[PATCH V7 v7] virtio: introduce SUSPEND bit in device status

[Zhu Lingshan <lingshan.zhu@amd.com>]

This commit allows the driver to suspend the device by
introducing a new status bit SUSPEND in device_status.

This commit also introduce a new feature bit VIRTIO_F_SUSPEND
which indicating whether the device support SUSPEND.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Zhu Lingshan <lingshan.zhu@amd.com>
Signed-off-by: David Stevens <stevensd@chromium.org>
---
 content.tex | 75 ++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 65 insertions(+), 10 deletions(-)

Changes from V6:
- the device should hold its config interrupt while SUSPEND,
 and send config interrupt when the SUSPEND bit is cleared.
- while SUSPEND, the driver MUST NOT access Device Configuration Space
- minor changes.

Changes from V5:
- the device should present NEEDS_RESET if failed to suspend
- allow the driver access device status in the config space when
  suspended if it is implemented in config space.
- language improvements

Changes from V4:
- re-order the device status bits section
- kick vqs --> notify vqs

Changes from V3:
- allow the driver clearing the SUSPEND bit to resume the device.
- disallow access to config space while suspended.

diff --git a/content.tex b/content.tex
index 0a62dce..2d1bee8 100644
--- a/content.tex
+++ b/content.tex
@@ -36,19 +36,22 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
     this bit.  For example, under Linux, drivers can be loadable modules.
   \end{note}
 
-\item[FAILED (128)] Indicates that something went wrong in the guest,
-  and it has given up on the device. This could be an internal
-  error, or the driver didn't like the device for some reason, or
-  even a fatal error during device operation.
+\item[DRIVER_OK (4)] Indicates that the driver is set up and ready to
+  drive the device.
 
 \item[FEATURES_OK (8)] Indicates that the driver has acknowledged all the
   features it understands, and feature negotiation is complete.
 
-\item[DRIVER_OK (4)] Indicates that the driver is set up and ready to
-  drive the device.
+\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.
+
+\item[FAILED (128)] Indicates that something went wrong in the guest,
+  and it has given up on the device. This could be an internal
+  error, or the driver didn't like the device for some reason, or
+  even a fatal error during device operation.
 \end{description}
 
 The \field{device status} field starts out as 0, and is reinitialized to 0 by
@@ -60,8 +63,9 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
 initialization sequence specified in
 \ref{sec:General Initialization And Device Operation / Device
 Initialization}.
-The driver MUST NOT clear a
-\field{device status} bit.  If the driver sets the FAILED bit,
+The driver MUST NOT clear a \field{device status} bit other than SUSPEND
+except when setting \field{device status} to 0 as a transport-specific way to
+initiate a reset. If the driver sets the FAILED bit,
 the driver MUST later reset the device before attempting to re-initialize.
 
 The driver SHOULD NOT rely on completion of operations of a
@@ -99,10 +103,10 @@ \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature B
 \begin{description}
 \item[0 to 23, and 50 to 127] Feature bits for the specific device type
 
-\item[24 to 41] Feature bits reserved for extensions to the queue and
+\item[24 to 42] Feature bits reserved for extensions to the queue and
   feature negotiation mechanisms
 
-\item[42 to 49, and 128 and above] Feature bits reserved for future extensions.
+\item[43 to 49, and 128 and above] Feature bits reserved for future extensions.
 \end{description}
 
 \begin{note}
@@ -629,6 +633,53 @@ \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}
+
+When VIRTIO_F_SUSPEND is negotiated, the driver can set the
+SUSPEND bit in \field{device status} to suspend a device, and can
+clear the SUSPEND bit to resume a suspended device.
+
+\drivernormative{\subsection}{Device Suspend}{General Initialization And Device Operation / Device Suspend}
+
+The driver MUST NOT set SUSPEND if FEATURES_OK is not set or VIRTIO_F_SUSPEND is not negotiated.
+
+Once the driver sets SUSPEND to \field{device status} of the device:
+\begin{itemize}
+\item The driver MUST re-read \field{device status} to verify whether the SUSPEND bit is set.
+\item The driver MUST NOT make any more buffers available to the device.
+\item The driver MUST NOT access any virtqueues or send notifications for any virtqueues.
+\item The driver MUST NOT access Device Configuration Space.
+\end{itemize}
+
+\devicenormative{\subsection}{Device Suspend}{General Initialization And Device Operation / Device Suspend}
+
+The device MUST ignore SUSPEND if FEATURES_OK is not set or VIRTIO_F_SUSPEND is not negotiated.
+
+The device MUST ignore all 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 virtqeuues,
+access any virtqueues, or modify any fields in
+its Configuration Space while suspended.
+
+If changes occur in the Configuration Space while the SUSPEND bit is set,
+the device MUST NOT send any configuration change notifications.
+Instead, the device MUST send the notification after the SUSPEND bit has been cleared.
+
+When the driver sets SUSPEND, the device MUST either suspend itself or set DEVICE_NEEDS_RESET if failed to suspend.
+
+If SUSPEND is set in \field{device status}, when the driver clears SUSPEND,
+the device MUST either resume normal operation or set DEVICE_NEEDS_RESET.
+
+When the driver sets SUSPEND,
+the device SHOULD perform the following actions before presenting that the SUSPEND bit is set to 1 in the \field{device status}:
+
+\begin{itemize}
+\item Stop processing 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(42)] This feature indicates that the driver can
+   trigger suspending the device via the SUSPEND flag
+   See \ref{sec:Basic Facilities of a Virtio Device / Device Status Field}.
+
 \end{description}
 
 \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
-- 
2.45.2