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    Subject[RFC PATCH 00/11] Introduce writeback connectors
    Date
    Hi,

    This RFC series introduces a new connector type:
    DRM_MODE_CONNECTOR_WRITEBACK
    It is a follow-on from a previous discussion: [1]

    Writeback connectors are used to expose the memory writeback engines
    found in some display controllers, which can write a CRTC's
    composition result to a memory buffer.
    This is useful e.g. for testing, screen-recording, screenshots,
    wireless display, display cloning, memory-to-memory composition.

    Patches 1-7 include the core framework changes required, and patches
    8-11 implement a writeback connector for the Mali-DP writeback engine.
    The Mali-DP patches depend on this other series: [2].

    The connector is given the FB_ID property for the output framebuffer,
    and two new read-only properties: PIXEL_FORMATS and
    PIXEL_FORMATS_SIZE, which expose the supported framebuffer pixel
    formats of the engine.

    The EDID property is not exposed for writeback connectors.

    Writeback connector usage:
    --------------------------
    Due to connector routing changes being treated as "full modeset"
    operations, any client which wishes to use a writeback connector
    should include the connector in every modeset. The writeback will not
    actually become active until a framebuffer is attached.

    The writeback itself is enabled by attaching a framebuffer to the
    FB_ID property of the connector. The driver must then ensure that the
    CRTC content of that atomic commit is written into the framebuffer.

    The writeback works in a one-shot mode with each atomic commit. This
    prevents the same content from being written multiple times.
    In some cases (front-buffer rendering) there might be a desire for
    continuous operation - I think a property could be added later for
    this kind of control.

    Writeback can be disabled by setting FB_ID to zero.

    Known issues:
    -------------
    * I'm not sure what "DPMS" should mean for writeback connectors.
    It could be used to disable writeback (even when a framebuffer is
    attached), or it could be hidden entirely (which would break the
    legacy DPMS call for writeback connectors).
    * With Daniel's recent re-iteration of the userspace API rules, I
    fully expect to provide some userspace code to support this. The
    question is what, and where? We want to use writeback for testing,
    so perhaps some tests in igt is suitable.
    * Documentation. Probably some portion of this cover letter needs to
    make it into Documentation/
    * Synchronisation. Our hardware will finish the writeback by the next
    vsync. I've not implemented fence support here, but it would be an
    obvious addition.

    See Also:
    ---------
    [1] https://lists.freedesktop.org/archives/dri-devel/2016-July/113197.html
    [2] https://lists.freedesktop.org/archives/dri-devel/2016-October/120486.html

    I welcome any comments, especially if this approach does/doesn't fit
    well with anyone else's hardware.

    Thanks,

    -Brian

    ---

    Brian Starkey (10):
    drm: add writeback connector type
    drm/fb-helper: skip writeback connectors
    drm: extract CRTC/plane disable from drm_framebuffer_remove
    drm: add __drm_framebuffer_remove_atomic
    drm: add fb to connector state
    drm: expose fb_id property for writeback connectors
    drm: add writeback-connector pixel format properties
    drm: mali-dp: rename malidp_input_format
    drm: mali-dp: add RGB writeback formats for DP550/DP650
    drm: mali-dp: add writeback connector

    Liviu Dudau (1):
    drm: mali-dp: Add support for writeback on DP550/DP650

    drivers/gpu/drm/arm/Makefile | 1 +
    drivers/gpu/drm/arm/malidp_crtc.c | 10 ++
    drivers/gpu/drm/arm/malidp_drv.c | 25 +++-
    drivers/gpu/drm/arm/malidp_drv.h | 5 +
    drivers/gpu/drm/arm/malidp_hw.c | 104 ++++++++++----
    drivers/gpu/drm/arm/malidp_hw.h | 27 +++-
    drivers/gpu/drm/arm/malidp_mw.c | 268 +++++++++++++++++++++++++++++++++++
    drivers/gpu/drm/arm/malidp_planes.c | 8 +-
    drivers/gpu/drm/arm/malidp_regs.h | 15 ++
    drivers/gpu/drm/drm_atomic.c | 40 ++++++
    drivers/gpu/drm/drm_atomic_helper.c | 4 +
    drivers/gpu/drm/drm_connector.c | 79 ++++++++++-
    drivers/gpu/drm/drm_crtc.c | 14 +-
    drivers/gpu/drm/drm_fb_helper.c | 4 +
    drivers/gpu/drm/drm_framebuffer.c | 249 ++++++++++++++++++++++++++++----
    drivers/gpu/drm/drm_ioctl.c | 7 +
    include/drm/drmP.h | 2 +
    include/drm/drm_atomic.h | 3 +
    include/drm/drm_connector.h | 15 ++
    include/drm/drm_crtc.h | 12 ++
    include/uapi/drm/drm.h | 10 ++
    include/uapi/drm/drm_mode.h | 1 +
    22 files changed, 830 insertions(+), 73 deletions(-)
    create mode 100644 drivers/gpu/drm/arm/malidp_mw.c

    --
    1.7.9.5

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