[PATCH v7] virtio-net: Add support for the flexible driver notification structure.

[Vitaly Mireyno <vmireyno@marvell.com>]

Currently, the driver notification (available buffer notification) has a fixed structure, which includes the virtqueue number.
For PCI transport, if notify_off_multiplier > 0, the VQ number can potentially be derived by the device from the Queue Notify address, so providing virtqueue number as part of the data may be redundant.
Some devices benefit from receiving an additional data with driver notifications. This data can optionally replace the vqn field in the driver notification structure.
In its simplest form, it would be sufficient for this data to be a per-device constant value.

Changes from v6:
 * The feature definition is moved to a generic section, referring to PCI-specific details.

Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com>
---
 content.tex | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/content.tex b/content.tex
index b91a132..163c47e 100644
--- a/content.tex
+++ b/content.tex
@@ -965,6 +965,8 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
 struct virtio_pci_notify_cap {
         struct virtio_pci_cap cap;
         le32 notify_off_multiplier; /* Multiplier for queue_notify_off. */
+        le16 notify_data; /* Data to be placed in the vqn field */
+        le16 padding; /* Pad to a dword */
 };
 \end{lstlisting}
 
@@ -984,6 +986,16 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
 the same Queue Notify address for all queues.
 \end{note}
 
+\field{notify_data} is the data that the driver will set in the available
+buffer notification (instead of the virtqueue number), if
+VIRTIO_NET_F_NOTIF_CONFIG_DATA has been negotiated.
+
+\begin{note}
+If \field{notify_off_multiplier} > 0, the virtqueue number can potentially be
+derived by the device from the Queue Notify address, so \field{vqn} may be
+redundant.
+\end{note}
+
 \devicenormative{\paragraph}{Notification capability}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
 The device MUST present at least one notification capability.
 
@@ -1020,6 +1032,9 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
 cap.length >= queue_notify_off * notify_off_multiplier + 4
 \end{lstlisting}
 
+If the device offers VIRTIO_NET_F_NOTIF_CONFIG_DATA, it MUST set
+\field{notify_off_multiplier} > 0 in at least one capability.
+
 \subsubsection{ISR status capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / ISR status capability}
 
 The VIRTIO_PCI_CAP_ISR_CFG capability
@@ -1519,6 +1534,12 @@ \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_NET_F_NOTIF_CONFIG_DATA has been negotiated and
+\field{notify_off_multiplier} > 0, the driver MUST set the 'virtqueue number'
+field of the available buffer notification structure to the \field{notify_data}
+value.
+
 \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:
@@ -2895,6 +2916,10 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
 \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control
     channel.
 
+\item[VIRTIO_NET_F_NOTIF_CONFIG_DATA(57)] Driver provides extra data with
+    available buffer notifications, to aid in notification processing by the
+    device.
+
 \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact \field{hdr_len}
     value. Device benefits from knowing the exact header length.
 
@@ -4180,6 +4205,33 @@ \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device
 See \ref{sec:Basic
 Facilities of a Virtio Device / Virtqueues / Message Framing}.
 
+\subsubsection{Driver Notifications}\label{sec:Device Types / Network Device / Device Operation / Driver 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
+always 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 distinct per-virtqueue address for driver notifications
+(Queue Notify address). In this case, the virtqueue number can potentially be
+derived by the device from the Queue Notify address. For devices, that provide
+per-virtqueue Queue Notify addresses and are able to derive the virtqueue number
+from that address, the virtqueue number in the notification data is redundant.
+On the other hand, some devices can benefit from receiving additional data with
+driver notifications. An example could be a hardware device implementing multiple
+protocols (with virtio being one of them), so the extra notification data could
+serve as a notification type indication or a protocol indication.
+
+VIRTIO_NET_F_NOTIF_CONFIG_DATA feature can be used with transports that support
+a similar driver notifications delivery method, and it allows providing extra
+data by the driver to the device. The definition of the data, that the driver
+provides to the device instead of the virtqueue number, is transport specific.
+
+For more details about driver notifications over PCI see \ref{sec:Virtio
+Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}.
+
+\drivernormative{\paragraph}{Driver Notifications}{Device Types / Network Device / Device Operation / Driver Notifications}
+The driver SHOULD accept the VIRTIO_NET_F_NOTIF_CONFIG_DATA feature if it has
+been offered.
+
 \section{Block Device}\label{sec:Device Types / Block Device}
 
 The virtio block device is a simple virtual block device (ie.
--