[PATCH v9 0/3] Virtio-GPU S4 support

[dongwon.kim@intel.com]

From: Dongwon Kim <dongwon.kim@intel.com>

This patch series implements the .freeze and .restore hooks for the virtio-gpu
driver, alongside a PM notifier to properly handle object tracking and 
restoration for S4 (hibernation) scenarios.

The first patch adds the `virtgpu_freeze` and `virtgpu_restore` functions. 
These functions orchestrate flushing pending work, safely deleting virtio 
queues before suspension once they are empty, and recreating them during 
the restoration process.

The second patch implements a tracking and recreation mechanism for active 
`virtio_gpu_object` instances. This is necessary because the host hypervisor 
(e.g., QEMU) terminates or resets the backend during a full hibernation cycle, 
wiping out all previously established graphics resources and causing post-resume 
errors in the guest.

The third patch integrates a PM notifier block into the driver. It captures 
the PM_HIBERNATION_PREPARE phase to check compatibility (blocking S4 if Virgl 
3D is active) and sets a state flag. This flag instructs `virtgpu_restore` to 
fully re-submit and restore active GPU objects immediately after the fresh 
virtqueues are reconfigured.

These changes ensure that the virtio-gpu driver can cleanly survive guest 
hibernation without experiencing host-side resource loss.

v2: 10ms sleep is added in virtgpu_freeze to avoid the situation
    the driver is locked up during resumption.

v3: Plain 10ms delay (v2) is replaced with wait calls which wait until
    the virtio queue is empty.
    (Dmitry Osipenko)

v4: New version of patchset only covers S4 case because loss of resources in S3
    case can be avoided by skipping virtio-gpu-reset in QEMU (hw/display/virtio-gpu.c).
    To skip virtio-gpu-reset (soft-reset), virtio-gpu-pci device should be attached to
    PCIE bus AND a PCIE option, 'x-pcie-pm-no-soft-reset' should added and set to 'true'.
    (e.g. -device virtio-gpu-pci,bus=port,x-pcie-pm-no-soft-reset=true)

v5: Remove virtio_gpu_object from the restore list before freeing the object
    to prevent an use-after-free situation.
    (Nirmoy Das)

    Protect restore list operations with a spinlock
    (Nirmoy Das)

    Move restore list node into virtio_gpu_bo struct to reduce memory usage
    (Dmitry Osipenko)

    Remove unused header - drm_atomic_helper.h
    (Dmitry Osipenko)

v6: Include object backed by imported dmabuf
    (Dmitry Osipenko)

    Not storing virgl objects in the restore_list as virgl 3D objects are not
    recoverable.
    (Dmitry Osipenko)

    Change the name 'list',a node in restore_list to 'restore_node'
    (Nirmoy Das)

    Use mutex instead of spinlock when updating restore_list
    (Nirmoy Das)

    Initialize restore_node when virtio_gpu_object is created - this is to
    check if the node is in the list with 'list_empty' before removing it.

    Restoring objects in the PM notifier is too late, as virtio-gpu
    message communication begins in virtgpu_restore once virtqueues
    are re-established. To address this, a 'hibernation' flag is set
    during the PM_HIBERNATION_PREPARE phase in the notifier. This flag
    is then used in virtgpu_restore to detect if the system is resuming
    from S4, allowing objects to be recovered immediately after virtqueues
    are reconfigured.

v7: Add a helper, virtio_gpu_add_object_to_restore_list
    (Dmitry Osipenko)

    Unreference all objects before hibernation so they can be removed
    on the host side, since they will be fully restored anyway. This
    prevents the situation where host-side hibernation fails (leaving
    all associated resources still alive) while the virtio-gpu driver
    still attempts to restore those objects.
    (Dmitry Osipenko)

v8: Add drm_print.h to virtgpu_prime.c

v9: Move duplicate wait_event_timeout blocks into a single
    virtio_gpu_wait_queue helper function.
    (Dmitry Osipenko)

    Handle timeouts gracefully by returning -ETIMEDOUT to abort
    the freeze operation if the host hangs.
    (Dmitry Osipenko)

Dongwon Kim (3):
  drm/virtio: Freeze and restore hooks to support suspend and resume
  drm/virtio: Add support for saving and restoring virtio_gpu_objects
  drm/virtio: Add PM notifier to restore objects after hibernation

 drivers/gpu/drm/virtio/virtgpu_drv.c    | 80 ++++++++++++++++++++++-
 drivers/gpu/drm/virtio/virtgpu_drv.h    | 25 ++++++-
 drivers/gpu/drm/virtio/virtgpu_kms.c    | 54 +++++++++++++--
 drivers/gpu/drm/virtio/virtgpu_object.c | 87 ++++++++++++++++++++++++-
 drivers/gpu/drm/virtio/virtgpu_prime.c  | 45 ++++++++++++-
 drivers/gpu/drm/virtio/virtgpu_vq.c     | 30 ++++++++-
 drivers/gpu/drm/virtio/virtgpu_vram.c   |  5 +-
 7 files changed, 312 insertions(+), 14 deletions(-)

-- 
2.34.1