTIO_PCI_CAP_MISC_CFG specifies the location of The miscellaneous
configuration structure.


+Its layout is below.

who's layout? and try to avoid using "below".
better:

The miscellaneous configuration structure has the following layout


+\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 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.
+

set meaning "offered"?


+\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.

"set" is vague. do you mean "negotiated"?

also then let's mandate not negotiating VIRTIO_F_ADMIN_VQ.

also if you are addressing this, address the reverse case
what to do without VIRTIO_F_ADMIN_VQ but with the capability.


is the below good enough ?

"
\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 offered.
The device MUST present a valid \field{admin_queue_index} when VIRTIO_F_ADMIN_VQ is offered.
\drivernormative{\paragraph}{Miscellaneous configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Miscellaneous configuration structure layout} The driver MUST NOT negotiate VIRTIO_F_ADMIN_VQ if VIRTIO_PCI_CAP_MISC_CFG capability is not present.
The driver MAY proceed with other configuration steps in case VIRTIO_F_ADMIN_VQ isn't offered and VIRTIO_PCI_CAP_MISC_CFG is present.
The driver MUST use the value of \field{admin_queue_index} to configure the admin virtqueue, if VIRTIO_F_ADMIN_VQ negotiated and VIRTIO_PCI_CAP_MISC_CFG is present. 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}. 

"






+
+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

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