protocol/weston-direct-display.xml

<?xml version="1.0" encoding="UTF-8"?>
<protocol name="weston_direct_display">

  <copyright>
    Copyright © 2019 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="weston_direct_display_v1" version="1">
    <description summary="weston direct display">
      Weston extension to instruct the compositor to avoid any import
      of the dmabuf created by 'linux-dmabuf' protocol other than the display
      controller.

      Compositors are already going to use direct scan-out as much as possible but
      there's no assurance that while doing so, they won't first import the dmabuf
      in to the GPU. This extension assures the client that the compositor will
      never attempt to import in to the GPU and pass it directly to the display
      controller.

      Clients can make use of this extension to pass the dmabuf buffer to the
      display controller, potentially increasing the performance and lowering the
      bandwidth usage.

      Lastly, clients can make use of this extension in tandem with content-protection
      one thus avoiding any GPU interaction and providing a secure-content path.
      Also, in some cases, the memory where dmabuf are allocated are in specially
      crafted memory zone which would be seen as an illegal memory access when the
      GPU will attempt to read it.

      WARNING: This interface by design might break screenshoting functionality
      as compositing might be involved while doing that. Also, do note, that in
      case the dmabufer provided can't be imported by KMS, the client connection
      will be terminated.

      WARNING: This extension requires 'linux-dmabuf' protocol and
      'zwp_linux_buffer_params_v1' be already created by 'zwp_linux_buffer_v1'.
    </description>

    <request name="enable">
      <description summary="forward buffer to display controller">
      This request tells the compositor not to import the dmabuf to the GPU
      in order to bypass it entirely, such that the buffer will be directly
      scanned-out by the display controller. If HW is not capable/or there
      aren't any available resources to directly scan-out the buffer, a
      placeholder should be installed in-place by the compositor. The
      compositor may perform checks on the dmabuf and refuse to create a
      wl_buffer if the dmabuf seems unusable for being used directly.

      Assumes that 'zwp_linux_buffer_params_v1' was already created
      by 'zwp_linux_dmabuf_v1_create_params'.
      </description>
      <arg name="dmabuf" type="object" interface="zwp_linux_buffer_params_v1"
           summary="enable direct-display for dmabuf buffer"/>
    </request>

    <request name="destroy" type="destructor">
      <description summary="destroy factory object">
        Destroys the factory object, but does not affect any other objects.
      </description>
    </request>
  </interface>

</protocol>