Re: [PATCH RFC 10/12] drm/i915/display/dp: Adopt dp_connector helpers to expose link training state

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 09 Apr 2026, Kory Maincent <kory.maincent@bootlin.com> wrote:
> Switch the i915 DP connector initialization from drmm_connector_init()
> to drmm_connector_dp_init(), providing the source link capabilities
> (supported lane counts, link rates, DSC support, voltage swing and
> pre-emphasis levels).
>
> Add intel_dp_report_link_train() to collect the negotiated link
> parameters (rate, lane count, DSC enable, per-lane voltage swing and
> pre-emphasis) and report them via drm_connector_dp_set_link_train_properties()
> once link training completes successfully.
>
> Reset the link training properties via
> drm_connector_dp_reset_link_train_properties() when the connector is
> reported as disconnected or when the display device is disabled, so
> the exposed state always reflects the current link status.
>
> Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c            | 31 +++++++++++++++++++---
>  .../gpu/drm/i915/display/intel_dp_link_training.c  | 25 +++++++++++++++++
>  2 files changed, 52 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 2af64de9c81de..641406bdc0cc9 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -45,6 +45,7 @@
>  #include <drm/display/drm_hdmi_helper.h>
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_crtc.h>
> +#include <drm/drm_dp_connector.h>
>  #include <drm/drm_edid.h>
>  #include <drm/drm_fixed.h>
>  #include <drm/drm_managed.h>
> @@ -6337,8 +6338,10 @@ intel_dp_detect(struct drm_connector *_connector,
>  	drm_WARN_ON(display->drm,
>  		    !drm_modeset_is_locked(&display->drm->mode_config.connection_mutex));
>  
> -	if (!intel_display_device_enabled(display))
> +	if (!intel_display_device_enabled(display)) {
> +		drm_connector_dp_reset_link_train_properties(_connector);
>  		return connector_status_disconnected;
> +	}
>  
>  	if (!intel_display_driver_check_access(display))
>  		return connector->base.status;
> @@ -6388,6 +6391,8 @@ intel_dp_detect(struct drm_connector *_connector,
>  
>  		intel_dp_tunnel_disconnect(intel_dp);
>  
> +		drm_connector_dp_reset_link_train_properties(_connector);
> +
>  		goto out_unset_edid;
>  	}
>  
> @@ -7162,10 +7167,12 @@ intel_dp_init_connector(struct intel_digital_port *dig_port,
>  			struct intel_connector *connector)
>  {
>  	struct intel_display *display = to_intel_display(dig_port);
> +	struct drm_connector_dp_link_train_caps link_caps;
>  	struct intel_dp *intel_dp = &dig_port->dp;
>  	struct intel_encoder *encoder = &dig_port->base;
>  	struct drm_device *dev = encoder->base.dev;
>  	enum port port = encoder->port;
> +	u32 *rates;
>  	int type;
>  
>  	if (drm_WARN(dev, dig_port->max_lanes < 1,
> @@ -7213,8 +7220,25 @@ intel_dp_init_connector(struct intel_digital_port *dig_port,
>  		    type == DRM_MODE_CONNECTOR_eDP ? "eDP" : "DP",
>  		    encoder->base.base.id, encoder->base.name);
>  
> -	drmm_connector_init(dev, &connector->base, &intel_dp_connector_funcs,
> -			    type, &intel_dp->aux.ddc);
> +	intel_dp_set_source_rates(intel_dp);
> +	link_caps.nlanes = DRM_DP_1LANE | DRM_DP_2LANE | DRM_DP_4LANE;
> +	link_caps.nrates = intel_dp->num_source_rates;
> +	rates = kzalloc_objs(*rates, intel_dp->num_source_rates);
> +	if (!rates)
> +		goto fail;
> +
> +	for (int i = 0; i < intel_dp->num_source_rates; i++)
> +		rates[i] = intel_dp->source_rates[i];
> +
> +	link_caps.rates = rates;
> +	link_caps.dsc = true;

You have a source, you have a sink, and you have a link between the two.

Source rates do not reflect the link rates common between source and
sink.

DSC depends on source and sink, and it's not statically "true" for
either, and depends on a bunch of things.

BR,
Jani.

> +	link_caps.v_swings = DRM_DP_VOLTAGE_SWING_LEVEL_MASK;
> +	link_caps.pre_emphs = DRM_DP_PRE_EMPH_LEVEL_MASK;
> +
> +	drmm_connector_dp_init(dev, &connector->base, &intel_dp_connector_funcs,
> +			       &link_caps, type, &intel_dp->aux.ddc);
> +	kfree(rates);
> +
>  	drm_connector_helper_add(&connector->base, &intel_dp_connector_helper_funcs);
>  
>  	if (drmm_add_action_or_reset(dev, intel_connector_destroy, connector)) {
> @@ -7240,7 +7264,6 @@ intel_dp_init_connector(struct intel_digital_port *dig_port,
>  	if (!intel_edp_init_connector(intel_dp, connector))
>  		goto fail;
>  
> -	intel_dp_set_source_rates(intel_dp);
>  	intel_dp_set_common_rates(intel_dp);
>  	intel_dp_reset_link_params(intel_dp);
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> index 54c585c59b900..c2fd46a323650 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -25,6 +25,7 @@
>  #include <linux/iopoll.h>
>  
>  #include <drm/display/drm_dp_helper.h>
> +#include <drm/drm_dp_connector.h>
>  #include <drm/drm_print.h>
>  
>  #include "intel_display_core.h"
> @@ -1116,6 +1117,27 @@ intel_dp_128b132b_intra_hop(struct intel_dp *intel_dp,
>  	return sink_status & DP_INTRA_HOP_AUX_REPLY_INDICATION ? 1 : 0;
>  }
>  
> +static void intel_dp_report_link_train(struct intel_dp *intel_dp)
> +{
> +	struct intel_connector *connector = intel_dp->attached_connector;
> +	struct drm_connector_dp_link_train dp_link_train;
> +
> +	dp_link_train.rate = intel_dp->link_rate;
> +	dp_link_train.nlanes = intel_dp->lane_count;
> +	dp_link_train.dsc_en = connector->dp.dsc_decompression_enabled;
> +
> +	for (int i = 0; i < intel_dp->lane_count; i++) {
> +		int v_swing_level = (intel_dp->train_set[i] &
> +				     DP_TRAIN_VOLTAGE_SWING_MASK) >> DP_TRAIN_VOLTAGE_SWING_SHIFT;
> +		int pre_emph_level = (intel_dp->train_set[i] &
> +				      DP_TRAIN_PRE_EMPHASIS_MASK) >> DP_TRAIN_PRE_EMPHASIS_SHIFT;
> +		dp_link_train.v_swing[i] = 1 << v_swing_level;
> +		dp_link_train.pre_emph[i] = 1 << pre_emph_level;
> +	}
> +
> +	drm_connector_dp_set_link_train_properties(&connector->base, &dp_link_train);
> +}
> +
>  /**
>   * intel_dp_stop_link_train - stop link training
>   * @intel_dp: DP struct
> @@ -1144,6 +1166,9 @@ void intel_dp_stop_link_train(struct intel_dp *intel_dp,
>  	intel_dp_program_link_training_pattern(intel_dp, crtc_state, DP_PHY_DPRX,
>  					       DP_TRAINING_PATTERN_DISABLE);
>  
> +	if (!intel_dp->is_mst)
> +		intel_dp_report_link_train(intel_dp);
> +
>  	if (intel_dp_is_uhbr(crtc_state)) {
>  		ret = poll_timeout_us(ret = intel_dp_128b132b_intra_hop(intel_dp, crtc_state),
>  				      ret == 0,

-- 
Jani Nikula, Intel