RDMA/rtrs: server: Fix some error return code

[linux/fpc-iii.git] / include / drm / drm_modeset_helper_vtables.h

/*
 * Copyright © 2006 Keith Packard
 * Copyright © 2007-2008 Dave Airlie
 * Copyright © 2007-2008 Intel Corporation
 *   Jesse Barnes <jesse.barnes@intel.com>
 * Copyright © 2011-2013 Intel Corporation
 * Copyright © 2015 Intel Corporation
 *   Daniel Vetter <daniel.vetter@ffwll.ch>
 *
 * 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 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 COPYRIGHT HOLDER(S) OR AUTHOR(S) 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.
 */

#ifndef __DRM_MODESET_HELPER_VTABLES_H__
#define __DRM_MODESET_HELPER_VTABLES_H__

#include <drm/drm_crtc.h>
#include <drm/drm_encoder.h>

/**
 * DOC: overview
 *
 * The DRM mode setting helper functions are common code for drivers to use if
 * they wish.  Drivers are not forced to use this code in their
 * implementations but it would be useful if the code they do use at least
 * provides a consistent interface and operation to userspace. Therefore it is
 * highly recommended to use the provided helpers as much as possible.
 *
 * Because there is only one pointer per modeset object to hold a vfunc table
 * for helper libraries they are by necessity shared among the different
 * helpers.
 *
 * To make this clear all the helper vtables are pulled together in this location here.
 */

enum mode_set_atomic;
struct drm_writeback_connector;
struct drm_writeback_job;

/**
 * struct drm_crtc_helper_funcs - helper operations for CRTCs
 *
 * These hooks are used by the legacy CRTC helpers, the transitional plane
 * helpers and the new atomic modesetting helpers.
 */
struct drm_crtc_helper_funcs {
        /**
         * @dpms:
         *
         * Callback to control power levels on the CRTC.  If the mode passed in
         * is unsupported, the provider must use the next lowest power level.
         * This is used by the legacy CRTC helpers to implement DPMS
         * functionality in drm_helper_connector_dpms().
         *
         * This callback is also used to disable a CRTC by calling it with
         * DRM_MODE_DPMS_OFF if the @disable hook isn't used.
         *
         * This callback is used by the legacy CRTC helpers.  Atomic helpers
         * also support using this hook for enabling and disabling a CRTC to
         * facilitate transitions to atomic, but it is deprecated. Instead
         * @atomic_enable and @atomic_disable should be used.
         */
        void (*dpms)(struct drm_crtc *crtc, int mode);

        /**
         * @prepare:
         *
         * This callback should prepare the CRTC for a subsequent modeset, which
         * in practice means the driver should disable the CRTC if it is
         * running. Most drivers ended up implementing this by calling their
         * @dpms hook with DRM_MODE_DPMS_OFF.
         *
         * This callback is used by the legacy CRTC helpers.  Atomic helpers
         * also support using this hook for disabling a CRTC to facilitate
         * transitions to atomic, but it is deprecated. Instead @atomic_disable
         * should be used.
         */
        void (*prepare)(struct drm_crtc *crtc);

        /**
         * @commit:
         *
         * This callback should commit the new mode on the CRTC after a modeset,
         * which in practice means the driver should enable the CRTC.  Most
         * drivers ended up implementing this by calling their @dpms hook with
         * DRM_MODE_DPMS_ON.
         *
         * This callback is used by the legacy CRTC helpers.  Atomic helpers
         * also support using this hook for enabling a CRTC to facilitate
         * transitions to atomic, but it is deprecated. Instead @atomic_enable
         * should be used.
         */
        void (*commit)(struct drm_crtc *crtc);

        /**
         * @mode_valid:
         *
         * This callback is used to check if a specific mode is valid in this
         * crtc. This should be implemented if the crtc has some sort of
         * restriction in the modes it can display. For example, a given crtc
         * may be responsible to set a clock value. If the clock can not
         * produce all the values for the available modes then this callback
         * can be used to restrict the number of modes to only the ones that
         * can be displayed.
         *
         * This hook is used by the probe helpers to filter the mode list in
         * drm_helper_probe_single_connector_modes(), and it is used by the
         * atomic helpers to validate modes supplied by userspace in
         * drm_atomic_helper_check_modeset().
         *
         * This function is optional.
         *
         * NOTE:
         *
         * Since this function is both called from the check phase of an atomic
         * commit, and the mode validation in the probe paths it is not allowed
         * to look at anything else but the passed-in mode, and validate it
         * against configuration-invariant hardward constraints. Any further
         * limits which depend upon the configuration can only be checked in
         * @mode_fixup or @atomic_check.
         *
         * RETURNS:
         *
         * drm_mode_status Enum
         */
        enum drm_mode_status (*mode_valid)(struct drm_crtc *crtc,
                                           const struct drm_display_mode *mode);

        /**
         * @mode_fixup:
         *
         * This callback is used to validate a mode. The parameter mode is the
         * display mode that userspace requested, adjusted_mode is the mode the
         * encoders need to be fed with. Note that this is the inverse semantics
         * of the meaning for the &drm_encoder and &drm_bridge_funcs.mode_fixup
         * vfunc. If the CRTC cannot support the requested conversion from mode
         * to adjusted_mode it should reject the modeset. See also
         * &drm_crtc_state.adjusted_mode for more details.
         *
         * This function is used by both legacy CRTC helpers and atomic helpers.
         * With atomic helpers it is optional.
         *
         * NOTE:
         *
         * This function is called in the check phase of atomic modesets, which
         * can be aborted for any reason (including on userspace's request to
         * just check whether a configuration would be possible). Atomic drivers
         * MUST NOT touch any persistent state (hardware or software) or data
         * structures except the passed in adjusted_mode parameter.
         *
         * This is in contrast to the legacy CRTC helpers where this was
         * allowed.
         *
         * Atomic drivers which need to inspect and adjust more state should
         * instead use the @atomic_check callback, but note that they're not
         * perfectly equivalent: @mode_valid is called from
         * drm_atomic_helper_check_modeset(), but @atomic_check is called from
         * drm_atomic_helper_check_planes(), because originally it was meant for
         * plane update checks only.
         *
         * Also beware that userspace can request its own custom modes, neither
         * core nor helpers filter modes to the list of probe modes reported by
         * the GETCONNECTOR IOCTL and stored in &drm_connector.modes. To ensure
         * that modes are filtered consistently put any CRTC constraints and
         * limits checks into @mode_valid.
         *
         * RETURNS:
         *
         * True if an acceptable configuration is possible, false if the modeset
         * operation should be rejected.
         */
        bool (*mode_fixup)(struct drm_crtc *crtc,
                           const struct drm_display_mode *mode,
                           struct drm_display_mode *adjusted_mode);

        /**
         * @mode_set:
         *
         * This callback is used by the legacy CRTC helpers to set a new mode,
         * position and framebuffer. Since it ties the primary plane to every
         * mode change it is incompatible with universal plane support. And
         * since it can't update other planes it's incompatible with atomic
         * modeset support.
         *
         * This callback is only used by CRTC helpers and deprecated.
         *
         * RETURNS:
         *
         * 0 on success or a negative error code on failure.
         */
        int (*mode_set)(struct drm_crtc *crtc, struct drm_display_mode *mode,
                        struct drm_display_mode *adjusted_mode, int x, int y,
                        struct drm_framebuffer *old_fb);

        /**
         * @mode_set_nofb:
         *
         * This callback is used to update the display mode of a CRTC without
         * changing anything of the primary plane configuration. This fits the
         * requirement of atomic and hence is used by the atomic helpers. It is
         * also used by the transitional plane helpers to implement a
         * @mode_set hook in drm_helper_crtc_mode_set().
         *
         * Note that the display pipe is completely off when this function is
         * called. Atomic drivers which need hardware to be running before they
         * program the new display mode (e.g. because they implement runtime PM)
         * should not use this hook. This is because the helper library calls
         * this hook only once per mode change and not every time the display
         * pipeline is suspended using either DPMS or the new "ACTIVE" property.
         * Which means register values set in this callback might get reset when
         * the CRTC is suspended, but not restored.  Such drivers should instead
         * move all their CRTC setup into the @atomic_enable callback.
         *
         * This callback is optional.
         */
        void (*mode_set_nofb)(struct drm_crtc *crtc);

        /**
         * @mode_set_base:
         *
         * This callback is used by the legacy CRTC helpers to set a new
         * framebuffer and scanout position. It is optional and used as an
         * optimized fast-path instead of a full mode set operation with all the
         * resulting flickering. If it is not present
         * drm_crtc_helper_set_config() will fall back to a full modeset, using
         * the @mode_set callback. Since it can't update other planes it's
         * incompatible with atomic modeset support.
         *
         * This callback is only used by the CRTC helpers and deprecated.
         *
         * RETURNS:
         *
         * 0 on success or a negative error code on failure.
         */
        int (*mode_set_base)(struct drm_crtc *crtc, int x, int y,
                             struct drm_framebuffer *old_fb);

        /**
         * @mode_set_base_atomic:
         *
         * This callback is used by the fbdev helpers to set a new framebuffer
         * and scanout without sleeping, i.e. from an atomic calling context. It
         * is only used to implement kgdb support.
         *
         * This callback is optional and only needed for kgdb support in the fbdev
         * helpers.
         *
         * RETURNS:
         *
         * 0 on success or a negative error code on failure.
         */
        int (*mode_set_base_atomic)(struct drm_crtc *crtc,
                                    struct drm_framebuffer *fb, int x, int y,
                                    enum mode_set_atomic);

        /**
         * @disable:
         *
         * This callback should be used to disable the CRTC. With the atomic
         * drivers it is called after all encoders connected to this CRTC have
         * been shut off already using their own
         * &drm_encoder_helper_funcs.disable hook. If that sequence is too
         * simple drivers can just add their own hooks and call it from this
         * CRTC callback here by looping over all encoders connected to it using
         * for_each_encoder_on_crtc().
         *
         * This hook is used both by legacy CRTC helpers and atomic helpers.
         * Atomic drivers don't need to implement it if there's no need to
         * disable anything at the CRTC level. To ensure that runtime PM
         * handling (using either DPMS or the new "ACTIVE" property) works
         * @disable must be the inverse of @atomic_enable for atomic drivers.
         * Atomic drivers should consider to use @atomic_disable instead of
         * this one.
         *
         * NOTE:
         *
         * With legacy CRTC helpers there's a big semantic difference between
         * @disable and other hooks (like @prepare or @dpms) used to shut down a
         * CRTC: @disable is only called when also logically disabling the
         * display pipeline and needs to release any resources acquired in
         * @mode_set (like shared PLLs, or again release pinned framebuffers).
         *
         * Therefore @disable must be the inverse of @mode_set plus @commit for
         * drivers still using legacy CRTC helpers, which is different from the
         * rules under atomic.
         */
        void (*disable)(struct drm_crtc *crtc);

        /**
         * @atomic_check:
         *
         * Drivers should check plane-update related CRTC constraints in this
         * hook. They can also check mode related limitations but need to be
         * aware of the calling order, since this hook is used by
         * drm_atomic_helper_check_planes() whereas the preparations needed to
         * check output routing and the display mode is done in
         * drm_atomic_helper_check_modeset(). Therefore drivers that want to
         * check output routing and display mode constraints in this callback
         * must ensure that drm_atomic_helper_check_modeset() has been called
         * beforehand. This is calling order used by the default helper
         * implementation in drm_atomic_helper_check().
         *
         * When using drm_atomic_helper_check_planes() this hook is called
         * after the &drm_plane_helper_funcs.atomic_check hook for planes, which
         * allows drivers to assign shared resources requested by planes in this
         * callback here. For more complicated dependencies the driver can call
         * the provided check helpers multiple times until the computed state
         * has a final configuration and everything has been checked.
         *
         * This function is also allowed to inspect any other object's state and
         * can add more state objects to the atomic commit if needed. Care must
         * be taken though to ensure that state check and compute functions for
         * these added states are all called, and derived state in other objects
         * all updated. Again the recommendation is to just call check helpers
         * until a maximal configuration is reached.
         *
         * This callback is used by the atomic modeset helpers and by the
         * transitional plane helpers, but it is optional.
         *
         * NOTE:
         *
         * This function is called in the check phase of an atomic update. The
         * driver is not allowed to change anything outside of the free-standing
         * state objects passed-in or assembled in the overall &drm_atomic_state
         * update tracking structure.
         *
         * Also beware that userspace can request its own custom modes, neither
         * core nor helpers filter modes to the list of probe modes reported by
         * the GETCONNECTOR IOCTL and stored in &drm_connector.modes. To ensure
         * that modes are filtered consistently put any CRTC constraints and
         * limits checks into @mode_valid.
         *
         * RETURNS:
         *
         * 0 on success, -EINVAL if the state or the transition can't be
         * supported, -ENOMEM on memory allocation failure and -EDEADLK if an
         * attempt to obtain another state object ran into a &drm_modeset_lock
         * deadlock.
         */
        int (*atomic_check)(struct drm_crtc *crtc,
                            struct drm_crtc_state *state);

        /**
         * @atomic_begin:
         *
         * Drivers should prepare for an atomic update of multiple planes on
         * a CRTC in this hook. Depending upon hardware this might be vblank
         * evasion, blocking updates by setting bits or doing preparatory work
         * for e.g. manual update display.
         *
         * This hook is called before any plane commit functions are called.
         *
         * Note that the power state of the display pipe when this function is
         * called depends upon the exact helpers and calling sequence the driver
         * has picked. See drm_atomic_helper_commit_planes() for a discussion of
         * the tradeoffs and variants of plane commit helpers.
         *
         * This callback is used by the atomic modeset helpers and by the
         * transitional plane helpers, but it is optional.
         */
        void (*atomic_begin)(struct drm_crtc *crtc,
                             struct drm_crtc_state *old_crtc_state);
        /**
         * @atomic_flush:
         *
         * Drivers should finalize an atomic update of multiple planes on
         * a CRTC in this hook. Depending upon hardware this might include
         * checking that vblank evasion was successful, unblocking updates by
         * setting bits or setting the GO bit to flush out all updates.
         *
         * Simple hardware or hardware with special requirements can commit and
         * flush out all updates for all planes from this hook and forgo all the
         * other commit hooks for plane updates.
         *
         * This hook is called after any plane commit functions are called.
         *
         * Note that the power state of the display pipe when this function is
         * called depends upon the exact helpers and calling sequence the driver
         * has picked. See drm_atomic_helper_commit_planes() for a discussion of
         * the tradeoffs and variants of plane commit helpers.
         *
         * This callback is used by the atomic modeset helpers and by the
         * transitional plane helpers, but it is optional.
         */
        void (*atomic_flush)(struct drm_crtc *crtc,
                             struct drm_crtc_state *old_crtc_state);

        /**
         * @atomic_enable:
         *
         * This callback should be used to enable the CRTC. With the atomic
         * drivers it is called before all encoders connected to this CRTC are
         * enabled through the encoder's own &drm_encoder_helper_funcs.enable
         * hook.  If that sequence is too simple drivers can just add their own
         * hooks and call it from this CRTC callback here by looping over all
         * encoders connected to it using for_each_encoder_on_crtc().
         *
         * This hook is used only by atomic helpers, for symmetry with
         * @atomic_disable. Atomic drivers don't need to implement it if there's
         * no need to enable anything at the CRTC level. To ensure that runtime
         * PM handling (using either DPMS or the new "ACTIVE" property) works
         * @atomic_enable must be the inverse of @atomic_disable for atomic
         * drivers.
         *
         * Drivers can use the @old_crtc_state input parameter if the operations
         * needed to enable the CRTC don't depend solely on the new state but
         * also on the transition between the old state and the new state.
         *
         * This function is optional.
         */
        void (*atomic_enable)(struct drm_crtc *crtc,
                              struct drm_crtc_state *old_crtc_state);

        /**
         * @atomic_disable:
         *
         * This callback should be used to disable the CRTC. With the atomic
         * drivers it is called after all encoders connected to this CRTC have
         * been shut off already using their own
         * &drm_encoder_helper_funcs.disable hook. If that sequence is too
         * simple drivers can just add their own hooks and call it from this
         * CRTC callback here by looping over all encoders connected to it using
         * for_each_encoder_on_crtc().
         *
         * This hook is used only by atomic helpers. Atomic drivers don't
         * need to implement it if there's no need to disable anything at the
         * CRTC level.
         *
         * Comparing to @disable, this one provides the additional input
         * parameter @old_crtc_state which could be used to access the old
         * state. Atomic drivers should consider to use this one instead
         * of @disable.
         *
         * This function is optional.
         */
        void (*atomic_disable)(struct drm_crtc *crtc,
                               struct drm_crtc_state *old_crtc_state);

        /**
         * @get_scanout_position:
         *
         * Called by vblank timestamping code.
         *
         * Returns the current display scanout position from a CRTC and an
         * optional accurate ktime_get() timestamp of when the position was
         * measured. Note that this is a helper callback which is only used
         * if a driver uses drm_crtc_vblank_helper_get_vblank_timestamp()
         * for the @drm_crtc_funcs.get_vblank_timestamp callback.
         *
         * Parameters:
         *
         * crtc:
         *     The CRTC.
         * in_vblank_irq:
         *     True when called from drm_crtc_handle_vblank(). Some drivers
         *     need to apply some workarounds for gpu-specific vblank irq
         *     quirks if the flag is set.
         * vpos:
         *     Target location for current vertical scanout position.
         * hpos:
         *     Target location for current horizontal scanout position.
         * stime:
         *     Target location for timestamp taken immediately before
         *     scanout position query. Can be NULL to skip timestamp.
         * etime:
         *     Target location for timestamp taken immediately after
         *     scanout position query. Can be NULL to skip timestamp.
         * mode:
         *     Current display timings.
         *
         * Returns vpos as a positive number while in active scanout area.
         * Returns vpos as a negative number inside vblank, counting the number
         * of scanlines to go until end of vblank, e.g., -1 means "one scanline
         * until start of active scanout / end of vblank."
         *
         * Returns:
         *
         * True on success, false if a reliable scanout position counter could
         * not be read out.
         */
        bool (*get_scanout_position)(struct drm_crtc *crtc,
                                     bool in_vblank_irq, int *vpos, int *hpos,
                                     ktime_t *stime, ktime_t *etime,
                                     const struct drm_display_mode *mode);
};

/**
 * drm_crtc_helper_add - sets the helper vtable for a crtc
 * @crtc: DRM CRTC
 * @funcs: helper vtable to set for @crtc
 */
static inline void drm_crtc_helper_add(struct drm_crtc *crtc,
                                       const struct drm_crtc_helper_funcs *funcs)
{
        crtc->helper_private = funcs;
}

/**
 * struct drm_encoder_helper_funcs - helper operations for encoders
 *
 * These hooks are used by the legacy CRTC helpers, the transitional plane
 * helpers and the new atomic modesetting helpers.
 */
struct drm_encoder_helper_funcs {
        /**
         * @dpms:
         *
         * Callback to control power levels on the encoder.  If the mode passed in
         * is unsupported, the provider must use the next lowest power level.
         * This is used by the legacy encoder helpers to implement DPMS
         * functionality in drm_helper_connector_dpms().
         *
         * This callback is also used to disable an encoder by calling it with
         * DRM_MODE_DPMS_OFF if the @disable hook isn't used.
         *
         * This callback is used by the legacy CRTC helpers.  Atomic helpers
         * also support using this hook for enabling and disabling an encoder to
         * facilitate transitions to atomic, but it is deprecated. Instead
         * @enable and @disable should be used.
         */
        void (*dpms)(struct drm_encoder *encoder, int mode);

        /**
         * @mode_valid:
         *
         * This callback is used to check if a specific mode is valid in this
         * encoder. This should be implemented if the encoder has some sort
         * of restriction in the modes it can display. For example, a given
         * encoder may be responsible to set a clock value. If the clock can
         * not produce all the values for the available modes then this callback
         * can be used to restrict the number of modes to only the ones that
         * can be displayed.
         *
         * This hook is used by the probe helpers to filter the mode list in
         * drm_helper_probe_single_connector_modes(), and it is used by the
         * atomic helpers to validate modes supplied by userspace in
         * drm_atomic_helper_check_modeset().
         *
         * This function is optional.
         *
         * NOTE:
         *
         * Since this function is both called from the check phase of an atomic
         * commit, and the mode validation in the probe paths it is not allowed
         * to look at anything else but the passed-in mode, and validate it
         * against configuration-invariant hardward constraints. Any further
         * limits which depend upon the configuration can only be checked in
         * @mode_fixup or @atomic_check.
         *
         * RETURNS:
         *
         * drm_mode_status Enum
         */
        enum drm_mode_status (*mode_valid)(struct drm_encoder *crtc,
                                           const struct drm_display_mode *mode);

        /**
         * @mode_fixup:
         *
         * This callback is used to validate and adjust a mode. The parameter
         * mode is the display mode that should be fed to the next element in
         * the display chain, either the final &drm_connector or a &drm_bridge.
         * The parameter adjusted_mode is the input mode the encoder requires. It
         * can be modified by this callback and does not need to match mode. See
         * also &drm_crtc_state.adjusted_mode for more details.
         *
         * This function is used by both legacy CRTC helpers and atomic helpers.
         * This hook is optional.
         *
         * NOTE:
         *
         * This function is called in the check phase of atomic modesets, which
         * can be aborted for any reason (including on userspace's request to
         * just check whether a configuration would be possible). Atomic drivers
         * MUST NOT touch any persistent state (hardware or software) or data
         * structures except the passed in adjusted_mode parameter.
         *
         * This is in contrast to the legacy CRTC helpers where this was
         * allowed.
         *
         * Atomic drivers which need to inspect and adjust more state should
         * instead use the @atomic_check callback. If @atomic_check is used,
         * this hook isn't called since @atomic_check allows a strict superset
         * of the functionality of @mode_fixup.
         *
         * Also beware that userspace can request its own custom modes, neither
         * core nor helpers filter modes to the list of probe modes reported by
         * the GETCONNECTOR IOCTL and stored in &drm_connector.modes. To ensure
         * that modes are filtered consistently put any encoder constraints and
         * limits checks into @mode_valid.
         *
         * RETURNS:
         *
         * True if an acceptable configuration is possible, false if the modeset
         * operation should be rejected.
         */
        bool (*mode_fixup)(struct drm_encoder *encoder,
                           const struct drm_display_mode *mode,
                           struct drm_display_mode *adjusted_mode);

        /**
         * @prepare:
         *
         * This callback should prepare the encoder for a subsequent modeset,
         * which in practice means the driver should disable the encoder if it
         * is running. Most drivers ended up implementing this by calling their
         * @dpms hook with DRM_MODE_DPMS_OFF.
         *
         * This callback is used by the legacy CRTC helpers.  Atomic helpers
         * also support using this hook for disabling an encoder to facilitate
         * transitions to atomic, but it is deprecated. Instead @disable should
         * be used.
         */
        void (*prepare)(struct drm_encoder *encoder);

        /**
         * @commit:
         *
         * This callback should commit the new mode on the encoder after a modeset,
         * which in practice means the driver should enable the encoder.  Most
         * drivers ended up implementing this by calling their @dpms hook with
         * DRM_MODE_DPMS_ON.
         *
         * This callback is used by the legacy CRTC helpers.  Atomic helpers
         * also support using this hook for enabling an encoder to facilitate
         * transitions to atomic, but it is deprecated. Instead @enable should
         * be used.
         */
        void (*commit)(struct drm_encoder *encoder);

        /**
         * @mode_set:
         *
         * This callback is used to update the display mode of an encoder.
         *
         * Note that the display pipe is completely off when this function is
         * called. Drivers which need hardware to be running before they program
         * the new display mode (because they implement runtime PM) should not
         * use this hook, because the helper library calls it only once and not
         * every time the display pipeline is suspend using either DPMS or the
         * new "ACTIVE" property. Such drivers should instead move all their
         * encoder setup into the @enable callback.
         *
         * This callback is used both by the legacy CRTC helpers and the atomic
         * modeset helpers. It is optional in the atomic helpers.
         *
         * NOTE:
         *
         * If the driver uses the atomic modeset helpers and needs to inspect
         * the connector state or connector display info during mode setting,
         * @atomic_mode_set can be used instead.
         */
        void (*mode_set)(struct drm_encoder *encoder,
                         struct drm_display_mode *mode,
                         struct drm_display_mode *adjusted_mode);

        /**
         * @atomic_mode_set:
         *
         * This callback is used to update the display mode of an encoder.
         *
         * Note that the display pipe is completely off when this function is
         * called. Drivers which need hardware to be running before they program
         * the new display mode (because they implement runtime PM) should not
         * use this hook, because the helper library calls it only once and not
         * every time the display pipeline is suspended using either DPMS or the
         * new "ACTIVE" property. Such drivers should instead move all their
         * encoder setup into the @enable callback.
         *
         * This callback is used by the atomic modeset helpers in place of the
         * @mode_set callback, if set by the driver. It is optional and should
         * be used instead of @mode_set if the driver needs to inspect the
         * connector state or display info, since there is no direct way to
         * go from the encoder to the current connector.
         */
        void (*atomic_mode_set)(struct drm_encoder *encoder,
                                struct drm_crtc_state *crtc_state,
                                struct drm_connector_state *conn_state);

        /**
         * @detect:
         *
         * This callback can be used by drivers who want to do detection on the
         * encoder object instead of in connector functions.
         *
         * It is not used by any helper and therefore has purely driver-specific
         * semantics. New drivers shouldn't use this and instead just implement
         * their own private callbacks.
         *
         * FIXME:
         *
         * This should just be converted into a pile of driver vfuncs.
         * Currently radeon, amdgpu and nouveau are using it.
         */
        enum drm_connector_status (*detect)(struct drm_encoder *encoder,
                                            struct drm_connector *connector);

        /**
         * @atomic_disable:
         *
         * This callback should be used to disable the encoder. With the atomic
         * drivers it is called before this encoder's CRTC has been shut off
         * using their own &drm_crtc_helper_funcs.atomic_disable hook. If that
         * sequence is too simple drivers can just add their own driver private
         * encoder hooks and call them from CRTC's callback by looping over all
         * encoders connected to it using for_each_encoder_on_crtc().
         *
         * This callback is a variant of @disable that provides the atomic state
         * to the driver. If @atomic_disable is implemented, @disable is not
         * called by the helpers.
         *
         * This hook is only used by atomic helpers. Atomic drivers don't need
         * to implement it if there's no need to disable anything at the encoder
         * level. To ensure that runtime PM handling (using either DPMS or the
         * new "ACTIVE" property) works @atomic_disable must be the inverse of
         * @atomic_enable.
         */
        void (*atomic_disable)(struct drm_encoder *encoder,
                               struct drm_atomic_state *state);

        /**
         * @atomic_enable:
         *
         * This callback should be used to enable the encoder. It is called
         * after this encoder's CRTC has been enabled using their own
         * &drm_crtc_helper_funcs.atomic_enable hook. If that sequence is
         * too simple drivers can just add their own driver private encoder
         * hooks and call them from CRTC's callback by looping over all encoders
         * connected to it using for_each_encoder_on_crtc().
         *
         * This callback is a variant of @enable that provides the atomic state
         * to the driver. If @atomic_enable is implemented, @enable is not
         * called by the helpers.
         *
         * This hook is only used by atomic helpers, it is the opposite of
         * @atomic_disable. Atomic drivers don't need to implement it if there's
         * no need to enable anything at the encoder level. To ensure that
         * runtime PM handling works @atomic_enable must be the inverse of
         * @atomic_disable.
         */
        void (*atomic_enable)(struct drm_encoder *encoder,
                              struct drm_atomic_state *state);

        /**
         * @disable:
         *
         * This callback should be used to disable the encoder. With the atomic
         * drivers it is called before this encoder's CRTC has been shut off
         * using their own &drm_crtc_helper_funcs.disable hook.  If that
         * sequence is too simple drivers can just add their own driver private
         * encoder hooks and call them from CRTC's callback by looping over all
         * encoders connected to it using for_each_encoder_on_crtc().
         *
         * This hook is used both by legacy CRTC helpers and atomic helpers.
         * Atomic drivers don't need to implement it if there's no need to
         * disable anything at the encoder level. To ensure that runtime PM
         * handling (using either DPMS or the new "ACTIVE" property) works
         * @disable must be the inverse of @enable for atomic drivers.
         *
         * For atomic drivers also consider @atomic_disable and save yourself
         * from having to read the NOTE below!
         *
         * NOTE:
         *
         * With legacy CRTC helpers there's a big semantic difference between
         * @disable and other hooks (like @prepare or @dpms) used to shut down a
         * encoder: @disable is only called when also logically disabling the
         * display pipeline and needs to release any resources acquired in
         * @mode_set (like shared PLLs, or again release pinned framebuffers).
         *
         * Therefore @disable must be the inverse of @mode_set plus @commit for
         * drivers still using legacy CRTC helpers, which is different from the
         * rules under atomic.
         */
        void (*disable)(struct drm_encoder *encoder);

        /**
         * @enable:
         *
         * This callback should be used to enable the encoder. With the atomic
         * drivers it is called after this encoder's CRTC has been enabled using
         * their own &drm_crtc_helper_funcs.enable hook.  If that sequence is
         * too simple drivers can just add their own driver private encoder
         * hooks and call them from CRTC's callback by looping over all encoders
         * connected to it using for_each_encoder_on_crtc().
         *
         * This hook is only used by atomic helpers, it is the opposite of
         * @disable. Atomic drivers don't need to implement it if there's no
         * need to enable anything at the encoder level. To ensure that
         * runtime PM handling (using either DPMS or the new "ACTIVE" property)
         * works @enable must be the inverse of @disable for atomic drivers.
         */
        void (*enable)(struct drm_encoder *encoder);

        /**
         * @atomic_check:
         *
         * This callback is used to validate encoder state for atomic drivers.
         * Since the encoder is the object connecting the CRTC and connector it
         * gets passed both states, to be able to validate interactions and
         * update the CRTC to match what the encoder needs for the requested
         * connector.
         *
         * Since this provides a strict superset of the functionality of
         * @mode_fixup (the requested and adjusted modes are both available
         * through the passed in &struct drm_crtc_state) @mode_fixup is not
         * called when @atomic_check is implemented.
         *
         * This function is used by the atomic helpers, but it is optional.
         *
         * NOTE:
         *
         * This function is called in the check phase of an atomic update. The
         * driver is not allowed to change anything outside of the free-standing
         * state objects passed-in or assembled in the overall &drm_atomic_state
         * update tracking structure.
         *
         * Also beware that userspace can request its own custom modes, neither
         * core nor helpers filter modes to the list of probe modes reported by
         * the GETCONNECTOR IOCTL and stored in &drm_connector.modes. To ensure
         * that modes are filtered consistently put any encoder constraints and
         * limits checks into @mode_valid.
         *
         * RETURNS:
         *
         * 0 on success, -EINVAL if the state or the transition can't be
         * supported, -ENOMEM on memory allocation failure and -EDEADLK if an
         * attempt to obtain another state object ran into a &drm_modeset_lock
         * deadlock.
         */
        int (*atomic_check)(struct drm_encoder *encoder,
                            struct drm_crtc_state *crtc_state,
                            struct drm_connector_state *conn_state);
};

/**
 * drm_encoder_helper_add - sets the helper vtable for an encoder
 * @encoder: DRM encoder
 * @funcs: helper vtable to set for @encoder
 */
static inline void drm_encoder_helper_add(struct drm_encoder *encoder,
                                          const struct drm_encoder_helper_funcs *funcs)
{
        encoder->helper_private = funcs;
}

/**
 * struct drm_connector_helper_funcs - helper operations for connectors
 *
 * These functions are used by the atomic and legacy modeset helpers and by the
 * probe helpers.
 */
struct drm_connector_helper_funcs {
        /**
         * @get_modes:
         *
         * This function should fill in all modes currently valid for the sink
         * into the &drm_connector.probed_modes list. It should also update the
         * EDID property by calling drm_connector_update_edid_property().
         *
         * The usual way to implement this is to cache the EDID retrieved in the
         * probe callback somewhere in the driver-private connector structure.
         * In this function drivers then parse the modes in the EDID and add
         * them by calling drm_add_edid_modes(). But connectors that driver a
         * fixed panel can also manually add specific modes using
         * drm_mode_probed_add(). Drivers which manually add modes should also
         * make sure that the &drm_connector.display_info,
         * &drm_connector.width_mm and &drm_connector.height_mm fields are
         * filled in.
         *
         * Virtual drivers that just want some standard VESA mode with a given
         * resolution can call drm_add_modes_noedid(), and mark the preferred
         * one using drm_set_preferred_mode().
         *
         * This function is only called after the @detect hook has indicated
         * that a sink is connected and when the EDID isn't overridden through
         * sysfs or the kernel commandline.
         *
         * This callback is used by the probe helpers in e.g.
         * drm_helper_probe_single_connector_modes().
         *
         * To avoid races with concurrent connector state updates, the helper
         * libraries always call this with the &drm_mode_config.connection_mutex
         * held. Because of this it's safe to inspect &drm_connector->state.
         *
         * RETURNS:
         *
         * The number of modes added by calling drm_mode_probed_add().
         */
        int (*get_modes)(struct drm_connector *connector);

        /**
         * @detect_ctx:
         *
         * Check to see if anything is attached to the connector. The parameter
         * force is set to false whilst polling, true when checking the
         * connector due to a user request. force can be used by the driver to
         * avoid expensive, destructive operations during automated probing.
         *
         * This callback is optional, if not implemented the connector will be
         * considered as always being attached.
         *
         * This is the atomic version of &drm_connector_funcs.detect.
         *
         * To avoid races against concurrent connector state updates, the
         * helper libraries always call this with ctx set to a valid context,
         * and &drm_mode_config.connection_mutex will always be locked with
         * the ctx parameter set to this ctx. This allows taking additional
         * locks as required.
         *
         * RETURNS:
         *
         * &drm_connector_status indicating the connector's status,
         * or the error code returned by drm_modeset_lock(), -EDEADLK.
         */
        int (*detect_ctx)(struct drm_connector *connector,
                          struct drm_modeset_acquire_ctx *ctx,
                          bool force);

        /**
         * @mode_valid:
         *
         * Callback to validate a mode for a connector, irrespective of the
         * specific display configuration.
         *
         * This callback is used by the probe helpers to filter the mode list
         * (which is usually derived from the EDID data block from the sink).
         * See e.g. drm_helper_probe_single_connector_modes().
         *
         * This function is optional.
         *
         * NOTE:
         *
         * This only filters the mode list supplied to userspace in the
         * GETCONNECTOR IOCTL. Compared to &drm_encoder_helper_funcs.mode_valid,
         * &drm_crtc_helper_funcs.mode_valid and &drm_bridge_funcs.mode_valid,
         * which are also called by the atomic helpers from
         * drm_atomic_helper_check_modeset(). This allows userspace to force and
         * ignore sink constraint (like the pixel clock limits in the screen's
         * EDID), which is useful for e.g. testing, or working around a broken
         * EDID. Any source hardware constraint (which always need to be
         * enforced) therefore should be checked in one of the above callbacks,
         * and not this one here.
         *
         * To avoid races with concurrent connector state updates, the helper
         * libraries always call this with the &drm_mode_config.connection_mutex
         * held. Because of this it's safe to inspect &drm_connector->state.
         *
         * RETURNS:
         *
         * Either &drm_mode_status.MODE_OK or one of the failure reasons in &enum
         * drm_mode_status.
         */
        enum drm_mode_status (*mode_valid)(struct drm_connector *connector,
                                           struct drm_display_mode *mode);
        /**
         * @best_encoder:
         *
         * This function should select the best encoder for the given connector.
         *
         * This function is used by both the atomic helpers (in the
         * drm_atomic_helper_check_modeset() function) and in the legacy CRTC
         * helpers.
         *
         * NOTE:
         *
         * In atomic drivers this function is called in the check phase of an
         * atomic update. The driver is not allowed to change or inspect
         * anything outside of arguments passed-in. Atomic drivers which need to
         * inspect dynamic configuration state should instead use
         * @atomic_best_encoder.
         *
         * You can leave this function to NULL if the connector is only
         * attached to a single encoder. In this case, the core will call
         * drm_connector_get_single_encoder() for you.
         *
         * RETURNS:
         *
         * Encoder that should be used for the given connector and connector
         * state, or NULL if no suitable encoder exists. Note that the helpers
         * will ensure that encoders aren't used twice, drivers should not check
         * for this.
         */
        struct drm_encoder *(*best_encoder)(struct drm_connector *connector);

        /**
         * @atomic_best_encoder:
         *
         * This is the atomic version of @best_encoder for atomic drivers which
         * need to select the best encoder depending upon the desired
         * configuration and can't select it statically.
         *
         * This function is used by drm_atomic_helper_check_modeset().
         * If it is not implemented, the core will fallback to @best_encoder
         * (or drm_connector_get_single_encoder() if @best_encoder is NULL).
         *
         * NOTE:
         *
         * This function is called in the check phase of an atomic update. The
         * driver is not allowed to change anything outside of the free-standing
         * state objects passed-in or assembled in the overall &drm_atomic_state
         * update tracking structure.
         *
         * RETURNS:
         *
         * Encoder that should be used for the given connector and connector
         * state, or NULL if no suitable encoder exists. Note that the helpers
         * will ensure that encoders aren't used twice, drivers should not check
         * for this.
         */
        struct drm_encoder *(*atomic_best_encoder)(struct drm_connector *connector,
                                                   struct drm_connector_state *connector_state);

        /**
         * @atomic_check:
         *
         * This hook is used to validate connector state. This function is
         * called from &drm_atomic_helper_check_modeset, and is called when
         * a connector property is set, or a modeset on the crtc is forced.
         *
         * Because &drm_atomic_helper_check_modeset may be called multiple times,
         * this function should handle being called multiple times as well.
         *
         * This function is also allowed to inspect any other object's state and
         * can add more state objects to the atomic commit if needed. Care must
         * be taken though to ensure that state check and compute functions for
         * these added states are all called, and derived state in other objects
         * all updated. Again the recommendation is to just call check helpers
         * until a maximal configuration is reached.
         *
         * NOTE:
         *
         * This function is called in the check phase of an atomic update. The
         * driver is not allowed to change anything outside of the free-standing
         * state objects passed-in or assembled in the overall &drm_atomic_state
         * update tracking structure.
         *
         * RETURNS:
         *
         * 0 on success, -EINVAL if the state or the transition can't be
         * supported, -ENOMEM on memory allocation failure and -EDEADLK if an
         * attempt to obtain another state object ran into a &drm_modeset_lock
         * deadlock.
         */
        int (*atomic_check)(struct drm_connector *connector,
                            struct drm_atomic_state *state);

        /**
         * @atomic_commit:
         *
         * This hook is to be used by drivers implementing writeback connectors
         * that need a point when to commit the writeback job to the hardware.
         * The writeback_job to commit is available in
         * &drm_connector_state.writeback_job.
         *
         * This hook is optional.
         *
         * This callback is used by the atomic modeset helpers.
         */
        void (*atomic_commit)(struct drm_connector *connector,
                              struct drm_connector_state *state);

        int (*prepare_writeback_job)(struct drm_writeback_connector *connector,
                                     struct drm_writeback_job *job);
        void (*cleanup_writeback_job)(struct drm_writeback_connector *connector,
                                      struct drm_writeback_job *job);
};

/**
 * drm_connector_helper_add - sets the helper vtable for a connector
 * @connector: DRM connector
 * @funcs: helper vtable to set for @connector
 */
static inline void drm_connector_helper_add(struct drm_connector *connector,
                                            const struct drm_connector_helper_funcs *funcs)
{
        connector->helper_private = funcs;
}

/**
 * struct drm_plane_helper_funcs - helper operations for planes
 *
 * These functions are used by the atomic helpers and by the transitional plane
 * helpers.
 */
struct drm_plane_helper_funcs {
        /**
         * @prepare_fb:
         *
         * This hook is to prepare a framebuffer for scanout by e.g. pinning
         * its backing storage or relocating it into a contiguous block of
         * VRAM. Other possible preparatory work includes flushing caches.
         *
         * This function must not block for outstanding rendering, since it is
         * called in the context of the atomic IOCTL even for async commits to
         * be able to return any errors to userspace. Instead the recommended
         * way is to fill out the &drm_plane_state.fence of the passed-in
         * &drm_plane_state. If the driver doesn't support native fences then
         * equivalent functionality should be implemented through private
         * members in the plane structure.
         *
         * Drivers which always have their buffers pinned should use
         * drm_gem_fb_prepare_fb() for this hook.
         *
         * The helpers will call @cleanup_fb with matching arguments for every
         * successful call to this hook.
         *
         * This callback is used by the atomic modeset helpers and by the
         * transitional plane helpers, but it is optional.
         *
         * RETURNS:
         *
         * 0 on success or one of the following negative error codes allowed by
         * the &drm_mode_config_funcs.atomic_commit vfunc. When using helpers
         * this callback is the only one which can fail an atomic commit,
         * everything else must complete successfully.
         */
        int (*prepare_fb)(struct drm_plane *plane,
                          struct drm_plane_state *new_state);
        /**
         * @cleanup_fb:
         *
         * This hook is called to clean up any resources allocated for the given
         * framebuffer and plane configuration in @prepare_fb.
         *
         * This callback is used by the atomic modeset helpers and by the
         * transitional plane helpers, but it is optional.
         */
        void (*cleanup_fb)(struct drm_plane *plane,
                           struct drm_plane_state *old_state);

        /**
         * @atomic_check:
         *
         * Drivers should check plane specific constraints in this hook.
         *
         * When using drm_atomic_helper_check_planes() plane's @atomic_check
         * hooks are called before the ones for CRTCs, which allows drivers to
         * request shared resources that the CRTC controls here. For more
         * complicated dependencies the driver can call the provided check helpers
         * multiple times until the computed state has a final configuration and
         * everything has been checked.
         *
         * This function is also allowed to inspect any other object's state and
         * can add more state objects to the atomic commit if needed. Care must
         * be taken though to ensure that state check and compute functions for
         * these added states are all called, and derived state in other objects
         * all updated. Again the recommendation is to just call check helpers
         * until a maximal configuration is reached.
         *
         * This callback is used by the atomic modeset helpers and by the
         * transitional plane helpers, but it is optional.
         *
         * NOTE:
         *
         * This function is called in the check phase of an atomic update. The
         * driver is not allowed to change anything outside of the free-standing
         * state objects passed-in or assembled in the overall &drm_atomic_state
         * update tracking structure.
         *
         * RETURNS:
         *
         * 0 on success, -EINVAL if the state or the transition can't be
         * supported, -ENOMEM on memory allocation failure and -EDEADLK if an
         * attempt to obtain another state object ran into a &drm_modeset_lock
         * deadlock.
         */
        int (*atomic_check)(struct drm_plane *plane,
                            struct drm_plane_state *state);

        /**
         * @atomic_update:
         *
         * Drivers should use this function to update the plane state.  This
         * hook is called in-between the &drm_crtc_helper_funcs.atomic_begin and
         * drm_crtc_helper_funcs.atomic_flush callbacks.
         *
         * Note that the power state of the display pipe when this function is
         * called depends upon the exact helpers and calling sequence the driver
         * has picked. See drm_atomic_helper_commit_planes() for a discussion of
         * the tradeoffs and variants of plane commit helpers.
         *
         * This callback is used by the atomic modeset helpers and by the
         * transitional plane helpers, but it is optional.
         */
        void (*atomic_update)(struct drm_plane *plane,
                              struct drm_plane_state *old_state);
        /**
         * @atomic_disable:
         *
         * Drivers should use this function to unconditionally disable a plane.
         * This hook is called in-between the
         * &drm_crtc_helper_funcs.atomic_begin and
         * drm_crtc_helper_funcs.atomic_flush callbacks. It is an alternative to
         * @atomic_update, which will be called for disabling planes, too, if
         * the @atomic_disable hook isn't implemented.
         *
         * This hook is also useful to disable planes in preparation of a modeset,
         * by calling drm_atomic_helper_disable_planes_on_crtc() from the
         * &drm_crtc_helper_funcs.disable hook.
         *
         * Note that the power state of the display pipe when this function is
         * called depends upon the exact helpers and calling sequence the driver
         * has picked. See drm_atomic_helper_commit_planes() for a discussion of
         * the tradeoffs and variants of plane commit helpers.
         *
         * This callback is used by the atomic modeset helpers and by the
         * transitional plane helpers, but it is optional.
         */
        void (*atomic_disable)(struct drm_plane *plane,
                               struct drm_plane_state *old_state);

        /**
         * @atomic_async_check:
         *
         * Drivers should set this function pointer to check if the plane state
         * can be updated in a async fashion. Here async means "not vblank
         * synchronized".
         *
         * This hook is called by drm_atomic_async_check() to establish if a
         * given update can be committed asynchronously, that is, if it can
         * jump ahead of the state currently queued for update.
         *
         * RETURNS:
         *
         * Return 0 on success and any error returned indicates that the update
         * can not be applied in asynchronous manner.
         */
        int (*atomic_async_check)(struct drm_plane *plane,
                                  struct drm_plane_state *state);

        /**
         * @atomic_async_update:
         *
         * Drivers should set this function pointer to perform asynchronous
         * updates of planes, that is, jump ahead of the currently queued
         * state and update the plane. Here async means "not vblank
         * synchronized".
         *
         * This hook is called by drm_atomic_helper_async_commit().
         *
         * An async update will happen on legacy cursor updates. An async
         * update won't happen if there is an outstanding commit modifying
         * the same plane.
         *
         * Note that unlike &drm_plane_helper_funcs.atomic_update this hook
         * takes the new &drm_plane_state as parameter. When doing async_update
         * drivers shouldn't replace the &drm_plane_state but update the
         * current one with the new plane configurations in the new
         * plane_state.
         *
         * Drivers should also swap the framebuffers between current plane
         * state (&drm_plane.state) and new_state.
         * This is required since cleanup for async commits is performed on
         * the new state, rather than old state like for traditional commits.
         * Since we want to give up the reference on the current (old) fb
         * instead of our brand new one, swap them in the driver during the
         * async commit.
         *
         * FIXME:
         *  - It only works for single plane updates
         *  - Async Pageflips are not supported yet
         *  - Some hw might still scan out the old buffer until the next
         *    vblank, however we let go of the fb references as soon as
         *    we run this hook. For now drivers must implement their own workers
         *    for deferring if needed, until a common solution is created.
         */
        void (*atomic_async_update)(struct drm_plane *plane,
                                    struct drm_plane_state *new_state);
};

/**
 * drm_plane_helper_add - sets the helper vtable for a plane
 * @plane: DRM plane
 * @funcs: helper vtable to set for @plane
 */
static inline void drm_plane_helper_add(struct drm_plane *plane,
                                        const struct drm_plane_helper_funcs *funcs)
{
        plane->helper_private = funcs;
}

/**
 * struct drm_mode_config_helper_funcs - global modeset helper operations
 *
 * These helper functions are used by the atomic helpers.
 */
struct drm_mode_config_helper_funcs {
        /**
         * @atomic_commit_tail:
         *
         * This hook is used by the default atomic_commit() hook implemented in
         * drm_atomic_helper_commit() together with the nonblocking commit
         * helpers (see drm_atomic_helper_setup_commit() for a starting point)
         * to implement blocking and nonblocking commits easily. It is not used
         * by the atomic helpers
         *
         * This function is called when the new atomic state has already been
         * swapped into the various state pointers. The passed in state
         * therefore contains copies of the old/previous state. This hook should
         * commit the new state into hardware. Note that the helpers have
         * already waited for preceeding atomic commits and fences, but drivers
         * can add more waiting calls at the start of their implementation, e.g.
         * to wait for driver-internal request for implicit syncing, before
         * starting to commit the update to the hardware.
         *
         * After the atomic update is committed to the hardware this hook needs
         * to call drm_atomic_helper_commit_hw_done(). Then wait for the upate
         * to be executed by the hardware, for example using
         * drm_atomic_helper_wait_for_vblanks() or
         * drm_atomic_helper_wait_for_flip_done(), and then clean up the old
         * framebuffers using drm_atomic_helper_cleanup_planes().
         *
         * When disabling a CRTC this hook _must_ stall for the commit to
         * complete. Vblank waits don't work on disabled CRTC, hence the core
         * can't take care of this. And it also can't rely on the vblank event,
         * since that can be signalled already when the screen shows black,
         * which can happen much earlier than the last hardware access needed to
         * shut off the display pipeline completely.
         *
         * This hook is optional, the default implementation is
         * drm_atomic_helper_commit_tail().
         */
        void (*atomic_commit_tail)(struct drm_atomic_state *state);
};

#endif