text: /*
   * Copyright (c) 2016 Intel Corporation
   *
   * Permission to use, copy, modify, distribute, and sell this software and its
   * documentation for any purpose is hereby granted without fee, provided that
   * the above copyright notice appear in all copies and that both that copyright
   * notice and this permission notice appear in supporting documentation, and
   * that the name of the copyright holders not be used in advertising or
   * publicity pertaining to distribution of the software without specific,
   * written prior permission.  The copyright holders make no representations
   * about the suitability of this software for any purpose.  It is provided "as
   * is" without express or implied warranty.
   *
   * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
   * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
   * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
   * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
   * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
   * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
   * OF THIS SOFTWARE.
   */
  
  #ifndef __DRM_BRIDGE_H__
  #define __DRM_BRIDGE_H__
  
  #include <linux/ctype.h>
  #include <linux/list.h>
  #include <linux/mutex.h>
  
  #include <drm/drm_atomic.h>
  #include <drm/drm_encoder.h>
  #include <drm/drm_mode_object.h>
  #include <drm/drm_modes.h>
  
  struct drm_bridge;
  struct drm_bridge_timings;
  struct drm_connector;
  struct drm_display_info;
  struct drm_panel;
  struct edid;
  struct i2c_adapter;
  
  /**
   * enum drm_bridge_attach_flags - Flags for &drm_bridge_funcs.attach
   */
  enum drm_bridge_attach_flags {
  	/**
  	 * @DRM_BRIDGE_ATTACH_NO_CONNECTOR: When this flag is set the bridge
  	 * shall not create a drm_connector.
  	 */
  	DRM_BRIDGE_ATTACH_NO_CONNECTOR = BIT(0),
  };
  
  /**
   * struct drm_bridge_funcs - drm_bridge control functions
   */
  struct drm_bridge_funcs {
  	/**
  	 * @attach:
  	 *
  	 * This callback is invoked whenever our bridge is being attached to a
  	 * &drm_encoder. The flags argument tunes the behaviour of the attach
  	 * operation (see DRM_BRIDGE_ATTACH_*).
  	 *
  	 * The @attach callback is optional.
  	 *
  	 * RETURNS:
  	 *
  	 * Zero on success, error code on failure.
  	 */
  	int (*attach)(struct drm_bridge *bridge,
  		      enum drm_bridge_attach_flags flags);
  
  	/**
  	 * @detach:
  	 *
  	 * This callback is invoked whenever our bridge is being detached from a
  	 * &drm_encoder.
  	 *
  	 * The @detach callback is optional.
  	 */
  	void (*detach)(struct drm_bridge *bridge);
  
  	/**
  	 * @mode_valid:
  	 *
  	 * This callback is used to check if a specific mode is valid in this
  	 * bridge. This should be implemented if the bridge has some sort of
  	 * restriction in the modes it can display. For example, a given bridge
  	 * 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().
  	 *
  	 * The @mode_valid callback 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.
  	 *
  	 * RETURNS:
  	 *
  	 * drm_mode_status Enum
  	 */
  	enum drm_mode_status (*mode_valid)(struct drm_bridge *bridge,
  					   const struct drm_display_info *info,
  					   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 the next
  	 * &drm_bridge. The parameter adjusted_mode is the input mode the bridge
  	 * 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 is the only hook that allows a bridge to reject a modeset. If
  	 * this function passes all other callbacks must succeed for this
  	 * configuration.
  	 *
  	 * The mode_fixup callback is optional. &drm_bridge_funcs.mode_fixup()
  	 * is not called when &drm_bridge_funcs.atomic_check() is implemented,
  	 * so only one of them should be provided.
  	 *
  	 * 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). Drivers MUST
  	 * NOT touch any persistent state (hardware or software) or data
  	 * structures except the passed in @state parameter.
  	 *
  	 * 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 bridge 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_bridge *bridge,
  			   const struct drm_display_mode *mode,
  			   struct drm_display_mode *adjusted_mode);
  	/**
  	 * @disable:
  	 *
  	 * This callback should disable the bridge. It is called right before
  	 * the preceding element in the display pipe is disabled. If the
  	 * preceding element is a bridge this means it's called before that
  	 * bridge's @disable vfunc. If the preceding element is a &drm_encoder
  	 * it's called right before the &drm_encoder_helper_funcs.disable,
  	 * &drm_encoder_helper_funcs.prepare or &drm_encoder_helper_funcs.dpms
  	 * hook.
  	 *
  	 * The bridge can assume that the display pipe (i.e. clocks and timing
  	 * signals) feeding it is still running when this callback is called.
  	 *
  	 * The @disable callback is optional.
  	 *
  	 * NOTE:
  	 *
  	 * This is deprecated, do not use!
  	 * New drivers shall use &drm_bridge_funcs.atomic_disable.
  	 */
  	void (*disable)(struct drm_bridge *bridge);
  
  	/**
  	 * @post_disable:
  	 *
  	 * This callback should disable the bridge. It is called right after the
  	 * preceding element in the display pipe is disabled. If the preceding
  	 * element is a bridge this means it's called after that bridge's
  	 * @post_disable function. If the preceding element is a &drm_encoder
  	 * it's called right after the encoder's
  	 * &drm_encoder_helper_funcs.disable, &drm_encoder_helper_funcs.prepare
  	 * or &drm_encoder_helper_funcs.dpms hook.
  	 *
  	 * The bridge must assume that the display pipe (i.e. clocks and timing
  	 * singals) feeding it is no longer running when this callback is
  	 * called.
  	 *
  	 * The @post_disable callback is optional.
  	 *
  	 * NOTE:
  	 *
  	 * This is deprecated, do not use!
  	 * New drivers shall use &drm_bridge_funcs.atomic_post_disable.
  	 */
  	void (*post_disable)(struct drm_bridge *bridge);
  
  	/**
  	 * @mode_set:
  	 *
  	 * This callback should set the given mode on the bridge. It is called
  	 * after the @mode_set callback for the preceding element in the display
  	 * pipeline has been called already. If the bridge is the first element
  	 * then this would be &drm_encoder_helper_funcs.mode_set. The display
  	 * pipe (i.e.  clocks and timing signals) is off when this function is
  	 * called.
  	 *
  	 * The adjusted_mode parameter is the mode output by the CRTC for the
  	 * first bridge in the chain. It can be different from the mode
  	 * parameter that contains the desired mode for the connector at the end
  	 * of the bridges chain, for instance when the first bridge in the chain
  	 * performs scaling. The adjusted mode is mostly useful for the first
  	 * bridge in the chain and is likely irrelevant for the other bridges.
  	 *
  	 * For atomic drivers the adjusted_mode is the mode stored in
  	 * &drm_crtc_state.adjusted_mode.
  	 *
  	 * NOTE:
  	 *
  	 * This is deprecated, do not use!
  	 * New drivers shall set their mode in the
  	 * &drm_bridge_funcs.atomic_enable operation.
  	 */
  	void (*mode_set)(struct drm_bridge *bridge,
  			 const struct drm_display_mode *mode,
  			 const struct drm_display_mode *adjusted_mode);
  	/**
  	 * @pre_enable:
  	 *
  	 * This callback should enable the bridge. It is called right before
  	 * the preceding element in the display pipe is enabled. If the
  	 * preceding element is a bridge this means it's called before that
  	 * bridge's @pre_enable function. If the preceding element is a
  	 * &drm_encoder it's called right before the encoder's
  	 * &drm_encoder_helper_funcs.enable, &drm_encoder_helper_funcs.commit or
  	 * &drm_encoder_helper_funcs.dpms hook.
  	 *
  	 * The display pipe (i.e. clocks and timing signals) feeding this bridge
  	 * will not yet be running when this callback is called. The bridge must
  	 * not enable the display link feeding the next bridge in the chain (if
  	 * there is one) when this callback is called.
  	 *
  	 * The @pre_enable callback is optional.
  	 *
  	 * NOTE:
  	 *
  	 * This is deprecated, do not use!
  	 * New drivers shall use &drm_bridge_funcs.atomic_pre_enable.
  	 */
  	void (*pre_enable)(struct drm_bridge *bridge);
  
  	/**
  	 * @enable:
  	 *
  	 * This callback should enable the bridge. It is called right after
  	 * the preceding element in the display pipe is enabled. If the
  	 * preceding element is a bridge this means it's called after that
  	 * bridge's @enable function. If the preceding element is a
  	 * &drm_encoder it's called right after the encoder's
  	 * &drm_encoder_helper_funcs.enable, &drm_encoder_helper_funcs.commit or
  	 * &drm_encoder_helper_funcs.dpms hook.
  	 *
  	 * The bridge can assume that the display pipe (i.e. clocks and timing
  	 * signals) feeding it is running when this callback is called. This
  	 * callback must enable the display link feeding the next bridge in the
  	 * chain if there is one.
  	 *
  	 * The @enable callback is optional.
  	 *
  	 * NOTE:
  	 *
  	 * This is deprecated, do not use!
  	 * New drivers shall use &drm_bridge_funcs.atomic_enable.
  	 */
  	void (*enable)(struct drm_bridge *bridge);
  
  	/**
  	 * @atomic_pre_enable:
  	 *
  	 * This callback should enable the bridge. It is called right before
  	 * the preceding element in the display pipe is enabled. If the
  	 * preceding element is a bridge this means it's called before that
  	 * bridge's @atomic_pre_enable or @pre_enable function. If the preceding
  	 * element is a &drm_encoder it's called right before the encoder's
  	 * &drm_encoder_helper_funcs.atomic_enable hook.
  	 *
  	 * The display pipe (i.e. clocks and timing signals) feeding this bridge
  	 * will not yet be running when this callback is called. The bridge must
  	 * not enable the display link feeding the next bridge in the chain (if
  	 * there is one) when this callback is called.
  	 *
  	 * Note that this function will only be invoked in the context of an
  	 * atomic commit. It will not be invoked from
  	 * &drm_bridge_chain_pre_enable. It would be prudent to also provide an
  	 * implementation of @pre_enable if you are expecting driver calls into
  	 * &drm_bridge_chain_pre_enable.
  	 *
  	 * The @atomic_pre_enable callback is optional.
  	 */
  	void (*atomic_pre_enable)(struct drm_bridge *bridge,
  				  struct drm_bridge_state *old_bridge_state);
  
  	/**
  	 * @atomic_enable:
  	 *
  	 * This callback should enable the bridge. It is called right after
  	 * the preceding element in the display pipe is enabled. If the
  	 * preceding element is a bridge this means it's called after that
  	 * bridge's @atomic_enable or @enable function. If the preceding element
  	 * is a &drm_encoder it's called right after the encoder's
  	 * &drm_encoder_helper_funcs.atomic_enable hook.
  	 *
  	 * The bridge can assume that the display pipe (i.e. clocks and timing
  	 * signals) feeding it is running when this callback is called. This
  	 * callback must enable the display link feeding the next bridge in the
  	 * chain if there is one.
  	 *
  	 * Note that this function will only be invoked in the context of an
  	 * atomic commit. It will not be invoked from &drm_bridge_chain_enable.
  	 * It would be prudent to also provide an implementation of @enable if
  	 * you are expecting driver calls into &drm_bridge_chain_enable.
  	 *
  	 * The @atomic_enable callback is optional.
  	 */
  	void (*atomic_enable)(struct drm_bridge *bridge,
  			      struct drm_bridge_state *old_bridge_state);
  	/**
  	 * @atomic_disable:
  	 *
  	 * This callback should disable the bridge. It is called right before
  	 * the preceding element in the display pipe is disabled. If the
  	 * preceding element is a bridge this means it's called before that
  	 * bridge's @atomic_disable or @disable vfunc. If the preceding element
  	 * is a &drm_encoder it's called right before the
  	 * &drm_encoder_helper_funcs.atomic_disable hook.
  	 *
  	 * The bridge can assume that the display pipe (i.e. clocks and timing
  	 * signals) feeding it is still running when this callback is called.
  	 *
  	 * Note that this function will only be invoked in the context of an
  	 * atomic commit. It will not be invoked from
  	 * &drm_bridge_chain_disable. It would be prudent to also provide an
  	 * implementation of @disable if you are expecting driver calls into
  	 * &drm_bridge_chain_disable.
  	 *
  	 * The @atomic_disable callback is optional.
  	 */
  	void (*atomic_disable)(struct drm_bridge *bridge,
  			       struct drm_bridge_state *old_bridge_state);
  
  	/**
  	 * @atomic_post_disable:
  	 *
  	 * This callback should disable the bridge. It is called right after the
  	 * preceding element in the display pipe is disabled. If the preceding
  	 * element is a bridge this means it's called after that bridge's
  	 * @atomic_post_disable or @post_disable function. If the preceding
  	 * element is a &drm_encoder it's called right after the encoder's
  	 * &drm_encoder_helper_funcs.atomic_disable hook.
  	 *
  	 * The bridge must assume that the display pipe (i.e. clocks and timing
  	 * signals) feeding it is no longer running when this callback is
  	 * called.
  	 *
  	 * Note that this function will only be invoked in the context of an
  	 * atomic commit. It will not be invoked from
  	 * &drm_bridge_chain_post_disable.
  	 * It would be prudent to also provide an implementation of
  	 * @post_disable if you are expecting driver calls into
  	 * &drm_bridge_chain_post_disable.
  	 *
  	 * The @atomic_post_disable callback is optional.
  	 */
  	void (*atomic_post_disable)(struct drm_bridge *bridge,
  				    struct drm_bridge_state *old_bridge_state);
  
  	/**
  	 * @atomic_duplicate_state:
  	 *
  	 * Duplicate the current bridge state object (which is guaranteed to be
  	 * non-NULL).
  	 *
  	 * The atomic_duplicate_state hook is mandatory if the bridge
  	 * implements any of the atomic hooks, and should be left unassigned
  	 * otherwise. For bridges that don't subclass &drm_bridge_state, the
  	 * drm_atomic_helper_bridge_duplicate_state() helper function shall be
  	 * used to implement this hook.
  	 *
  	 * RETURNS:
  	 * A valid drm_bridge_state object or NULL if the allocation fails.
  	 */
  	struct drm_bridge_state *(*atomic_duplicate_state)(struct drm_bridge *bridge);
  
  	/**
  	 * @atomic_destroy_state:
  	 *
  	 * Destroy a bridge state object previously allocated by
  	 * &drm_bridge_funcs.atomic_duplicate_state().
  	 *
  	 * The atomic_destroy_state hook is mandatory if the bridge implements
  	 * any of the atomic hooks, and should be left unassigned otherwise.
  	 * For bridges that don't subclass &drm_bridge_state, the
  	 * drm_atomic_helper_bridge_destroy_state() helper function shall be
  	 * used to implement this hook.
  	 */
  	void (*atomic_destroy_state)(struct drm_bridge *bridge,
  				     struct drm_bridge_state *state);
  
  	/**
  	 * @atomic_get_output_bus_fmts:
  	 *
  	 * Return the supported bus formats on the output end of a bridge.
  	 * The returned array must be allocated with kmalloc() and will be
  	 * freed by the caller. If the allocation fails, NULL should be
  	 * returned. num_output_fmts must be set to the returned array size.
  	 * Formats listed in the returned array should be listed in decreasing
  	 * preference order (the core will try all formats until it finds one
  	 * that works).
  	 *
  	 * This method is only called on the last element of the bridge chain
  	 * as part of the bus format negotiation process that happens in
  	 * &drm_atomic_bridge_chain_select_bus_fmts().
  	 * This method is optional. When not implemented, the core will
  	 * fall back to &drm_connector.display_info.bus_formats[0] if
  	 * &drm_connector.display_info.num_bus_formats > 0,
  	 * or to MEDIA_BUS_FMT_FIXED otherwise.
  	 */
  	u32 *(*atomic_get_output_bus_fmts)(struct drm_bridge *bridge,
  					   struct drm_bridge_state *bridge_state,
  					   struct drm_crtc_state *crtc_state,
  					   struct drm_connector_state *conn_state,
  					   unsigned int *num_output_fmts);
  
  	/**
  	 * @atomic_get_input_bus_fmts:
  	 *
  	 * Return the supported bus formats on the input end of a bridge for
  	 * a specific output bus format.
  	 *
  	 * The returned array must be allocated with kmalloc() and will be
  	 * freed by the caller. If the allocation fails, NULL should be
  	 * returned. num_output_fmts must be set to the returned array size.
  	 * Formats listed in the returned array should be listed in decreasing
  	 * preference order (the core will try all formats until it finds one
  	 * that works). When the format is not supported NULL should be
  	 * returned and num_output_fmts should be set to 0.
  	 *
  	 * This method is called on all elements of the bridge chain as part of
  	 * the bus format negotiation process that happens in
  	 * drm_atomic_bridge_chain_select_bus_fmts().
  	 * This method is optional. When not implemented, the core will bypass
  	 * bus format negotiation on this element of the bridge without
  	 * failing, and the previous element in the chain will be passed
  	 * MEDIA_BUS_FMT_FIXED as its output bus format.
  	 *
  	 * Bridge drivers that need to support being linked to bridges that are
  	 * not supporting bus format negotiation should handle the
  	 * output_fmt == MEDIA_BUS_FMT_FIXED case appropriately, by selecting a
  	 * sensible default value or extracting this information from somewhere
  	 * else (FW property, &drm_display_mode, &drm_display_info, ...)
  	 *
  	 * Note: Even if input format selection on the first bridge has no
  	 * impact on the negotiation process (bus format negotiation stops once
  	 * we reach the first element of the chain), drivers are expected to
  	 * return accurate input formats as the input format may be used to
  	 * configure the CRTC output appropriately.
  	 */
  	u32 *(*atomic_get_input_bus_fmts)(struct drm_bridge *bridge,
  					  struct drm_bridge_state *bridge_state,
  					  struct drm_crtc_state *crtc_state,
  					  struct drm_connector_state *conn_state,
  					  u32 output_fmt,
  					  unsigned int *num_input_fmts);
  
  	/**
  	 * @atomic_check:
  	 *
  	 * This method is responsible for checking bridge state correctness.
  	 * It can also check the state of the surrounding components in chain
  	 * to make sure the whole pipeline can work properly.
  	 *
  	 * &drm_bridge_funcs.atomic_check() hooks are called in reverse
  	 * order (from the last to the first bridge).
  	 *
  	 * This method is optional. &drm_bridge_funcs.mode_fixup() is not
  	 * called when &drm_bridge_funcs.atomic_check() is implemented, so only
  	 * one of them should be provided.
  	 *
  	 * If drivers need to tweak &drm_bridge_state.input_bus_cfg.flags or
  	 * &drm_bridge_state.output_bus_cfg.flags it should happen in
  	 * this function. By default the &drm_bridge_state.output_bus_cfg.flags
  	 * field is set to the next bridge
  	 * &drm_bridge_state.input_bus_cfg.flags value or
  	 * &drm_connector.display_info.bus_flags if the bridge is the last
  	 * element in the chain.
  	 *
  	 * RETURNS:
  	 * zero if the check passed, a negative error code otherwise.
  	 */
  	int (*atomic_check)(struct drm_bridge *bridge,
  			    struct drm_bridge_state *bridge_state,
  			    struct drm_crtc_state *crtc_state,
  			    struct drm_connector_state *conn_state);
  
  	/**
  	 * @atomic_reset:
  	 *
  	 * Reset the bridge to a predefined state (or retrieve its current
  	 * state) and return a &drm_bridge_state object matching this state.
  	 * This function is called at attach time.
  	 *
  	 * The atomic_reset hook is mandatory if the bridge implements any of
  	 * the atomic hooks, and should be left unassigned otherwise. For
  	 * bridges that don't subclass &drm_bridge_state, the
  	 * drm_atomic_helper_bridge_reset() helper function shall be used to
  	 * implement this hook.
  	 *
  	 * Note that the atomic_reset() semantics is not exactly matching the
  	 * reset() semantics found on other components (connector, plane, ...).
  	 *
  	 * 1. The reset operation happens when the bridge is attached, not when
  	 *    drm_mode_config_reset() is called
  	 * 2. It's meant to be used exclusively on bridges that have been
  	 *    converted to the ATOMIC API
  	 *
  	 * RETURNS:
  	 * A valid drm_bridge_state object in case of success, an ERR_PTR()
  	 * giving the reason of the failure otherwise.
  	 */
  	struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);
  
  	/**
  	 * @detect:
  	 *
  	 * Check if anything is attached to the bridge output.
  	 *
  	 * This callback is optional, if not implemented the bridge will be
  	 * considered as always having a component attached to its output.
  	 * Bridges that implement this callback shall set the
  	 * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
  	 *
  	 * RETURNS:
  	 *
  	 * drm_connector_status indicating the bridge output status.
  	 */
  	enum drm_connector_status (*detect)(struct drm_bridge *bridge);
  
  	/**
  	 * @get_modes:
  	 *
  	 * Fill all modes currently valid for the sink into the &drm_connector
  	 * with drm_mode_probed_add().
  	 *
  	 * The @get_modes callback is mostly intended to support non-probeable
  	 * displays such as many fixed panels. Bridges that support reading
  	 * EDID shall leave @get_modes unimplemented and implement the
  	 * &drm_bridge_funcs->get_edid callback instead.
  	 *
  	 * This callback is optional. Bridges that implement it shall set the
  	 * DRM_BRIDGE_OP_MODES flag in their &drm_bridge->ops.
  	 *
  	 * The connector parameter shall be used for the sole purpose of
  	 * filling modes, and shall not be stored internally by bridge drivers
  	 * for future usage.
  	 *
  	 * RETURNS:
  	 *
  	 * The number of modes added by calling drm_mode_probed_add().
  	 */
  	int (*get_modes)(struct drm_bridge *bridge,
  			 struct drm_connector *connector);
  
  	/**
  	 * @get_edid:
  	 *
  	 * Read and parse the EDID data of the connected display.
  	 *
  	 * The @get_edid callback is the preferred way of reporting mode
  	 * information for a display connected to the bridge output. Bridges
  	 * that support reading EDID shall implement this callback and leave
  	 * the @get_modes callback unimplemented.
  	 *
  	 * The caller of this operation shall first verify the output
  	 * connection status and refrain from reading EDID from a disconnected
  	 * output.
  	 *
  	 * This callback is optional. Bridges that implement it shall set the
  	 * DRM_BRIDGE_OP_EDID flag in their &drm_bridge->ops.
  	 *
  	 * The connector parameter shall be used for the sole purpose of EDID
  	 * retrieval and parsing, and shall not be stored internally by bridge
  	 * drivers for future usage.
  	 *
  	 * RETURNS:
  	 *
  	 * An edid structure newly allocated with kmalloc() (or similar) on
  	 * success, or NULL otherwise. The caller is responsible for freeing
  	 * the returned edid structure with kfree().
  	 */
  	struct edid *(*get_edid)(struct drm_bridge *bridge,
  				 struct drm_connector *connector);
  
  	/**
  	 * @hpd_notify:
  	 *
  	 * Notify the bridge of hot plug detection.
  	 *
  	 * This callback is optional, it may be implemented by bridges that
  	 * need to be notified of display connection or disconnection for
  	 * internal reasons. One use case is to reset the internal state of CEC
  	 * controllers for HDMI bridges.
  	 */
  	void (*hpd_notify)(struct drm_bridge *bridge,
  			   enum drm_connector_status status);
  
  	/**
  	 * @hpd_enable:
  	 *
  	 * Enable hot plug detection. From now on the bridge shall call
  	 * drm_bridge_hpd_notify() each time a change is detected in the output
  	 * connection status, until hot plug detection gets disabled with
  	 * @hpd_disable.
  	 *
  	 * This callback is optional and shall only be implemented by bridges
  	 * that support hot-plug notification without polling. Bridges that
  	 * implement it shall also implement the @hpd_disable callback and set
  	 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
  	 */
  	void (*hpd_enable)(struct drm_bridge *bridge);
  
  	/**
  	 * @hpd_disable:
  	 *
  	 * Disable hot plug detection. Once this function returns the bridge
  	 * shall not call drm_bridge_hpd_notify() when a change in the output
  	 * connection status occurs.
  	 *
  	 * This callback is optional and shall only be implemented by bridges
  	 * that support hot-plug notification without polling. Bridges that
  	 * implement it shall also implement the @hpd_enable callback and set
  	 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
  	 */
  	void (*hpd_disable)(struct drm_bridge *bridge);
  };
  
  /**
   * struct drm_bridge_timings - timing information for the bridge
   */
  struct drm_bridge_timings {
  	/**
  	 * @input_bus_flags:
  	 *
  	 * Tells what additional settings for the pixel data on the bus
  	 * this bridge requires (like pixel signal polarity). See also
  	 * &drm_display_info->bus_flags.
  	 */
  	u32 input_bus_flags;
  	/**
  	 * @setup_time_ps:
  	 *
  	 * Defines the time in picoseconds the input data lines must be
  	 * stable before the clock edge.
  	 */
  	u32 setup_time_ps;
  	/**
  	 * @hold_time_ps:
  	 *
  	 * Defines the time in picoseconds taken for the bridge to sample the
  	 * input signal after the clock edge.
  	 */
  	u32 hold_time_ps;
  	/**
  	 * @dual_link:
  	 *
  	 * True if the bus operates in dual-link mode. The exact meaning is
  	 * dependent on the bus type. For LVDS buses, this indicates that even-
  	 * and odd-numbered pixels are received on separate links.
  	 */
  	bool dual_link;
  };
  
  /**
   * enum drm_bridge_ops - Bitmask of operations supported by the bridge
   */
  enum drm_bridge_ops {
  	/**
  	 * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
  	 * its output. Bridges that set this flag shall implement the
  	 * &drm_bridge_funcs->detect callback.
  	 */
  	DRM_BRIDGE_OP_DETECT = BIT(0),
  	/**
  	 * @DRM_BRIDGE_OP_EDID: The bridge can retrieve the EDID of the display
  	 * connected to its output. Bridges that set this flag shall implement
  	 * the &drm_bridge_funcs->get_edid callback.
  	 */
  	DRM_BRIDGE_OP_EDID = BIT(1),
  	/**
  	 * @DRM_BRIDGE_OP_HPD: The bridge can detect hot-plug and hot-unplug
  	 * without requiring polling. Bridges that set this flag shall
  	 * implement the &drm_bridge_funcs->hpd_enable and
  	 * &drm_bridge_funcs->hpd_disable callbacks if they support enabling
  	 * and disabling hot-plug detection dynamically.
  	 */
  	DRM_BRIDGE_OP_HPD = BIT(2),
  	/**
  	 * @DRM_BRIDGE_OP_MODES: The bridge can retrieve the modes supported
  	 * by the display at its output. This does not include reading EDID
  	 * which is separately covered by @DRM_BRIDGE_OP_EDID. Bridges that set
  	 * this flag shall implement the &drm_bridge_funcs->get_modes callback.
  	 */
  	DRM_BRIDGE_OP_MODES = BIT(3),
  };
  
  /**
   * struct drm_bridge - central DRM bridge control structure
   */
  struct drm_bridge {
  	/** @base: inherit from &drm_private_object */
  	struct drm_private_obj base;
  	/** @dev: DRM device this bridge belongs to */
  	struct drm_device *dev;
  	/** @encoder: encoder to which this bridge is connected */
  	struct drm_encoder *encoder;
  	/** @chain_node: used to form a bridge chain */
  	struct list_head chain_node;
  #ifdef CONFIG_OF
  	/** @of_node: device node pointer to the bridge */
  	struct device_node *of_node;
  #endif
  	/** @list: to keep track of all added bridges */
  	struct list_head list;
  	/**
  	 * @timings:
  	 *
  	 * the timing specification for the bridge, if any (may be NULL)
  	 */
  	const struct drm_bridge_timings *timings;
  	/** @funcs: control functions */
  	const struct drm_bridge_funcs *funcs;
  	/** @driver_private: pointer to the bridge driver's internal context */
  	void *driver_private;
  	/** @ops: bitmask of operations supported by the bridge */
  	enum drm_bridge_ops ops;
  	/**
  	 * @type: Type of the connection at the bridge output
  	 * (DRM_MODE_CONNECTOR_*). For bridges at the end of this chain this
  	 * identifies the type of connected display.
  	 */
  	int type;
  	/**
  	 * @interlace_allowed: Indicate that the bridge can handle interlaced
  	 * modes.
  	 */
  	bool interlace_allowed;
  	/**
  	 * @ddc: Associated I2C adapter for DDC access, if any.
  	 */
  	struct i2c_adapter *ddc;
  	/** private: */
  	/**
  	 * @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
  	 */
  	struct mutex hpd_mutex;
  	/**
  	 * @hpd_cb: Hot plug detection callback, registered with
  	 * drm_bridge_hpd_enable().
  	 */
  	void (*hpd_cb)(void *data, enum drm_connector_status status);
  	/**
  	 * @hpd_data: Private data passed to the Hot plug detection callback
  	 * @hpd_cb.
  	 */
  	void *hpd_data;
  };
  
  static inline struct drm_bridge *
  drm_priv_to_bridge(struct drm_private_obj *priv)
  {
  	return container_of(priv, struct drm_bridge, base);
  }
  
  void drm_bridge_add(struct drm_bridge *bridge);
  void drm_bridge_remove(struct drm_bridge *bridge);
  int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
  		      struct drm_bridge *previous,
  		      enum drm_bridge_attach_flags flags);
  
  #ifdef CONFIG_OF
  struct drm_bridge *of_drm_find_bridge(struct device_node *np);
  #else
  static inline struct drm_bridge *of_drm_find_bridge(struct device_node *np)
  {
  	return NULL;
  }
  #endif
  
  /**
   * drm_bridge_get_next_bridge() - Get the next bridge in the chain
   * @bridge: bridge object
   *
   * RETURNS:
   * the next bridge in the chain after @bridge, or NULL if @bridge is the last.
   */
  static inline struct drm_bridge *
  drm_bridge_get_next_bridge(struct drm_bridge *bridge)
  {
  	if (list_is_last(&bridge->chain_node, &bridge->encoder->bridge_chain))
  		return NULL;
  
  	return list_next_entry(bridge, chain_node);
  }
  
  /**
   * drm_bridge_get_prev_bridge() - Get the previous bridge in the chain
   * @bridge: bridge object
   *
   * RETURNS:
   * the previous bridge in the chain, or NULL if @bridge is the first.
   */
  static inline struct drm_bridge *
  drm_bridge_get_prev_bridge(struct drm_bridge *bridge)
  {
  	if (list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain))
  		return NULL;
  
  	return list_prev_entry(bridge, chain_node);
  }
  
  /**
   * drm_bridge_chain_get_first_bridge() - Get the first bridge in the chain
   * @encoder: encoder object
   *
   * RETURNS:
   * the first bridge in the chain, or NULL if @encoder has no bridge attached
   * to it.
   */
  static inline struct drm_bridge *
  drm_bridge_chain_get_first_bridge(struct drm_encoder *encoder)
  {
  	return list_first_entry_or_null(&encoder->bridge_chain,
  					struct drm_bridge, chain_node);
  }
  
  /**
   * drm_for_each_bridge_in_chain() - Iterate over all bridges present in a chain
   * @encoder: the encoder to iterate bridges on
   * @bridge: a bridge pointer updated to point to the current bridge at each
   *	    iteration
   *
   * Iterate over all bridges present in the bridge chain attached to @encoder.
   */
  #define drm_for_each_bridge_in_chain(encoder, bridge)			\
  	list_for_each_entry(bridge, &(encoder)->bridge_chain, chain_node)
  
  bool drm_bridge_chain_mode_fixup(struct drm_bridge *bridge,
  				 const struct drm_display_mode *mode,
  				 struct drm_display_mode *adjusted_mode);
  enum drm_mode_status
  drm_bridge_chain_mode_valid(struct drm_bridge *bridge,
  			    const struct drm_display_info *info,
  			    const struct drm_display_mode *mode);
  void drm_bridge_chain_disable(struct drm_bridge *bridge);
  void drm_bridge_chain_post_disable(struct drm_bridge *bridge);
  void drm_bridge_chain_mode_set(struct drm_bridge *bridge,
  			       const struct drm_display_mode *mode,
  			       const struct drm_display_mode *adjusted_mode);
  void drm_bridge_chain_pre_enable(struct drm_bridge *bridge);
  void drm_bridge_chain_enable(struct drm_bridge *bridge);
  
  int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
  				  struct drm_crtc_state *crtc_state,
  				  struct drm_connector_state *conn_state);
  void drm_atomic_bridge_chain_disable(struct drm_bridge *bridge,
  				     struct drm_atomic_state *state);
  void drm_atomic_bridge_chain_post_disable(struct drm_bridge *bridge,
  					  struct drm_atomic_state *state);
  void drm_atomic_bridge_chain_pre_enable(struct drm_bridge *bridge,
  					struct drm_atomic_state *state);
  void drm_atomic_bridge_chain_enable(struct drm_bridge *bridge,
  				    struct drm_atomic_state *state);
  
  u32 *
  drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
  					struct drm_bridge_state *bridge_state,
  					struct drm_crtc_state *crtc_state,
  					struct drm_connector_state *conn_state,
  					u32 output_fmt,
  					unsigned int *num_input_fmts);
  
  enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge);
  int drm_bridge_get_modes(struct drm_bridge *bridge,
  			 struct drm_connector *connector);
  struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
  				 struct drm_connector *connector);
  void drm_bridge_hpd_enable(struct drm_bridge *bridge,
  			   void (*cb)(void *data,
  				      enum drm_connector_status status),
  			   void *data);
  void drm_bridge_hpd_disable(struct drm_bridge *bridge);
  void drm_bridge_hpd_notify(struct drm_bridge *bridge,
  			   enum drm_connector_status status);
  
  #ifdef CONFIG_DRM_PANEL_BRIDGE
  struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel);
  struct drm_bridge *drm_panel_bridge_add_typed(struct drm_panel *panel,
  					      u32 connector_type);
  void drm_panel_bridge_remove(struct drm_bridge *bridge);
  struct drm_bridge *devm_drm_panel_bridge_add(struct device *dev,
  					     struct drm_panel *panel);
  struct drm_bridge *devm_drm_panel_bridge_add_typed(struct device *dev,
  						   struct drm_panel *panel,
  						   u32 connector_type);
  struct drm_connector *drm_panel_bridge_connector(struct drm_bridge *bridge);
  #endif
  
  #if defined(CONFIG_OF) && defined(CONFIG_DRM_PANEL_BRIDGE)
  struct drm_bridge *devm_drm_of_get_bridge(struct device *dev, struct device_node *node,
  					  u32 port, u32 endpoint);
  #else
  static inline struct drm_bridge *devm_drm_of_get_bridge(struct device *dev,
  							struct device_node *node,
  							u32 port,
  							u32 endpoint)
  {
  	return ERR_PTR(-ENODEV);
  }
  #endif
  
  #endif
  