[VIRTIO PCI PATCH v5 1/1] transport-pci: Add freeze_mode to virtio_pci_common_cfg

[Jiqian Chen]

When guest vm does S3, Qemu will reset and clear some things of virtio
devices, but guest can't aware that, so that may cause some problems.
For excample, Qemu calls virtio_reset->virtio_gpu_gl_reset when guest
resume, that function will destroy render resources of virtio-gpu. As
a result, after guest resume, the display can't come back and we only
saw a black screen. Due to guest can't re-create all the resources, so
we need to let Qemu not to destroy them when S3.

For above purpose, we need a mechanism that allows guests and QEMU to
negotiate their reset behavior. So this patch add a new parameter
named freeze_mode to struct virtio_pci_common_cfg. And when guest
suspends, it can write freeze_mode to be FREEZE_S3, and then virtio
devices can change their reset behavior on Qemu side according to
freeze_mode. What's more, freeze_mode can be used for all virtio
devices to affect the behavior of Qemu, not just virtio gpu device.

Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
---
 transport-pci.tex | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/transport-pci.tex b/transport-pci.tex
index a5c6719..2543536 100644
--- a/transport-pci.tex
+++ b/transport-pci.tex
@@ -319,6 +319,7 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
         le64 queue_desc;                /* read-write */
         le64 queue_driver;              /* read-write */
         le64 queue_device;              /* read-write */
+        le16 freeze_mode;               /* read-write */
         le16 queue_notif_config_data;   /* read-only for driver */
         le16 queue_reset;               /* read-write */
 
@@ -393,6 +394,12 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
 \item[\field{queue_device}]
         The driver writes the physical address of Device Area here.  See section \ref{sec:Basic Facilities of a Virtio Device / Virtqueues}.
 
+\item[\field{freeze_mode}]
+        The driver writes this to set the freeze mode of virtio pci.
+        VIRTIO_PCI_FREEZE_MODE_UNFREEZE - virtio-pci is running;
+        VIRTIO_PCI_FREEZE_MODE_FREEZE_S3 - guest vm is doing S3, and virtio-pci enters S3 suspension;
+        Other values are reserved for future use, like S4, etc.
+
 \item[\field{queue_notif_config_data}]
         This field exists only if VIRTIO_F_NOTIF_CONFIG_DATA has been negotiated.
         The driver will use this value when driver sends available buffer
-- 
2.34.1