weston/protocol/linux-dmabuf.xml

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

  <copyright>
    Copyright © 2014, 2015 Collabora, Ltd.

    Permission to use, copy, modify, distribute, and sell this
    software and its documentation for any purpose is hereby granted
    without fee, provided that the above copyright notice appear in
    all copies and that both that copyright notice and this permission
    notice appear in supporting documentation, and that the name of
    the copyright holders not be used in advertising or publicity
    pertaining to distribution of the software without specific,
    written prior permission.  The copyright holders make no
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    purpose.  It is provided "as is" without express or implied
    warranty.

    THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS
    SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
    FITNESS, IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY
    SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
    AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
    ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
    THIS SOFTWARE.
  </copyright>

  <interface name="zlinux_dmabuf" version="1">
    <description summary="factory for creating dmabuf-based wl_buffers">
      Following the interfaces from:
      https://www.khronos.org/registry/egl/extensions/EXT/EGL_EXT_image_dma_buf_import.txt
      and the Linux DRM sub-system's AddFb2 ioctl.

      This interface offers a way to create generic dmabuf-based
      wl_buffers. Immediately after a client binds to this interface,
      the set of supported formats is sent with 'format' events.

      The following are required from clients:

      - Clients must ensure that either all data in the dma-buf is
        coherent for all subsequent read access or that coherency is
        correctly handled by the underlying kernel-side dma-buf
        implementation.

      - Don't make any more attachments after sending the buffer to the
        compositor. Making more attachments later increases the risk of
        the compositor not being able to use (re-import) an existing
        dmabuf-based wl_buffer.

      The underlying graphics stack must ensure the following:

      - The dmabuf file descriptors relayed to the server will stay valid
        for the whole lifetime of the wl_buffer. This means the server may
        at any time use those fds to import the dmabuf into any kernel
        sub-system that might accept it.

      To create a wl_buffer from one or more dmabufs, a client creates a
      zlinux_dmabuf_params object with zlinux_dmabuf.create_params
      request. All planes required by the intended format are added with
      the 'add' request. Finally, 'create' request is issued. The server
      will reply with either 'created' event which provides the final
      wl_buffer or 'failed' event saying that it cannot use the dmabufs
      provided.
    </description>

    <request name="destroy" type="destructor">
      <description summary="unbind the factory">
        Objects created through this interface, especially wl_buffers, will
        remain valid.
      </description>
    </request>

    <request name="create_params">
      <description summary="create a temporary object for buffer parameters">
        This temporary object is used to collect multiple dmabuf handles into
        a single batch to create a wl_buffer. It can only be used once and
        should be destroyed after an 'created' or 'failed' event has been
        received.
      </description>
      <arg name="params_id" type="new_id" interface="zlinux_buffer_params"
           summary="the new temporary"/>
    </request>

    <event name="format">
      <description summary="supported buffer format">
        This event advertises one buffer format that the server supports.
        All the supported formats are advertised once when the client
        binds to this interface. A roundtrip after binding guarantees,
        that the client has received all supported formats.

        For the definition of the format codes, see create request.

        XXX: Can a compositor ever enumerate them?
      </description>
      <arg name="format" type="uint" summary="DRM_FORMAT code"/>
    </event>

  </interface>

  <interface name="zlinux_buffer_params" version="1">
    <description summary="parameters for creating a dmabuf-based wl_buffer">
      This temporary object is a collection of dmabufs and other
      parameters that together form a single logical buffer. The temporary
      object may eventually create one wl_buffer unless cancelled by
      destroying it before requesting 'create'.

      Single-planar formats only require one dmabuf, however
      multi-planar formats may require more than one dmabuf. For all
      formats, 'add' request must be called once per plane (even if the
      underlying dmabuf fd is identical).

      You must use consecutive plane indices ('plane_idx' argument for 'add')
      from zero to the number of planes used by the drm_fourcc format code.
      All planes required by the format must be given exactly once, but can
      be given in any order. Each plane index can be set only once.
    </description>

    <enum name="error">
      <entry name="already_used" value="0"
             summary="the dmabuf_batch object has already been used to create a wl_buffer"/>

      <entry name="plane_idx" value="1"
             summary="plane index out of bounds"/>

      <entry name="plane_set" value="2"
             summary="the plane index was already set"/>

      <entry name="incomplete" value="3"
             summary="missing or too many planes to create a buffer"/>

      <entry name="invalid_format" value="4"
             summary="format not supported"/>

      <entry name="invalid_dimensions" value="5"
             summary="invalid width or height"/>

      <entry name="out_of_bounds" value="6"
             summary="offset + stride * height goes out of dmabuf bounds"/>
    </enum>

    <request name="destroy" type="destructor">
      <description summary="delete this object, used or not">
        Cleans up the temporary data sent to the server for dmabuf-based
        wl_buffer creation.
      </description>
    </request>

    <request name="add">
      <description summary="add a dmabuf to the temporary set">
        This request adds one dmabuf to the set in this zlinux_buffer_params.

        The 64-bit unsigned value combined from modifier_hi and modifier_lo
        is the dmabuf layout modifier. DRM AddFB2 ioctl calls this the
        fb modifier, which is defined in drm_mode.h of Linux UAPI.
        This is an opaque token. Drivers use this token to express tiling,
        compression, etc. driver-specific modifications to the base format
        defined by the DRM fourcc code.

        This request raises the PLANE_IDX error if plane_idx is too large.
        The error PLANE_SET is raised if attempting to set a plane that
        was already set.
      </description>

      <arg name="fd" type="fd" summary="dmabuf fd"/>
      <arg name="plane_idx" type="uint" summary="plane index"/>
      <arg name="offset" type="uint" summary="offset in bytes"/>
      <arg name="stride" type="uint" summary="stride in bytes"/>
      <arg name="modifier_hi" type="uint"
           summary="high 32 bits of layout modifier"/>
      <arg name="modifier_lo" type="uint"
           summary="low 32 bits of layout modifier"/>
    </request>

    <enum name="flags">
      <entry name="y_invert" value="1" summary="contents are y-inverted"/>
      <entry name="interlaced" value="2" summary="content is interlaced"/>
      <entry name="bottom_first" value="4" summary="bottom field first"/>
    </enum>

    <request name="create">
      <description summary="create a wl_buffer from the given dmabufs">
        This asks for creation of a wl_buffer from the added dmabuf
        buffers. The wl_buffer is not created immediately but returned via
        the 'created' event if the dmabuf sharing succeeds. The sharing
        may fail at runtime for reasons a client cannot predict, in
        which case the 'failed' event is triggered.

        The 'format' argument is a DRM_FORMAT code, as defined by the
        libdrm's drm_fourcc.h. The Linux kernel's DRM sub-system is the
        authoritative source on how the format codes should work.

        The 'flags' is a bitfield of the flags defined in enum "flags".
        'y_invert' means the that the image needs to be y-flipped.

        Flag 'interlaced' means that the frame in the buffer is not
        progressive as usual, but interlaced. An interlaced buffer as
        supported here must always contain both top and bottom fields.
        The top field always begins on the first pixel row. The temporal
        ordering between the two fields is top field first, unless
        'bottom_first' is specified. It is undefined whether 'bottom_first'
        is ignored if 'interlaced' is not set.

        This protocol does not convey any information about field rate,
        duration, or timing, other than the relative ordering between the
        two fields in one buffer. A compositor may have to estimate the
        intended field rate from the incoming buffer rate. It is undefined
        whether the time of receiving wl_surface.commit with a new buffer
        attached, applying the wl_surface state, wl_surface.frame callback
        trigger, presentation, or any other point in the compositor cycle
        is used to measure the frame or field times. There is no support
        for detecting missed or late frames/fields/buffers either, and
        there is no support whatsoever for cooperating with interlaced
        compositor output.

        The composited image quality resulting from the use of interlaced
        buffers is explicitly undefined. A compositor may use elaborate
        hardware features or software to deinterlace and create progressive
        output frames from a sequence of interlaced input buffers, or it
        may produce substandard image quality. However, compositors that
        cannot guarantee reasonable image quality in all cases are recommended
        to just reject all interlaced buffers.

        Any argument errors, including non-positive width or height,
        mismatch between the number of planes and the format, bad
        format, bad offset or stride, may be indicated by fatal protocol
        errors: INCOMPLETE, INVALID_FORMAT, INVALID_DIMENSIONS,
        OUT_OF_BOUNDS.

        Dmabuf import errors in the server that are not obvious client
        bugs are returned via the 'failed' event as non-fatal. This
        allows attempting dmabuf sharing and falling back in the client
        if it fails.

        This request can be sent only once in the object's lifetime, after
        which the only legal request is destroy. This object should be
        destroyed after issuing 'create' request. Attempting to use this
        object after issuing 'create' raises ALREADY_USED protocol error.

        It is not mandatory to issue 'create'. If a client wants to
        cancel the buffer creation, it can just destroy this object.
      </description>
      <arg name="width" type="int" summary="base plane width in pixels"/>
      <arg name="height" type="int" summary="base plane height in pixels"/>
      <arg name="format" type="uint" summary="DRM_FORMAT code"/>
      <arg name="flags" type="uint" summary="see enum flags"/>
    </request>

    <event name="created">
      <description summary="buffer creation succeeded">
        This event indicates that the attempted buffer creation was
        successful. It provides the new wl_buffer referencing the dmabuf(s).

        Upon receiving this event, the client should destroy the
        zlinux_dmabuf_params object.
      </description>
      <arg name="buffer" type="new_id" interface="wl_buffer"
           summary="the newly created wl_buffer"/>
    </event>

    <event name="failed">
      <description summary="buffer creation failed">
        This event indicates that the attempted buffer creation has
        failed. It usually means that one of the dmabuf constraints
        has not been fulfilled.

        Upon receiving this event, the client should destroy the
        zlinux_buffer_params object.
      </description>
    </event>

  </interface>

</protocol>