[virtio-comment] [PATCH v9] virtio-net: Add support for the flexible driver notification structure.

* [virtio-comment] [PATCH v9] virtio-net: Add support for the flexible driver notification structure.
@ 2020-11-05 22:41 Vitaly Mireyno
  2020-11-19 15:57 ` [virtio-comment] " Vitaly Mireyno
  2020-11-23 16:16 ` [virtio-comment] " Halil Pasic
  0 siblings, 2 replies; 8+ messages in thread
From: Vitaly Mireyno @ 2020-11-05 22:41 UTC (permalink / raw)
  To: virtio-comment; +Cc: Michael S. Tsirkin, Jason Wang, Ariel Elior

When the driver is required to send an available buffer notification to the device, it sends the virtqueue number to be notified.
With this new feature, the device can optionally provide a per-virtqueue value for the driver to use in driver notifications, instead of the virtqueue number.
Some devices may benefit from this flexibility by providing, for example, an internal virtqueue identifier, or an internal offset related to the virtqueue number.

Changes from v8:
 * Incorporated comments for v8:
     - moved the feature from a network device to a global section
     - few minor changes

Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com>
---
 content.tex | 46 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/content.tex b/content.tex
index 91735e3..bf50bfd 100644
--- a/content.tex
+++ b/content.tex
@@ -824,6 +824,7 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
         le64 queue_desc;                /* read-write */
         le64 queue_driver;              /* read-write */
         le64 queue_device;              /* read-write */
+        le16 queue_notify_data;         /* read-only for driver */
 };
 \end{lstlisting}
 
@@ -890,6 +891,19 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
 
 \item[\field{queue_device}]
         The driver writes the physical address of Device Area here.  See section \ref{sec:Basic Facilities of a Virtio Device / Virtqueues}.
+
+\item[\field{queue_notify_data}]
+        This field exists only if VIRTIO_F_NOTIF_CONFIG_DATA has been negotiated.
+        The driver will use this value to put it in the 'virtqueue number' field
+        in the available buffer notification structure.
+        See section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Available Buffer Notifications}.
+        \begin{note}
+        This field provides the device with flexibility to determine how virtqueues
+        will be referred to in available buffer notifications.
+        In a trivial case the device can set \field{queue_notify_data}=vqn. Some devices
+        may benefit from providing another value, for example an internal virtqueue
+        identifier, or an internal offset related to the virtqueue number.
+        \end{note}
 \end{description}
 
 \devicenormative{\paragraph}{Common configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common configuration structure layout}
@@ -940,7 +954,7 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
 
 \drivernormative{\paragraph}{Common configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common configuration structure layout}
 
-The driver MUST NOT write to \field{device_feature}, \field{num_queues}, \field{config_generation} or \field{queue_notify_off}.
+The driver MUST NOT write to \field{device_feature}, \field{num_queues}, \field{config_generation}, \field{queue_notify_off} or \field{queue_notify_data}.
 
 If VIRTIO_F_RING_PACKED has been negotiated,
 the driver MUST NOT write the value 0 to \field{queue_size}.
@@ -1519,6 +1533,15 @@ \subsubsection{Available Buffer Notifications}\label{sec:Virtio Transport Option
 See \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
 for how to calculate the Queue Notify address.
 
+\drivernormative{\paragraph}{Available Buffer Notifications}{Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Available Buffer Notifications}
+If VIRTIO_F_NOTIF_CONFIG_DATA has been negotiated:
+\begin{itemize}
+\item If VIRTIO_F_NOTIFICATION_DATA has not been negotiated, the driver MUST use the
+\field{queue_notify_data} value instead of the virtqueue index.
+\item If VIRTIO_F_NOTIFICATION_DATA has been negotiated, the driver MUST set the
+\field{vqn} field to the \field{queue_notify_data} value.
+\end{itemize}
+
 \subsubsection{Used Buffer Notifications}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Used Buffer Notifications}
 
 If a used buffer notification is necessary for a virtqueue, the device would typically act as follows:
@@ -6132,6 +6155,25 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
   that the driver passes extra data (besides identifying the virtqueue)
   in its device notifications.
   See \ref{sec:Virtqueues / Driver notifications}~\nameref{sec:Virtqueues / Driver notifications}.
+
+  \item[VIRTIO_F_NOTIF_CONFIG_DATA(39)] This feature indicates that the driver
+  uses the data provided by the device as a virtqueue identifier in available
+  buffer notifications.
+  As mentioned in section \ref{sec:Virtqueues / Driver notifications}, when the
+  driver is required to send an available buffer notification to the device, it
+  sends the virtqueue number to be notified. The method of delivering
+  notifications is transport specific.
+  With the PCI transport, the device can optionally provide a per-virtqueue value
+  for the driver to use in driver notifications, instead of the virtqueue number.
+  Some devices may benefit from this flexibility by providing, for example,
+  an internal virtqueue identifier, or an internal offset related to the
+  virtqueue number.
+
+  This feature indicates the availability of such value. The definition of the
+  data to be provided in driver notification and the delivery method is
+  transport specific.
+  For more details about driver notifications over PCI see \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Available Buffer Notifications}.
+
 \end{description}
 
 \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
@@ -6166,6 +6208,8 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
 or partially reset, and even without re-negotiating
 VIRTIO_F_SR_IOV after the reset.
 
+A driver SHOULD accept VIRTIO_F_NOTIF_CONFIG_DATA if it is offered.
+
 \devicenormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
 
 A device MUST offer VIRTIO_F_VERSION_1.  A device MAY fail to operate further
--

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