[VIRTIO GPU PATCH v2 1/1] virtio-gpu: Add new feature flag VIRTIO_GPU_F_FREEZING

[Jiqian Chen <Jiqian.Chen@amd.com>]

When we suspend/resume guest on Xen, the display can't come back.
This is because when guest suspended, it called into Qemu. Then
Qemu destroyed all resources which is used for display. So that
guest's display can't come back to the time when it was suspended.

To solve above problem, I added a new mechanism that when guest is
suspending, it will notify Qemu, and then Qemu will not destroy
resources.

Due to that mechanism needs cooperation between guest and host,
I need to add a new feature flag, so that guest and host can
negotiate whenever freezing is supported or not.

Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
---
 device-types/gpu/description.tex | 35 ++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/device-types/gpu/description.tex b/device-types/gpu/description.tex
index 4435248..729dde5 100644
--- a/device-types/gpu/description.tex
+++ b/device-types/gpu/description.tex
@@ -37,6 +37,8 @@ \subsection{Feature bits}\label{sec:Device Types / GPU Device / Feature bits}
   resources is supported.
 \item[VIRTIO_GPU_F_CONTEXT_INIT (4)] multiple context types and
   synchronization timelines supported.  Requires VIRTIO_GPU_F_VIRGL.
+\item[VIRTIO_GPU_F_FREEZING (5)] freezing virtio-gpu and keeping resources
+  alive is supported.
 \end{description}
 
 \subsection{Device configuration layout}\label{sec:Device Types / GPU Device / Device configuration layout}
@@ -228,6 +230,9 @@ \subsubsection{Device Operation: Request header}\label{sec:Device Types / GPU De
         VIRTIO_GPU_CMD_UPDATE_CURSOR = 0x0300,
         VIRTIO_GPU_CMD_MOVE_CURSOR,
 
+        /* status */
+        VIRTIO_GPU_CMD_STATUS_FREEZING = 0x0400,
+
         /* success responses */
         VIRTIO_GPU_RESP_OK_NODATA = 0x1100,
         VIRTIO_GPU_RESP_OK_DISPLAY_INFO,
@@ -838,6 +843,36 @@ \subsubsection{Device Operation: cursorq}\label{sec:Device Types / GPU Device /
 
 \end{description}
 
+\subsubsection{Device Operation: status}\label{sec:Device Types / GPU Device / Device Operation / Device Operation: cursorq}
+
+\begin{lstlisting}
+struct virtio_gpu_status_freezing {
+  struct virtio_gpu_ctrl_hdr hdr;
+  __u32 freezing;
+};
+\end{lstlisting}
+
+\begin{description}
+
+\item[VIRTIO_GPU_CMD_STATUS_FREEZING]
+Notify freezing status through controlq.
+Request data is \field{struct virtio_gpu_status_freezing}.
+Response type is VIRTIO_GPU_RESP_OK_NODATA.
+
+This is added for S3 function in guest with virtio-gpu. When guest does
+S3, let it notify QEMU if virtio-gpu is in freezing status or not in
+\field{freezing}. Zero means it is not in freezing status, none-zero
+is the opposite. When virtio-gpu is in freezing status, QEMU will not
+destroy resources which are created by using commands
+VIRTIO_GPU_CMD_RESOURCE_CREATE_*, so that guest can use those resources
+to resume display.
+
+Note: this change is not enough to solve the problems of S4 function.
+QEMU may lose resources after hibernation. It needs more research and
+development.
+
+\end{description}
+
 \subsection{VGA Compatibility}\label{sec:Device Types / GPU Device / VGA Compatibility}
 
 Applies to Virtio Over PCI only.  The GPU device can come with and
-- 
2.34.1