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

[Kory Maincent]

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 at 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
https://bootlin.com