Add zwp_linux_explicit_synchronization_v1

This protocol enables explicit synchronization of asynchronous graphics
operations on buffers on a per-commit basis. Support is currently
limited to dmabuf buffers and dma_fence fence FDs.

Explicit synchronization provides a more versatile notification
mechanism for buffer readiness and availability, and can be used to
improve efficiency by integrating with related functionality in display
and graphics APIs.

This protocol is also useful in ChromeOS ARC++ (running Android apps
inside ChromeOS, using Wayland as the communication protocol), where it
can enable integration of the ChromeOS compositor with the explicit
synchronization mechanisms of the Android display subsystem.

Finally, the per-commit nature of the release events provided by this
protocol potentially offers a solution to a deficiency of the
wl_buffer.release event (see
https://gitlab.freedesktop.org/wayland/wayland/issues/46).

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniels@collabora.com>
[Pekka: dropped Reveman from maintainers]
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

3 files changed, 241 insertions, 0 deletions

diff --git a/Makefile.am b/Makefile.am
index 6394e26..7dfbb9e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -21,6 +21,7 @@ unstable_protocols =								\
 	unstable/xdg-output/xdg-output-unstable-v1.xml				\
 	unstable/input-timestamps/input-timestamps-unstable-v1.xml	\
 	unstable/xdg-decoration/xdg-decoration-unstable-v1.xml	\
+	unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml \
 	$(NULL)
 
 stable_protocols =								\
diff --git a/unstable/linux-explicit-synchronization/README b/unstable/linux-explicit-synchronization/README
new file mode 100644
index 0000000..59bcb6f
--- /dev/null
+++ b/unstable/linux-explicit-synchronization/README
@@ -0,0 +1,5 @@
+Linux explicit synchronization (dma-fence) protocol
+
+Maintainers:
+Daniel Stone <daniels@collabora.com>
+Alexandros Frantzis <alexandros.frantzis@collabora.com>
diff --git a/unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml b/unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml
new file mode 100644
index 0000000..db36284
--- /dev/null
+++ b/unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml
@@ -0,0 +1,235 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="zwp_linux_explicit_synchronization_unstable_v1">
+
+  <copyright>
+    Copyright 2016 The Chromium Authors.
+    Copyright 2017 Intel Corporation
+    Copyright 2018 Collabora, Ltd
+
+    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>
+
+  <interface name="zwp_linux_explicit_synchronization_v1" version="1">
+    <description summary="protocol for providing explicit synchronization">
+      This global is a factory interface, allowing clients to request
+      explicit synchronization for buffers on a per-surface basis.
+
+      See zwp_linux_surface_synchronization_v1 for more information.
+
+      This interface is derived from Chromium's
+      zcr_linux_explicit_synchronization_v1.
+
+      Warning! The protocol described in this file is experimental and
+      backward incompatible changes may be made. Backward compatible changes
+      may be added together with the corresponding interface version bump.
+      Backward incompatible changes are done by bumping the version number in
+      the protocol and interface names and resetting the interface version.
+      Once the protocol is to be declared stable, the 'z' prefix and the
+      version number in the protocol and interface names are removed and the
+      interface version number is reset.
+    </description>
+
+    <request name="destroy" type="destructor">
+      <description summary="destroy explicit synchronization factory object">
+        Destroy this explicit synchronization factory object. Other objects,
+        including zwp_linux_surface_synchronization_v1 objects created by this
+        factory, shall not be affected by this request.
+      </description>
+    </request>
+
+    <enum name="error">
+      <entry name="synchronization_exists" value="0"
+             summary="the surface already has a synchronization object associated"/>
+    </enum>
+
+    <request name="get_synchronization">
+      <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 synchronization_exists protocol error is raised.
+      </description>
+
+      <arg name="id" type="new_id"
+           interface="zwp_linux_surface_synchronization_v1"
+           summary="the new synchronization interface id"/>
+      <arg name="surface" type="object" interface="wl_surface"
+           summary="the surface"/>
+    </request>
+  </interface>
+
+  <interface name="zwp_linux_surface_synchronization_v1" version="1">
+    <description summary="per-surface explicit synchronization support">
+      This object implements per-surface explicit synchronization.
+
+      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.
+
+      In 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, in explicit synchronization, dma_fence objects mark when the
+      asynchronous operations are complete. When submitting a buffer, the
+      client provides an acquire fence which will be waited on before the
+      compositor accesses the buffer. The Wayland server, through a
+      zwp_linux_buffer_release_v1 object, will inform the client with an event
+      which may be accompanied by a release fence, when the compositor will no
+      longer access the buffer contents due to the specific commit that
+      requested the release event.
+
+      Each surface can be associated with only one object of this interface at
+      any time.
+
+      Explicit synchronization is guaranteed to be supported only for buffers
+      created with any version of the wp_linux_dmabuf buffer factory.
+    </description>
+
+    <request name="destroy" type="destructor">
+      <description summary="destroy synchronization object">
+        Destroy this explicit synchronization object.
+
+        Any fence set by this object with set_acquire_fence since the last
+        commit will be discarded by the server. Any fences set by this object
+        before the last commit are not affected.
+
+        zwp_linux_buffer_release_v1 objects created by this object are not
+        affected by this request.
+      </description>
+    </request>
+
+    <enum name="error">
+      <entry name="invalid_fence" value="0"
+             summary="the fence specified by the client could not be imported"/>
+      <entry name="duplicate_fence" value="1"
+             summary="multiple fences added for a single surface commit"/>
+      <entry name="duplicate_release" value="2"
+             summary="multiple releases added for a single surface commit"/>
+      <entry name="no_surface" value="3"
+             summary="the associated wl_surface was destroyed"/>
+      <entry name="unsupported_buffer" value="4"
+             summary="the buffer does not support explicit synchronization"/>
+      <entry name="no_buffer" value="5"
+             summary="no buffer was attached"/>
+    </enum>
+
+    <request name="set_acquire_fence">
+      <description summary="set the acquire fence">
+        Set the acquire fence that must be signaled before the compositor
+        may sample from the buffer attached with wl_surface.attach. The fence
+        is a dma_fence kernel object.
+
+        The acquire fence 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 the provided fd is not a valid dma_fence fd, then an INVALID_FENCE
+        error is raised.
+
+        If a fence has already been attached during the same commit cycle, a
+        DUPLICATE_FENCE error is raised.
+
+        If the associated wl_surface was destroyed, a NO_SURFACE error is
+        raised.
+
+        If at surface commit time the attached buffer does not support explicit
+        synchronization, an UNSUPPORTED_BUFFER error is raised.
+
+        If at surface commit time there is no buffer attached, a NO_BUFFER
+        error is raised.
+      </description>
+      <arg name="fd" type="fd" summary="acquire fence fd"/>
+    </request>
+
+    <request name="get_release">
+      <description summary="release fence for last-attached buffer">
+        Create a listener for the release of the buffer attached by the
+        client with wl_surface.attach. See zwp_linux_buffer_release_v1
+        documentation for more information.
+
+        The release object is double-buffered state, and will be associated
+        with the buffer that is attached to the surface at wl_surface.commit
+        time.
+
+        If a zwp_linux_buffer_release_v1 object has already been requested for
+        the surface in the same commit cycle, a DUPLICATE_RELEASE error is
+        raised.
+
+        If the associated wl_surface was destroyed, a NO_SURFACE error
+        is raised.
+
+        If at surface commit time there is no buffer attached, a NO_BUFFER
+        error is raised.
+      </description>
+      <arg name="release" type="new_id" interface="zwp_linux_buffer_release_v1"
+           summary="new zwp_linux_buffer_release_v1 object"/>
+    </request>
+  </interface>
+
+  <interface name="zwp_linux_buffer_release_v1" version="1">
+    <description summary="buffer release explicit synchronization">
+      This object is instantiated in response to a
+      zwp_linux_surface_synchronization_v1.get_release request.
+
+      It provides an alternative to wl_buffer.release events, providing a
+      unique release from a single wl_surface.commit request. The release event
+      also supports explicit synchronization, providing a fence FD for the
+      client to synchronize against.
+
+      Exactly one event, either a fenced_release or an immediate_release, will
+      be emitted for the wl_surface.commit request. The compositor can choose
+      release by release which event it uses.
+
+      This event does not replace wl_buffer.release events; servers are still
+      required to send those events.
+
+      Once a buffer release object has delivered a 'fenced_release' or an
+      'immediate_release' event it is automatically destroyed.
+    </description>
+
+    <event name="fenced_release">
+      <description summary="release buffer with fence">
+        Sent when the compositor has finalised its usage of the associated
+        buffer for the relevant commit, providing a dma_fence which will be
+        signaled when all operations by the compositor on that buffer for that
+        commit have finished.
+
+        This event destroys the zwp_linux_buffer_release_v1 object.
+      </description>
+      <arg name="fence" type="fd" summary="fence for last operation on buffer"/>
+    </event>
+
+    <event name="immediate_release">
+      <description summary="release buffer immediately">
+        Sent when the compositor has finalised its usage of the associated
+        buffer for the relevant commit, and either performed no operations
+        using it, or has a guarantee that all its operations on that buffer for
+        that commit have finished.
+
+        This event destroys the zwp_linux_buffer_release_v1 object.
+      </description>
+    </event>
+  </interface>
+
+</protocol>