本文参考以下博文：
Linux内核4.14版本------drm框架分析(2)------connector分析
特此致谢！
1. 简介
connector是指encoder和panel之间交互的接口部分，更通俗地说就是连接物理设备的连接器，对应于物理连接器 (如VGA、DVI、FPD-Link、HDMI、DisplayPort、S-Video等) 。connector并不是指物理线，在DRM中，connector 是一个抽象的数据结构，代表连接的显示设备，从connector中可以得到当前物理连接的输出设备相关的信息。
connector通常和encoder驱动绑定在一起。
connector在系统中的位置和作用如下所示：
2. 核心结构
在Linux内核的DRM中，connector对应的核心结构体为：struct drm_connector。该结构体在include/drm/drm_connector.h中定义，代码如下（Linux内核版本：6.1）：
cpp
/**
* struct drm_connector - central DRM connector control structure
*
* Each connector may be connected to one or more CRTCs, or may be clonable by
* another connector if they can share a CRTC. Each connector also has a specific
* position in the broader display (referred to as a 'screen' though it could
* span multiple monitors).
*/
struct drm_connector {
/** @dev: parent DRM device */
struct drm_device *dev;
/** @kdev: kernel device for sysfs attributes */
struct device *kdev;
/** @attr: sysfs attributes */
struct device_attribute *attr;
/**
* @fwnode: associated fwnode supplied by platform firmware
*
* Drivers can set this to associate a fwnode with a connector, drivers
* are expected to get a reference on the fwnode when setting this.
* drm_connector_cleanup() will call fwnode_handle_put() on this.
*/
struct fwnode_handle *fwnode;
/**
* @head:
*
* List of all connectors on a @dev, linked from
* &drm_mode_config.connector_list. Protected by
* &drm_mode_config.connector_list_lock, but please only use
* &drm_connector_list_iter to walk this list.
*/
struct list_head head;
/**
* @global_connector_list_entry:
*
* Connector entry in the global connector-list, used by
* drm_connector_find_by_fwnode().
*/
struct list_head global_connector_list_entry;
/** @base: base KMS object */
struct drm_mode_object base;
/** @name: human readable name, can be overwritten by the driver */
char *name;
/**
* @mutex: Lock for general connector state, but currently only protects
* @registered. Most of the connector state is still protected by
* &drm_mode_config.mutex.
*/
struct mutex mutex;
/**
* @index: Compacted connector index, which matches the position inside
* the mode_config.list for drivers not supporting hot-add/removing. Can
* be used as an array index. It is invariant over the lifetime of the
* connector.
*/
unsigned index;
/**
* @connector_type:
* one of the DRM_MODE_CONNECTOR_<foo> types from drm_mode.h
*/
int connector_type;
/** @connector_type_id: index into connector type enum */
int connector_type_id;
/**
* @interlace_allowed:
* Can this connector handle interlaced modes? Only used by
* drm_helper_probe_single_connector_modes() for mode filtering.
*/
bool interlace_allowed;
/**
* @doublescan_allowed:
* Can this connector handle doublescan? Only used by
* drm_helper_probe_single_connector_modes() for mode filtering.
*/
bool doublescan_allowed;
/**
* @stereo_allowed:
* Can this connector handle stereo modes? Only used by
* drm_helper_probe_single_connector_modes() for mode filtering.
*/
bool stereo_allowed;
/**
* @ycbcr_420_allowed : This bool indicates if this connector is
* capable of handling YCBCR 420 output. While parsing the EDID
* blocks it's very helpful to know if the source is capable of
* handling YCBCR 420 outputs.
*/
bool ycbcr_420_allowed;
/**
* @registration_state: Is this connector initializing, exposed
* (registered) with userspace, or unregistered?
*
* Protected by @mutex.
*/
enum drm_connector_registration_state registration_state;
/**
* @modes:
* Modes available on this connector (from fill_modes() + user).
* Protected by &drm_mode_config.mutex.
*/
struct list_head modes;
/**
* @status:
* One of the drm_connector_status enums (connected, not, or unknown).
* Protected by &drm_mode_config.mutex.
*/
enum drm_connector_status status;
/**
* @probed_modes:
* These are modes added by probing with DDC or the BIOS, before
* filtering is applied. Used by the probe helpers. Protected by
* &drm_mode_config.mutex.
*/
struct list_head probed_modes;
/**
* @display_info: Display information is filled from EDID information
* when a display is detected. For non hot-pluggable displays such as
* flat panels in embedded systems, the driver should initialize the
* &drm_display_info.width_mm and &drm_display_info.height_mm fields
* with the physical size of the display.
*
* Protected by &drm_mode_config.mutex.
*/
struct drm_display_info display_info;
/** @funcs: connector control functions */
const struct drm_connector_funcs *funcs;
/**
* @edid_blob_ptr: DRM property containing EDID if present. Protected by
* &drm_mode_config.mutex. This should be updated only by calling
* drm_connector_update_edid_property().
*/
struct drm_property_blob *edid_blob_ptr;
/** @properties: property tracking for this connector */
struct drm_object_properties properties;
/**
* @scaling_mode_property: Optional atomic property to control the
* upscaling. See drm_connector_attach_content_protection_property().
*/
struct drm_property *scaling_mode_property;
/**
* @vrr_capable_property: Optional property to help userspace
* query hardware support for variable refresh rate on a connector.
* connector. Drivers can add the property to a connector by
* calling drm_connector_attach_vrr_capable_property().
*
* This should be updated only by calling
* drm_connector_set_vrr_capable_property().
*/
struct drm_property *vrr_capable_property;
/**
* @colorspace_property: Connector property to set the suitable
* colorspace supported by the sink.
*/
struct drm_property *colorspace_property;
/**
* @path_blob_ptr:
*
* DRM blob property data for the DP MST path property. This should only
* be updated by calling drm_connector_set_path_property().
*/
struct drm_property_blob *path_blob_ptr;
/**
* @max_bpc_property: Default connector property for the max bpc to be
* driven out of the connector.
*/
struct drm_property *max_bpc_property;
/** @privacy_screen: drm_privacy_screen for this connector, or NULL. */
struct drm_privacy_screen *privacy_screen;
/** @privacy_screen_notifier: privacy-screen notifier_block */
struct notifier_block privacy_screen_notifier;
/**
* @privacy_screen_sw_state_property: Optional atomic property for the
* connector to control the integrated privacy screen.
*/
struct drm_property *privacy_screen_sw_state_property;
/**
* @privacy_screen_hw_state_property: Optional atomic property for the
* connector to report the actual integrated privacy screen state.
*/
struct drm_property *privacy_screen_hw_state_property;
#define DRM_CONNECTOR_POLL_HPD (1 << 0)
#define DRM_CONNECTOR_POLL_CONNECT (1 << 1)
#define DRM_CONNECTOR_POLL_DISCONNECT (1 << 2)
/**
* @polled:
*
* Connector polling mode, a combination of
*
* DRM_CONNECTOR_POLL_HPD
* The connector generates hotplug events and doesn't need to be
* periodically polled. The CONNECT and DISCONNECT flags must not
* be set together with the HPD flag.
*
* DRM_CONNECTOR_POLL_CONNECT
* Periodically poll the connector for connection.
*
* DRM_CONNECTOR_POLL_DISCONNECT
* Periodically poll the connector for disconnection, without
* causing flickering even when the connector is in use. DACs should
* rarely do this without a lot of testing.
*
* Set to 0 for connectors that don't support connection status
* discovery.
*/
uint8_t polled;
/**
* @dpms: Current dpms state. For legacy drivers the
* &drm_connector_funcs.dpms callback must update this. For atomic
* drivers, this is handled by the core atomic code, and drivers must
* only take &drm_crtc_state.active into account.
*/
int dpms;
/** @helper_private: mid-layer private data */
const struct drm_connector_helper_funcs *helper_private;
/** @cmdline_mode: mode line parsed from the kernel cmdline for this connector */
struct drm_cmdline_mode cmdline_mode;
/** @force: a DRM_FORCE_<foo> state for forced mode sets */
enum drm_connector_force force;
/**
* @override_edid: has the EDID been overwritten through debugfs for
* testing? Do not modify outside of drm_edid_override_set() and
* drm_edid_override_reset().
*/
bool override_edid;
/** @epoch_counter: used to detect any other changes in connector, besides status */
u64 epoch_counter;
/**
* @possible_encoders: Bit mask of encoders that can drive this
* connector, drm_encoder_index() determines the index into the bitfield
* and the bits are set with drm_connector_attach_encoder().
*/
u32 possible_encoders;
/**
* @encoder: Currently bound encoder driving this connector, if any.
* Only really meaningful for non-atomic drivers. Atomic drivers should
* instead look at &drm_connector_state.best_encoder, and in case they
* need the CRTC driving this output, &drm_connector_state.crtc.
*/
struct drm_encoder *encoder;
#define MAX_ELD_BYTES 128
/** @eld: EDID-like data, if present */
uint8_t eld[MAX_ELD_BYTES];
/** @latency_present: AV delay info from ELD, if found */
bool latency_present[2];
/**
* @video_latency: Video latency info from ELD, if found.
* [0]: progressive, [1]: interlaced
*/
int video_latency[2];
/**
* @audio_latency: audio latency info from ELD, if found
* [0]: progressive, [1]: interlaced
*/
int audio_latency[2];
/**
* @ddc: associated ddc adapter.
* A connector usually has its associated ddc adapter. If a driver uses
* this field, then an appropriate symbolic link is created in connector
* sysfs directory to make it easy for the user to tell which i2c
* adapter is for a particular display.
*
* The field should be set by calling drm_connector_init_with_ddc().
*/
struct i2c_adapter *ddc;
/**
* @null_edid_counter: track sinks that give us all zeros for the EDID.
* Needed to workaround some HW bugs where we get all 0s
*/
int null_edid_counter;
/** @bad_edid_counter: track sinks that give us an EDID with invalid checksum */
unsigned bad_edid_counter;
/**
* @edid_corrupt: Indicates whether the last read EDID was corrupt. Used
* in Displayport compliance testing - Displayport Link CTS Core 1.2
* rev1.1 4.2.2.6
*/
bool edid_corrupt;
/**
* @real_edid_checksum: real edid checksum for corrupted edid block.
* Required in Displayport 1.4 compliance testing
* rev1.1 4.2.2.6
*/
u8 real_edid_checksum;
/** @debugfs_entry: debugfs directory for this connector */
struct dentry *debugfs_entry;
/**
* @state:
*
* Current atomic state for this connector.
*
* This is protected by &drm_mode_config.connection_mutex. Note that
* nonblocking atomic commits access the current connector state without
* taking locks. Either by going through the &struct drm_atomic_state
* pointers, see for_each_oldnew_connector_in_state(),
* for_each_old_connector_in_state() and
* for_each_new_connector_in_state(). Or through careful ordering of
* atomic commit operations as implemented in the atomic helpers, see
* &struct drm_crtc_commit.
*/
struct drm_connector_state *state;
/* DisplayID bits. FIXME: Extract into a substruct? */
/**
* @tile_blob_ptr:
*
* DRM blob property data for the tile property (used mostly by DP MST).
* This is meant for screens which are driven through separate display
* pipelines represented by &drm_crtc, which might not be running with
* genlocked clocks. For tiled panels which are genlocked, like
* dual-link LVDS or dual-link DSI, the driver should try to not expose
* the tiling and virtualize both &drm_crtc and &drm_plane if needed.
*
* This should only be updated by calling
* drm_connector_set_tile_property().
*/
struct drm_property_blob *tile_blob_ptr;
/** @has_tile: is this connector connected to a tiled monitor */
bool has_tile;
/** @tile_group: tile group for the connected monitor */
struct drm_tile_group *tile_group;
/** @tile_is_single_monitor: whether the tile is one monitor housing */
bool tile_is_single_monitor;
/** @num_h_tile: number of horizontal tiles in the tile group */
/** @num_v_tile: number of vertical tiles in the tile group */
uint8_t num_h_tile, num_v_tile;
/** @tile_h_loc: horizontal location of this tile */
/** @tile_v_loc: vertical location of this tile */
uint8_t tile_h_loc, tile_v_loc;
/** @tile_h_size: horizontal size of this tile. */
/** @tile_v_size: vertical size of this tile. */
uint16_t tile_h_size, tile_v_size;
/**
* @free_node:
*
* List used only by &drm_connector_list_iter to be able to clean up a
* connector from any context, in conjunction with
* &drm_mode_config.connector_free_work.
*/
struct llist_node free_node;
/** @hdr_sink_metadata: HDR Metadata Information read from sink */
struct hdr_sink_metadata hdr_sink_metadata;
};可以看到，这个结构比plane、CRTC和encoder大得多。
3. drm_connector结构释义
（0）总述
cpp
/**
* struct drm_connector - central DRM connector control structure
*
* Each connector may be connected to one or more CRTCs, or may be clonable by
* another connector if they can share a CRTC. Each connector also has a specific
* position in the broader display (referred to as a 'screen' though it could
* span multiple monitors).
*/struct drm_connector ------ 核心的DRM connector控制结构。
每个connector可以连接到一个或多个CRTC，或者如果它们可以共享CRTC，则可以由另一个connector克隆。每个connector在更宽的显示中也有一个特定的位置（称为"屏幕"，尽管它可以跨越多个监视器）。
（1）struct drm_device *dev
cpp
/** @dev: parent DRM device */
struct drm_device *dev;父DRM设备。
（2）struct device *kdev
cpp
/** @kdev: kernel device for sysfs attributes */
struct device *kdev;sysfs属性的内核设备。
（3）struct device_attribute *attr
cpp
/** @attr: sysfs attributes */
struct device_attribute *attr;sysfs属性。
（4）struct fwnode_handle *fwnode
cpp
/**
* @fwnode: associated fwnode supplied by platform firmware
*
* Drivers can set this to associate a fwnode with a connector, drivers
* are expected to get a reference on the fwnode when setting this.
* drm_connector_cleanup() will call fwnode_handle_put() on this.
*/
struct fwnode_handle *fwnode;由平台固件提供的关联fwnode。
驱动程序可以将此项设置为将fwnode与一个connector相关联，在设置此项时，驱动程序需要在fwnode上获得引用。在如此设置后，drm_connector_cleanup()将调用fwnode_handle_put()。
（5）struct list_head head
cpp
/**
* @head:
*
* List of all connectors on a @dev, linked from
* &drm_mode_config.connector_list. Protected by
* &drm_mode_config.connector_list_lock, but please only use
* &drm_connector_list_iter to walk this list.
*/
struct list_head head;从&drm_mode_config.connecter_List链接的@dev上所有连接器的列表。受&drm_mode_config.connector_list_lock保护，但请仅使用&drm_conconnector_list_iter遍历此链表。
（6）struct list_head global_connector_list_entry
cpp
/**
* @global_connector_list_entry:
*
* Connector entry in the global connector-list, used by
* drm_connector_find_by_fwnode().
*/
struct list_head global_connector_list_entry;全局connector-list中的connector条目，由drm_connector_find_by_fwnode()使用。
（7）struct drm_mode_object base
cpp
/** @base: base KMS object */
struct drm_mode_object base;基本KMS对象。
（8）char *name
cpp
/** @name: human readable name, can be overwritten by the driver */
char *name;人类可读的名称（名字），可以被驱动程序覆盖。
drm_connector结构的其余成员将在下一篇文章中继续深入释义。