DisplayPort Link Capabilities

The Intel DP link caps API tracks the supported and allowed DisplayPort link configurations for a DP encoder and its attached connectors, and provides helpers to iterate over the allowed configurations and constrain them by filtering, disabling, or limiting them to maximum link parameters.

Locking

All accesses to this API must be serialized. The only exception is intel_dp_link_caps_get_max_limits(), which allow lockless lookup. Such lookups may observe an out-of-sync struct intel_dp_link_config tuple, i.e. a rate from one state and a lane count from another.

The Intel i915/xe drivers ensure the above serialization by holding drm_mode_config.connection_mutex and, while holding the lock, waiting for any pending asynchronous atomic commits. This also allows use of the API from the tails of asynchronous atomic commits, which cannot hold the lock.

Iterating and restricting link configurations

The link configuration iterators can iterate the allowed configurations during modeset configuration selection or link training fallback handling in a configurable order.

The iteration order can depend on connector type (eDP, DP SST, DP MST) and modeset-specific conditions or driver policies, such as DSC vs. non-DSC modes, power saving vs. better user experience, or policy changes after a link training failure.

The configurations exposed via the iterators can be additionally constrained in the following ways:

• Filtered for a given modeset based on modeset-specific conditions. Examples for such conditions include driver policies preferring power saving or better user experience, post-link training failure preference changes, or sink automated test requests limiting the usable configurations.

• Disabled permanently for the connected sink. Examples of reasons to disable a configuration include a link training failure for a given configuration or a driver workaround preventing the use of a particular configuration.

• Limited via a maximum link rate and lane count. For example, after a link training failure, subsequent modesets may be limited to configurations at or below the failed parameters.

  This mechanism exists for backward compatibility only. Eventually, it will be removed in favor of relying solely on individually disabled configurations, as described above.

Terminology

Common link capabilities (or common caps) refer to the link rates and maximum lane count supported by both the source and the sink, i.e. the intersection of their respective capabilities.

Supported configurations are all configurations defined by the Common link capabilities’ link rates and maximum lane count.

Disabled configurations are Supported configurations disabled via this API.

Enabled configurations are Supported configurations that are not disabled.

Forced configurations are Enabled configurations forced via forced link parameter debugfs entries.

Allowed configurations are the Enabled configurations, or if forcing is in effect the Forced configurations, constrained by a maximum rate and lane count set via the API.

enum intel_dp_link_caps_order_key

key used to order configurations

Constants

INTEL_DP_LINK_CAPS_ORDER_KEY_BW

Order configurations by bandwidth, then by link rate.

INTEL_DP_LINK_CAPS_ORDER_KEY_RATE_LANE

Order configurations by link rate, then by lane count.

INTEL_DP_LINK_CAPS_ORDER_KEY_LANE_RATE

Order configurations by lane count, then by link rate.

INTEL_DP_LINK_CAPS_ORDER_KEY_NUM

Number of ordering keys.

Description

Selects how a caller wants the configuration table to be ordered, together with an enum intel_dp_link_caps_order_direction, for iteration queries.

See also:

• struct intel_dp_link_caps_order

• intel_dp_link_caps_get_max_config()

enum intel_dp_link_caps_order_direction

iteration direction

Constants

INTEL_DP_LINK_CAPS_ORDER_DIR_ASC

Iterate in ascending order according to the selected ordering key.

INTEL_DP_LINK_CAPS_ORDER_DIR_DESC

Iterate in descending order according to the selected ordering key.

INTEL_DP_LINK_CAPS_ORDER_DIR_NUM

Number of ordering directions.

Description

Selects the direction associated with an enum intel_dp_link_caps_order_key for iteration queries.

See also:

• struct intel_dp_link_caps_order

struct intel_dp_link_caps_order

configuration ordering

Definition:

struct intel_dp_link_caps_order {
    enum intel_dp_link_caps_order_key key;
    enum intel_dp_link_caps_order_direction dir;
};

Members

key

Key used to order configurations.

dir

Direction of the selected ordering.

Description

Describes an iteration order for link configurations.

See also:

• for_each_dp_link_config()

for_each_dp_link_config

for_each_dp_link_config (__iter, __config)

iterate allowed link configurations

Parameters

__iter

struct intel_dp_link_caps_iter being iterated

__config

pointer to struct intel_dp_link_config filled for each match