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 /*
  * 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 object passed-in.
      *
      * 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_atomic_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_atomic_state *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_atomic_state *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.
      *
      * This function is optional.
      */
     void (*atomic_enable)(struct drm_crtc *crtc,
                   struct drm_atomic_state *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.
      *
      * This function is optional.
      */
     void (*atomic_disable)(struct drm_crtc *crtc,
                    struct drm_atomic_state *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 drive 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.
      *
      * Note that the caller function will automatically add standard VESA
      * DMT modes up to 1024x768 if the .get_modes() helper operation returns
      * no mode and if the connector status is connector_status_connected or
      * connector_status_unknown. There is no need to call
      * drm_add_modes_noedid() manually in that case.
      *
      * 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);
 
     /**
      * @mode_valid_ctx:
      *
      * 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, and is the atomic version of
      * &drm_connector_helper_funcs.mode_valid.
      *
      * To allow for accessing the atomic state of modesetting objects, 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 @ctx. This allows for taking additional
      * locks as required.
      *
      * Even though additional locks may be acquired, this callback is
      * still expected not to take any constraints into account which would
      * be influenced by the currently set display state - such constraints
      * should be handled in the driver's atomic check. For example, if a
      * connector shares display bandwidth with other connectors then it
      * would be ok to validate the minimum bandwidth requirement of a mode
      * against the maximum possible bandwidth of the connector. But it
      * wouldn't be ok to take the current bandwidth usage of other
      * connectors into account, as this would change depending on the
      * display state.
      *
      * Returns:
      * 0 if &drm_connector_helper_funcs.mode_valid_ctx succeeded and wrote
      * the &enum drm_mode_status value to @status, or a negative error
      * code otherwise.
      *
      */
     int (*mode_valid_ctx)(struct drm_connector *connector,
                   struct drm_display_mode *mode,
                   struct drm_modeset_acquire_ctx *ctx,
                   enum drm_mode_status *status);
 
     /**
      * @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
      * &drm_atomic_state update tracking structure passed in.
      *
      * 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_atomic_state *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 the new connector state,
      * 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_atomic_state *state);
 
     /**
      * @prepare_writeback_job:
      *
      * As writeback jobs contain a framebuffer, drivers may need to
      * prepare and clean them up the same way they can prepare and
      * clean up framebuffers for planes. This optional connector operation
      * is used to support the preparation of writeback jobs. The job
      * prepare operation is called from drm_atomic_helper_prepare_planes()
      * for struct &drm_writeback_connector connectors only.
      *
      * This operation is optional.
      *
      * This callback is used by the atomic modeset helpers.
      */
     int (*prepare_writeback_job)(struct drm_writeback_connector *connector,
                      struct drm_writeback_job *job);
     /**
      * @cleanup_writeback_job:
      *
      * This optional connector operation is used to support the
      * cleanup of writeback jobs. The job cleanup operation is called
      * from the existing drm_writeback_cleanup_job() function, invoked
      * both when destroying the job as part of an aborted commit, or when
      * the job completes.
      *
      * This operation is optional.
      *
      * This callback is used by the atomic modeset helpers.
      */
     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.
      *
      * For GEM drivers who neither have a @prepare_fb nor @cleanup_fb hook
      * set drm_gem_plane_helper_prepare_fb() is called automatically to
      * implement this. Other drivers which need additional plane processing
      * can call drm_gem_plane_helper_prepare_fb() from their @prepare_fb
      * 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
      * &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_atomic_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_atomic_state *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_atomic_state *state);
 
     /**
      * @atomic_async_check:
      *
      * Drivers should set this function pointer to check if the plane's
      * atomic 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_atomic_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.
      *
      * 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_atomic_state *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 update
      * 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);
 
     /**
      * @atomic_commit_setup:
      *
      * This hook is used by the default atomic_commit() hook implemented in
      * drm_atomic_helper_commit() together with the nonblocking helpers (see
      * drm_atomic_helper_setup_commit()) to extend the DRM commit setup. It
      * is not used by the atomic helpers.
      *
      * This function is called at the end of
      * drm_atomic_helper_setup_commit(), so once the commit has been
      * properly setup across the generic DRM object states. It allows
      * drivers to do some additional commit tracking that isn't related to a
      * CRTC, plane or connector, tracked in a &drm_private_obj structure.
      *
      * Note that the documentation of &drm_private_obj has more details on
      * how one should implement this.
      *
      * This hook is optional.
      */
     int (*atomic_commit_setup)(struct drm_atomic_state *state);
 };
 
 #endif

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