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

[Ville Syrjälä]

On Thu, Apr 09, 2026 at 07:08:16PM +0200, Kory Maincent wrote:
> 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)

I don't see why any real userspace would be interested in those (apart
from maybe DSC). If this is just for diagnostics and whatnot then I
think sysfs/debugfs could be a better fit.

> 
> 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

-- 
Ville Syrjälä
Intel