[PATCH v4 3/3] virtio: introduce SUSPEND and RESUME feature

This commit allows the driver to suspend the
device through a new device status bit SUSPEND
and resume the device running by re-setting
DRIVER_OK bit in device status.

Signed-off-by: Zhu Lingshan <[email protected]>
Signed-off-by: Jason Wang <[email protected]>
Fixes: https://github.com/oasis-tcs/virtio-spec/issues/229
---
 content.tex | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 57 insertions(+), 2 deletions(-)

diff --git a/content.tex b/content.tex
index 9213dc0..32cabfa 100644
--- a/content.tex
+++ b/content.tex
@@ -42,6 +42,9 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
 \item[FEATURES_OK (8)] Indicates that the driver has acknowledged all the
   features it understands, and feature negotiation is complete.
 
+\item[SUSPEND (16)] When VIRTIO_F_SUSPEND is negotiated, indicates that the
+  device has been suspended by the driver.
+
 \item[DEVICE_NEEDS_RESET (64)] Indicates that the device has experienced
   an error from which it can't recover.
 
@@ -99,10 +102,10 @@ \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature B
 \begin{description}
 \item[0 to 23, 41, 42 and 50 to 127] Feature bits for the specific device type
 
-\item[24 to 40] Feature bits reserved for extensions to the queue and
+\item[24 to 40, and 43] Feature bits reserved for extensions to the queue and
   feature negotiation mechanisms, see \ref{sec:Reserved Feature Bits}
 
-\item[43 to 49, and 128 and above] Feature bits reserved for future extensions.
+\item[44 to 49, and 128 and above] Feature bits reserved for future extensions.
 \end{description}
 
 \begin{note}
@@ -629,6 +632,54 @@ \section{Device Cleanup}\label{sec:General Initialization And Device Operation /
 
 Thus a driver MUST ensure a virtqueue isn't live (by device reset) before removing exposed buffers.
 
+\section{Device Suspend}\label{sec:General Initialization And Device Operation / Device Suspend}
+
+If VIRTIO_F_SUSPEND is negotiated, the driver is eligible to suspend the device by setting the SUSPEND bit in \field{device status} to 1, and the device sets the DRIVER_OK bit to 0 once it has been suspended.
+
+If the device has been suspended, the driver can resume the device running by setting the DRIVER_OK bit in \field{device status} to 1, and the device sets the SUSPEND bit to 0 once it resumes running.
+
+\drivernormative{\subsection}{Device Suspend}{General Initialization And Device Operation / Device Suspend}
+
+The driver SHOULD NOT set SUSPEND bit if DRIVER_OK is not set or VIRTIO_F_SUSPEND is not negotiated.
+
+Once the driver sets SUSPEND bit in \field{device status} to 1:
+\begin{itemize}
+\item The driver MUST verify whether the device has been suspended by re-reading \field{device status}, examining whether the SUSPEND bit is set to 1 and the DRIVER_OK bit is set to 0.
+\item The driver MUST NOT make any more buffers available to the device.
+\item The driver MUST NOT send notifications for any virtqueues.
+\item The driver MUST NOT make any changes to Device Configuration Space except for \field{device status} if it is part of the Configuration Space.
+\end{itemize}
+
+\devicenormative{\subsection}{Device Suspend}{General Initialization And Device Operation / Device Suspend}
+
+The device MUST ignore any operations on the SUSPEND bit from the driver if the device has not been completely initialized by the procedures in \ref{sec:General Initialization And Device Operation / Device Initialization}
+
+The device SHOULD ignore any write access to its Configuration Space while
+suspended, except for \field{device status} if it is part of the Configuration Space.
+
+A device MUST NOT send any notifications for any virtqueues,
+access any virtqueues, or modify any fields in
+its Configuration Space while suspended.
+
+If changes occur in the Configuration Space during suspended period,
+the device MUST NOT send any configuration change notifications.
+Instead, the device MUST send the notification when it resumes running.
+
+If the driver sets the SUSPEND bit in \field{device status} to 1,
+the device MUST either suspend itself or set the DEVICE_NEEDS_RESET bit in \field{device status} to 1 when it fails to suspend.
+
+If the device has been suspended and the driver resumes the device running by setting the DRIVER_OK bit in \field{device status} to 1,
+the device MUST either resume normal operation or set the DEVICE_NEEDS_RESET bit in \field{device status} to 1 when it fails to resume.
+
+When the driver sets the SUSPEND bit to 1,
+the device SHOULD perform the following actions before presenting the SUSPEND bit as 1 and DRIVER_OK bit as 0 in the \field{device status}:
+
+\begin{itemize}
+\item Stop consuming more buffers of any virtqueues.
+\item Wait until all buffers that are being processed have been used.
+\item Send used buffer notifications to the driver.
+\end{itemize}
+
 \chapter{Virtio Transport Options}\label{sec:Virtio Transport Options}
 
 Virtio can use various different buses, thus the standard is split
@@ -872,6 +923,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
 	\ref{devicenormative:Basic Facilities of a Virtio Device / Feature Bits} for
 	handling features reserved for future use.
 
+  \item[VIRTIO_F_SUSPEND(43)] This feature indicates that the driver can
+   suspend the device by set the SUSPEND bit to 1.
+   See \ref{sec:Basic Facilities of a Virtio Device / Device Status Field}.
+
 \end{description}
 
 \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
-- 
2.49.0