modesetting: Implement PRIME syncing as a sink

Implements (Enable/Disable)SharedPixmapFlipping and
SharedPixmapNotifyDamage, the sink functions for PRIME synchronization and
double buffering. Allows modesetting driver to be used as a sink with PRIME
synchronization.

Changes dispatch_slave_dirty to flush damage from both scanout pixmaps.

Changes drmmode_set_scanout_pixmap*() functions to
drmmode_set_target_scanout_pixmap*() that take an additional parameter
PixmapPtr *target. Then, treat *target as it did prime_pixmap. This allows
me to use it to explicitly set both prime_pixmap and prime_pixmap_back
individually. drmmode_set_scanout_pixmap() without the extra parameter
remains to cover the single-buffered case, but only works if we aren't
already double buffered.

driver.c:
    Add plumbing for rr(Enable/Disable)SharedPixmapFlipping and
    SharedPixmapNotifyDamage.

    Change dispatch_dirty_crtc to dispatch_dirty_pixmap, which functions the
    same but flushes damage associated with a ppriv instead of the crtc, and
    chanage dispatch_slave_dirty to use it on both scanout pixmaps if
    applicable.

drmmode_display.h:
    Add flip_seq field to msPixmapPrivRec to keep track of the event handler
    associated with a given pixmap, if any.

    Add wait_for_damage field to msPixmapPrivRec to keep track if we have
    requested a damage notification from the source.

    Add enable_flipping field to drmmode_crtc_private_rec to keep track if
    flipping is enabled or disabled.

    Add prime_pixmap_back to drmmode_crtc_private_rec to keep track of back
    buffer internally.

    Add declarations for drmmode_SetupPageFlipFence(),
    drmmode_EnableSharedPixmapFlipping(),
    drmmode_DisableSharedPixmapFlipping, drmmode_SharedPixmapFlip(), and
    drmmode_SharedPixmapPresentOnVBlank().

    Move slave damage from crtc to ppriv.

drmmode_display.c:
    Change drmmode_set_scanout_pixmap*() functions to
    drmmode_set_target_scanout_pixmap*() that take an additional parameter
    PixmapPtr *target for explicitly setting different scanout pixmaps.

    Add definitions for functions drmmode_SharedPixmapFlip(),
    drmmode_SharedPixmapPresentOnVBlank(),
    drmmode_SharedPixmapPresent(),
    drmmode_SharedPixmapVBlankEventHandler(),
    drmmode_SharedPixmapVBlankEventAbort(),
    drmmode_EnableSharedPixmapFlipping(), and
    drmmode_DisableSharedPixmapFlipping,
    drmmode_InitSharedPixmapFlipping(), and
    drmmode_FiniSharedPixmapFlipping, along with struct
    vblank_event_args.

    The control flow is as follows:
        pScrPriv->rrEnableSharedPixmapFlipping() makes its way to
        drmmode_EnableSharedPixmapFlipping(), which sets enable_flipping to
        TRUE and sets both scanout pixmaps prime_pixmap and
        prime_pixmap_back.

        When setting a mode, if prime_pixmap is defined, modesetting
        driver will call drmmode_InitSharedPixmapFlipping(), which if
        flipping is enabled will call drmmode_SharedPixmapPresent() on
        scanout_pixmap_back.

        drmmode_SharedPixmapPresent() requests that for the source to
        present on the given buffer using master->PresentSharedPixmap(). If
        it succeeds, it will then attempt to flip to that buffer using
        drmmode_SharedPixmapFlip(). Flipping shouldn't fail, but if it
        does, it will raise a warning and try drmmode_SharedPixmapPresent()
        again on the next vblank using
        drmmode_SharedPixmapPresentOnVBlank().

        master->PresentSharedPixmap() could fail, in most cases because
        there is no outstanding damage on the mscreenpix tracked by the
        shared pixmap. In this case, drmmode_SharedPixmapPresent() will
        attempt to use master->RequestSharedPixmapNotifyDamage() to request
        for the source driver to call slave->SharedPixmapNotifyDamage() in
        response to damage on mscreenpix. This will ultimately call
        into drmmode_SharedPixmapPresentOnVBlank() to retry
        drmmode_SharedPixmapPresent() on the next vblank after
        accumulating damage.

        drmmode_SharedPixmapFlip() sets up page flip event handler by
        packing struct vblank_event_args with the necessary parameters, and
        registering drmmode_SharedPixmapVBlankEventHandler() and
        drmmode_SharedPixmapVBlankEventAbort() with the modesetting DRM
        event handler queue. Then, it uses the drmModePageFlip() to flip on
        the next vblank and raise an event.

        drmmode_SharedPixmapPresentOnVBlank() operates similarly to
        drmmode_SharedPixmapFlip(), but uses drmWaitVBlank() instead of
        drmModePageFlip() to raise the event without flipping.

        On the next vblank, DRM will raise an event that will ultimately be
        handled by drmmode_SharedPixmapVBlankEventHandler(). If we flipped,
        it will update prime_pixmap and prime_pixmap_back to reflect that
        frontTarget is now being displayed, and use
        drmmode_SharedPixmapPresent(backTarget) to start the process again
        on the now-hidden shared pixmap. If we didn't flip, it will just
        use drmmode_SharedPixmapPresent(frontTarget) to start the process
        again on the still-hidden shared pixmap.

        Note that presentation generally happens asynchronously, so with
        these changes alone tearing is reduced, but we can't always
        guarantee that the present will finish before the flip. These
        changes are meant to be paired with changes to the sink DRM driver
        that makes flips wait on fences attached to dmabuf backed buffers.
        The source driver is responsible for attaching the fences and
        signaling them when presentation is finished.

        Note that because presentation is requested in response to a
        vblank, PRIME sources will now conform to the sink's refresh rate.

        At teardown, pScrPriv->rrDisableSharedPixmapFlipping() will be
        called, making its way to drmmode_FiniSharedPixmapFlipping().
        There, the event handlers for prime_pixmap and prime_pixmap_back
        are aborted, freeing the left over parameter structure. Then,
        prime_pixmap and prime_pixmap back are unset as scanout pixmaps.

    Register and tear down slave damage per-scanout pixmap instead of
    per-crtc.

v1: Initial commit
v2: Renamed PresentTrackedFlippingPixmap to PresentSharedPixmap
    Renamed flipSeq to flip_seq
    Warn if flip failed
    Use SharedPixmapNotifyDamage to retry on next vblank after damage
v3: Refactor to accomodate moving (rr)StartFlippingPixmapTracking and
    (rr)(Enable/Disable)SharedPixmapFlipping to rrScrPrivRec from ScreenRec
    Do damage tracking on both scanout pixmaps
v4: Tweaks to commit message
v5: Revise for internal storage of prime pixmap ptrs
    Move disabling for reverse PRIME from source commit to here
    Use drmmode_set_target_scanout_pixmap*() to set scanout pixmaps
    internally to EnableSharedPixmapFlipping().
    Don't support flipping if ms->drmmode.pageflip == FALSE.
    Move flipping_active check to this commit
v6: Rebase onto ToT
v7: Unchanged

Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Alex Goins <agoins@nvidia.com>