[PATCH 00/12] misc/syncobj: add /dev/syncobj device

[Julian Orth]

This series adds a new device /dev/syncobj that can be used to create
and manipulate DRM syncobjs. Previously, these operations required the
use of a DRM device and the device needed to support the DRIVER_SYNCOBJ
and DRIVER_SYNCOBJ_TIMELINE features.

There are several issues with the existing API:

- Syncobjs are the only explicit sync mechanism available on wayland.
  Most compositors do not use GPU waits. Instead, they use the
  DRM_IOCTL_SYNCOBJ_EVENTFD ioctl to perform a CPU wait. Being tied to
  DRM devices means that compositors cannot consistently offer this
  feature even though no device-specific logic is involved.
- llvmpipe currently cannot offer syncobj interop because it does not
  have access to a DRM device. This means that applications using
  llvmpipe cannot present images before they have finished rendering,
  despite llvmpipe using threaded rendering.
- Clients that do not use the Vulkan WSI need to manually probe /dev/dri
  for devices that support the syncobj ioctls in order to use the
  wayland syncobj protocol.
- Similarly, clients that want to use screen capture have no equivalent
  to the WSI and are therefore forced into that path.
- Having to keep a DRM device open has potentially negative interactions
  with GPU hotplug.
- Having to translate between syncobj FDs and handles is troublesome in
  the compositor usecase since syncobjs come and go frequently and need
  to be cleaned up when clients disconnect.

/dev/syncobj solves these issues by providing all syncobj ioctls under a
consistent path that is not tied to any DRM device. It also operates
directly on file descriptors instead of syncobj handles.

The series starts with a number of small refactorings in drm_syncobj.c
to make its functionality available outside of the file and without the
need for drm_file/handle pairs.

The last commit adds the /dev/syncobj module. I've added it as a misc
device but maybe this should instead live somewhere under gpu/drm.

An application using the new interface can be found at [1].

[1]: https://github.com/mahkoh/jay/pull/947

---
Julian Orth (12):
      drm/syncobj: add drm_syncobj_from_fd
      drm/syncobj: add drm_syncobj_fence_lookup
      drm/syncobj: make drm_syncobj_array_wait_timeout public
      drm/syncobj: add drm_syncobj_register_eventfd
      drm/syncobj: have transfer functions accept drm_syncobj directly
      drm/syncobj: add drm_syncobj_transfer
      drm/syncobj: add drm_syncobj_timeline_signal
      drm/syncobj: add drm_syncobj_query
      drm/syncobj: fix resource leak in drm_syncobj_import_sync_file_fence
      drm/syncobj: add drm_syncobj_import_sync_file
      drm/syncobj: add drm_syncobj_export_sync_file
      misc/syncobj: add new device

 Documentation/userspace-api/ioctl/ioctl-number.rst |   1 +
 drivers/gpu/drm/drm_syncobj.c                      | 374 ++++++++++++++-----
 drivers/misc/Kconfig                               |  10 +
 drivers/misc/Makefile                              |   1 +
 drivers/misc/syncobj.c                             | 404 +++++++++++++++++++++
 include/drm/drm_syncobj.h                          |  21 ++
 include/uapi/linux/syncobj.h                       |  75 ++++
 7 files changed, 795 insertions(+), 91 deletions(-)
---
base-commit: 6916d5703ddf9a38f1f6c2cc793381a24ee914c6
change-id: 20260516-jorth-syncobj-d4d374c8c61b

Best regards,
--  
Julian Orth <ju.orth@xxxxxxxxx>