src/protocol/linux-drm-syncobj-v1.xml

<?xml version="1.0" encoding="UTF-8"?>
<protocol name="linux_drm_syncobj_v1">
  <copyright>
    Copyright 2016 The Chromium Authors.
    Copyright 2017 Intel Corporation
    Copyright 2018 Collabora, Ltd
    Copyright 2021 Simon Ser

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
    to deal in the Software without restriction, including without limitation
    the rights to use, copy, modify, merge, publish, distribute, sublicense,
    and/or sell copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice (including the next
    paragraph) shall be included in all copies or substantial portions of the
    Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.
  </copyright>

  <description summary="protocol for providing explicit synchronization">
    This protocol allows clients to request explicit synchronization for
    buffers. It is tied to the Linux DRM synchronization object framework.

    Synchronization refers to co-ordination of pipelined operations performed
    on buffers. Most GPU clients will schedule an asynchronous operation to
    render to the buffer, then immediately send the buffer to the compositor
    to be attached to a surface.

    With implicit synchronization, ensuring that the rendering operation is
    complete before the compositor displays the buffer is an implementation
    detail handled by either the kernel or userspace graphics driver.

    By contrast, with explicit synchronization, DRM synchronization object
    timeline points mark when the asynchronous operations are complete. When
    submitting a buffer, the client provides a timeline point which will be
    waited on before the compositor accesses the buffer, and another timeline
    point that the compositor will signal when it no longer needs to access the
    buffer contents for the purposes of the surface commit.

    Linux DRM synchronization objects are documented at:
    https://dri.freedesktop.org/docs/drm/gpu/drm-mm.html#drm-sync-objects

    Warning! The protocol described in this file is currently in the testing
    phase. Backward compatible changes may be added together with the
    corresponding interface version bump. Backward incompatible changes can
    only be done by creating a new major version of the extension.
  </description>

  <interface name="wp_linux_drm_syncobj_manager_v1" version="1">
    <description summary="global for providing explicit synchronization">
      This global is a factory interface, allowing clients to request
      explicit synchronization for buffers on a per-surface basis.

      See wp_linux_drm_syncobj_surface_v1 for more information.
    </description>

    <request name="destroy" type="destructor">
      <description summary="destroy explicit synchronization factory object">
        Destroy this explicit synchronization factory object. Other objects
        shall not be affected by this request.
      </description>
    </request>

    <enum name="error">
      <entry name="surface_exists" value="0"
        summary="the surface already has a synchronization object associated"/>
      <entry name="invalid_timeline" value="1"
        summary="the timeline object could not be imported"/>
    </enum>

    <request name="get_surface">
      <description summary="extend surface interface for explicit synchronization">
        Instantiate an interface extension for the given wl_surface to provide
        explicit synchronization.

        If the given wl_surface already has an explicit synchronization object
        associated, the surface_exists protocol error is raised.

        Graphics APIs, like EGL or Vulkan, that manage the buffer queue and
        commits of a wl_surface themselves, are likely to be using this
        extension internally. If a client is using such an API for a
        wl_surface, it should not directly use this extension on that surface,
        to avoid raising a surface_exists protocol error.
      </description>
      <arg name="id" type="new_id" interface="wp_linux_drm_syncobj_surface_v1"
        summary="the new synchronization surface object id"/>
      <arg name="surface" type="object" interface="wl_surface"
        summary="the surface"/>
    </request>

    <request name="import_timeline">
      <description summary="import a DRM syncobj timeline">
        Import a DRM synchronization object timeline.

        If the FD cannot be imported, the invalid_timeline error is raised.
      </description>
      <arg name="id" type="new_id" interface="wp_linux_drm_syncobj_timeline_v1"/>
      <arg name="fd" type="fd" summary="drm_syncobj file descriptor"/>
    </request>
  </interface>

  <interface name="wp_linux_drm_syncobj_timeline_v1" version="1">
    <description summary="synchronization object timeline">
      This object represents an explicit synchronization object timeline
      imported by the client to the compositor.
    </description>

    <request name="destroy" type="destructor">
      <description summary="destroy the timeline">
        Destroy the synchronization object timeline. Other objects are not
        affected by this request, in particular timeline points set by
        set_acquire_point and set_release_point are not unset.
      </description>
    </request>
  </interface>

  <interface name="wp_linux_drm_syncobj_surface_v1" version="1">
    <description summary="per-surface explicit synchronization">
      This object is an add-on interface for wl_surface to enable explicit
      synchronization.

      Each surface can be associated with only one object of this interface at
      any time.

      Explicit synchronization is guaranteed to be supported for buffers
      created with any version of the linux-dmabuf protocol. Compositors are
      free to support explicit synchronization for additional buffer types.
      If at surface commit time the attached buffer does not support explicit
      synchronization, an unsupported_buffer error is raised.

      As long as the wp_linux_drm_syncobj_surface_v1 object is alive, the
      compositor may ignore implicit synchronization for buffers attached and
      committed to the wl_surface. The delivery of wl_buffer.release events
      for buffers attached to the surface becomes undefined.

      Clients must set both acquire and release points if and only if a
      non-null buffer is attached in the same surface commit. See the
      no_buffer, no_acquire_point and no_release_point protocol errors.

      If at surface commit time the acquire and release DRM syncobj timelines
      are identical, the acquire point value must be strictly less than the
      release point value, or else the conflicting_points protocol error is
      raised.
    </description>

    <request name="destroy" type="destructor">
      <description summary="destroy the surface synchronization object">
        Destroy this surface synchronization object.

        Any timeline point set by this object with set_acquire_point or
        set_release_point since the last commit may be discarded by the
        compositor. Any timeline point set by this object before the last
        commit will not be affected.
      </description>
    </request>

    <enum name="error">
      <entry name="no_surface" value="1"
        summary="the associated wl_surface was destroyed"/>
      <entry name="unsupported_buffer" value="2"
        summary="the buffer does not support explicit synchronization"/>
      <entry name="no_buffer" value="3" summary="no buffer was attached"/>
      <entry name="no_acquire_point" value="4"
        summary="no acquire timeline point was set"/>
      <entry name="no_release_point" value="5"
        summary="no release timeline point was set"/>
      <entry name="conflicting_points" value="6"
        summary="acquire and release timeline points are in conflict"/>
    </enum>

    <request name="set_acquire_point">
      <description summary="set the acquire timeline point">
        Set the timeline point that must be signalled before the compositor may
        sample from the buffer attached with wl_surface.attach.

        The 64-bit unsigned value combined from point_hi and point_lo is the
        point value.

        The acquire point is double-buffered state, and will be applied on the
        next wl_surface.commit request for the associated surface. Thus, it
        applies only to the buffer that is attached to the surface at commit
        time.

        If an acquire point has already been attached during the same commit
        cycle, the new point replaces the old one.

        If the associated wl_surface was destroyed, a no_surface error is
        raised.

        If at surface commit time there is a pending acquire timeline point set
        but no pending buffer attached, a no_buffer error is raised. If at
        surface commit time there is a pending buffer attached but no pending
        acquire timeline point set, the no_acquire_point protocol error is
        raised.
      </description>
      <arg name="timeline" type="object" interface="wp_linux_drm_syncobj_timeline_v1"/>
      <arg name="point_hi" type="uint" summary="high 32 bits of the point value"/>
      <arg name="point_lo" type="uint" summary="low 32 bits of the point value"/>
    </request>

    <request name="set_release_point">
      <description summary="set the release timeline point">
        Set the timeline point that must be signalled by the compositor when it
        has finished its usage of the buffer attached with wl_surface.attach
        for the relevant commit.

        Once the timeline point is signaled, and assuming the associated buffer
        is not pending release from other wl_surface.commit requests, no
        additional explicit or implicit synchronization with the compositor is
        required to safely re-use the buffer.

        Note that clients cannot rely on the release point being always
        signaled after the acquire point: compositors may release buffers
        without ever reading from them. In addition, the compositor may use
        different presentation paths for different commits, which may have
        different release behavior. As a result, the compositor may signal the
        release points in a different order than the client committed them.

        Because signaling a timeline point also signals every previous point,
        it is generally not safe to use the same timeline object for the
        release points of multiple buffers. The out-of-order signaling
        described above may lead to a release point being signaled before the
        compositor has finished reading. To avoid this, it is strongly
        recommended that each buffer should use a separate timeline for its
        release points.

        The 64-bit unsigned value combined from point_hi and point_lo is the
        point value.

        The release point is double-buffered state, and will be applied on the
        next wl_surface.commit request for the associated surface. Thus, it
        applies only to the buffer that is attached to the surface at commit
        time.

        If a release point has already been attached during the same commit
        cycle, the new point replaces the old one.

        If the associated wl_surface was destroyed, a no_surface error is
        raised.

        If at surface commit time there is a pending release timeline point set
        but no pending buffer attached, a no_buffer error is raised. If at
        surface commit time there is a pending buffer attached but no pending
        release timeline point set, the no_release_point protocol error is
        raised.
      </description>
      <arg name="timeline" type="object" interface="wp_linux_drm_syncobj_timeline_v1"/>
      <arg name="point_hi" type="uint" summary="high 32 bits of the point value"/>
      <arg name="point_lo" type="uint" summary="low 32 bits of the point value"/>
    </request>
  </interface>
</protocol>