content: document speed, duplex

Document as used by Linux.

Fixes: https://github.com/oasis-tcs/virtio-spec/issues/59
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>

1 files changed, 37 insertions, 1 deletions

diff --git a/content.tex b/content.tex
index 307e66f..b91a132 100644
--- a/content.tex
+++ b/content.tex
@@ -2907,6 +2907,8 @@ features.
 
 \item[VIRTIO_NET_F_STANDBY(62)] Device may act as a standby for a primary
     device with the same MAC address.
+
+\item[VIRTIO_NET_F_SPEED_DUPLEX(63)] Device reports speed and duplex.
 \end{description}
 
 \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device / Feature bits / Feature bit requirements}
@@ -2967,7 +2969,19 @@ The following driver-read-only field, \field{mtu} only exists if
 VIRTIO_NET_F_MTU is set. This field specifies the maximum MTU for the driver to
 use.
 
-Two following fields, \field{speed} and \field{duplex} are reserved.
+The following two fields, \field{speed} and \field{duplex}, only
+exist if VIRTIO_NET_F_SPEED_DUPLEX is set.
+
+\field{speed} contains the device speed, in units of 1 MBit per
+second, 0 to 0x7ffffffff, or 0xfffffffff for unknown speed.
+
+\field{duplex} has the values of 0x00 for full duplex, 0x01 for
+half duplex and 0xff for unknown duplex state.
+
+Both \field{speed} and \field{duplex} can change, thus the driver
+is expected to re-read these values after receiving a
+configuration change notification.
+
 \begin{lstlisting}
 struct virtio_net_config {
         u8 mac[6];
@@ -3042,6 +3056,19 @@ VIRTIO_NET_F_RSS.
 If the driver negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act
 as a standby device for a primary device with the same MAC address.
 
+If VIRTIO_NET_F_SPEED_DUPLEX has been negotiated, \field{speed}
+MUST contain the device speed, in units of 1 MBit per second, 0 to
+0x7ffffffff, or 0xfffffffff for unknown.
+
+If VIRTIO_NET_F_SPEED_DUPLEX has been negotiated, \field{duplex}
+MUST have the values of 0x00 for full duplex, 0x01 for half
+duplex, or 0xff for unknown.
+
+If VIRTIO_NET_F_SPEED_DUPLEX and VIRTIO_NET_F_STATUS have both
+been negotiated, the device SHOULD NOT change the \field{speed} and
+\field{duplex} fields as long as VIRTIO_NET_S_LINK_UP is set in
+the \field{status}.
+
 \drivernormative{\subsubsection}{Device configuration layout}{Device Types / Network Device / Device configuration layout}
 
 A driver SHOULD negotiate VIRTIO_NET_F_MAC if the device offers it.
@@ -3066,6 +3093,15 @@ with \field{gso_type} NONE or ECN.
 
 A driver SHOULD negotiate the VIRTIO_NET_F_STANDBY feature if the device offers it.
 
+If VIRTIO_NET_F_SPEED_DUPLEX has been negotiated,
+the driver MUST treat any value of \field{speed} above
+0x7fffffff as well as any value of \field{duplex} not
+matching 0x00 or 0x01 as an unknown value.
+
+If VIRTIO_NET_F_SPEED_DUPLEX has been negotiated, the driver
+SHOULD re-read \field{speed} and \field{duplex} after a
+configuration change notification.
+
 \subsubsection{Legacy Interface: Device configuration layout}\label{sec:Device Types / Network Device / Device configuration layout / Legacy Interface: Device configuration layout}
 \label{sec:Device Types / Block Device / Feature bits / Device configuration layout / Legacy Interface: Device configuration layout}
 When using the legacy interface, transitional devices and drivers