[PATCH RFC 00/12] Add support for DisplayPort link training information report

Kory Maincent
2026-04-09T17:09:03Z

DisplayPort link training negotiates the physical-layer parameters needed
for a reliable connection: lane count, link rate, voltage swing,
pre-emphasis, and optionally Display Stream Compression (DSC). Currently,
each driver exposes this state in its own way, often through
driver-specific debugfs entries, with no standard interface for userspace
diagnostic and monitoring tools.

This series introduces a generic, DRM-managed framework for exposing DP
link training state as standard connector properties, modeled after the
existing HDMI helper drmm_connector_hdmi_init().

The new drmm_connector_dp_init() helper initializes a DP connector and
registers the following connector properties to expose the negotiated link
state to userspace:

- num_lanes: negotiated lane count (1, 2 or 4)
- link_rate: negotiated link rate
- dsc_en: whether Display Stream Compression is active
- voltage_swingN: per-lane voltage swing level (lanes 0-3)
- pre_emphasisN: per-lane pre-emphasis level (lanes 0-3)

Two runtime helpers update and clear these properties when link training
completes or the link goes down:
- drm_connector_dp_set_link_train_properties()
- drm_connector_dp_reset_link_train_properties()

Two drivers are updated as reference implementations: i915 (direct
connector path) and MediaTek (via the bridge connector framework using a
new DRM_BRIDGE_OP_DP flag). The i915 patches are preceded by a series of
conversions to DRM managed resources, which are required before adopting
drmm_connector_dp_init().

The MST case in i915 driver is not supported yet.

Patches 1-3: Fix two error-path cleanup bugs in i915 sdvo and lvds
[Will probably be sent standalone]
Patches 4-8: Convert i915 display resources to DRM managed lifetime
Patch 9: Introduce the core drmm_connector_dp_init() framework
Patch 10: Wire the i915 DP connector to use the new helpers
Patch 11: Introduce DRM_BRIDGE_OP_DP and wire bridge connectors
Patch 12: Wire the MediaTek DP bridge to the new helpers [untested]

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
---
Kory Maincent (12):
drm/i915/display/intel_sdvo: Fix double connector destroy in error paths
drm/i915/display/intel_lvds: Drop redundant manual cleanup on init failure
drm/i915/display/intel_dp: Drop redundant intel_dp_aux_fini() on init failure
drm/i915/display: Switch to drmm_mode_config_init() and drop manual cleanup
drm/i915/display: Switch to managed for crtc
drm/i915/display: Switch to managed for plane
drm/i915/display: Switch to managed for encoder
drm/i915/display: Switch to managed for connector
drm: Introduce drmm_connector_dp_init() with link training state properties
drm/i915/display/dp: Adopt dp_connector helpers to expose link training state
drm/bridge: Wire drmm_connector_dp_init() via new DRM_BRIDGE_OP_DP flag
drm/mediatek: Use dp_connector helpers to report link training state

drivers/gpu/drm/Makefile | 1 +
drivers/gpu/drm/display/drm_bridge_connector.c | 26 +-
drivers/gpu/drm/drm_dp_connector.c | 344 +++++++++++++++++++++
drivers/gpu/drm/i915/display/g4x_dp.c | 39 +--
drivers/gpu/drm/i915/display/g4x_hdmi.c | 27 +-
drivers/gpu/drm/i915/display/i9xx_plane.c | 97 +++---
drivers/gpu/drm/i915/display/icl_dsi.c | 50 ++-
drivers/gpu/drm/i915/display/intel_connector.c | 26 +-
drivers/gpu/drm/i915/display/intel_connector.h | 5 +-
drivers/gpu/drm/i915/display/intel_crt.c | 28 +-
drivers/gpu/drm/i915/display/intel_crtc.c | 102 +++---
drivers/gpu/drm/i915/display/intel_cursor.c | 41 ++-
drivers/gpu/drm/i915/display/intel_ddi.c | 64 ++--
drivers/gpu/drm/i915/display/intel_display.c | 8 -
drivers/gpu/drm/i915/display/intel_display.h | 1 -
.../gpu/drm/i915/display/intel_display_driver.c | 37 ++-
drivers/gpu/drm/i915/display/intel_dp.c | 43 ++-
.../gpu/drm/i915/display/intel_dp_link_training.c | 25 ++
drivers/gpu/drm/i915/display/intel_dp_mst.c | 33 +-
drivers/gpu/drm/i915/display/intel_dvo.c | 43 +--
drivers/gpu/drm/i915/display/intel_encoder.c | 6 +-
drivers/gpu/drm/i915/display/intel_encoder.h | 3 +-
drivers/gpu/drm/i915/display/intel_hdmi.c | 15 +-
drivers/gpu/drm/i915/display/intel_lvds.c | 45 ++-
drivers/gpu/drm/i915/display/intel_plane.c | 45 +--
drivers/gpu/drm/i915/display/intel_plane.h | 5 +-
drivers/gpu/drm/i915/display/intel_sdvo.c | 134 +++-----
drivers/gpu/drm/i915/display/intel_sprite.c | 119 ++++---
drivers/gpu/drm/i915/display/intel_tv.c | 26 +-
drivers/gpu/drm/i915/display/skl_universal_plane.c | 102 +++---
drivers/gpu/drm/i915/display/vlv_dsi.c | 42 +--
drivers/gpu/drm/mediatek/mtk_dp.c | 34 +-
include/drm/drm_bridge.h | 13 +
include/drm/drm_connector.h | 38 +++
include/drm/drm_dp_connector.h | 109 +++++++
35 files changed, 1125 insertions(+), 651 deletions(-)
---
base-commit: db5a75cfd29766536be62aece9f19c6e7a858fa6
change-id: 20260226-feat_link_cap-20cbb6f31d40

Best regards,
--
Köry Maincent, Bootlin
Embedded Linux and kernel engineering