Re: [PATCH] drm/i915/dp: Enable DSC on external DP display if VBT allows

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

On Tue, 27 May 2025, Lee Shawn C <shawn.c.lee@intel.com> wrote:
> A DSC setting has been available in VBT since version 251, which allows
> users to enable or disable the DSC feature based on their system design.
> With this in mind, DP driver should reference this setting and avoid
> enabling DSC if this value is not allowed.
>
> Cc: Shankar Uma <uma.shankar@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bios.c   |  8 ++++++++
>  drivers/gpu/drm/i915/display/intel_bios.h   |  1 +
>  drivers/gpu/drm/i915/display/intel_dp.c     | 12 +++++++++---
>  drivers/gpu/drm/i915/display/intel_dp.h     |  2 +-
>  drivers/gpu/drm/i915/display/intel_dp_mst.c |  2 +-
>  5 files changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index ba7b8938b17c..f08dd54fe4d4 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -3548,6 +3548,14 @@ bool intel_bios_get_dsc_params(struct intel_encoder *encoder,
>  	return false;
>  }
>  
> +bool intel_bios_encoder_ext_display_dsc_disabled(const struct intel_bios_encoder_data *devdata)

Prefer positive instead of negative, and follow naming conventions.

intel_bios_encoder_supports_dsc().

> +{
> +	if (!devdata || devdata->display->vbt.version < 251)
> +		return false;
> +
> +	return devdata->child.disable_compression_for_ext_disp;
> +}
> +
>  static const u8 adlp_aux_ch_map[] = {
>  	[AUX_CH_A] = DP_AUX_A,
>  	[AUX_CH_B] = DP_AUX_B,
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.h b/drivers/gpu/drm/i915/display/intel_bios.h
> index 6cd7a011b8c4..901ba63e205d 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.h
> +++ b/drivers/gpu/drm/i915/display/intel_bios.h
> @@ -258,6 +258,7 @@ bool intel_bios_encoder_supports_dp_dual_mode(const struct intel_bios_encoder_da
>  bool intel_bios_encoder_is_lspcon(const struct intel_bios_encoder_data *devdata);
>  bool intel_bios_encoder_lane_reversal(const struct intel_bios_encoder_data *devdata);
>  bool intel_bios_encoder_hpd_invert(const struct intel_bios_encoder_data *devdata);
> +bool intel_bios_encoder_ext_display_dsc_disabled(const struct intel_bios_encoder_data *devdata);
>  enum port intel_bios_encoder_port(const struct intel_bios_encoder_data *devdata);
>  enum aux_ch intel_bios_dp_aux_ch(const struct intel_bios_encoder_data *devdata);
>  int intel_bios_dp_boost_level(const struct intel_bios_encoder_data *devdata);
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 640c43bf62d4..eb1e6de0148a 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1389,9 +1389,11 @@ int intel_dp_num_joined_pipes(struct intel_dp *intel_dp,
>  	return 1;
>  }
>  
> -bool intel_dp_has_dsc(const struct intel_connector *connector)
> +bool intel_dp_has_dsc(struct intel_dp *intel_dp,

There's no need to pass that in.

> +		      const struct intel_connector *connector)
>  {
>  	struct intel_display *display = to_intel_display(connector);
> +	struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
>  
>  	if (!HAS_DSC(display))
>  		return false;
> @@ -1403,6 +1405,10 @@ bool intel_dp_has_dsc(const struct intel_connector *connector)
>  	    connector->panel.vbt.edp.dsc_disable)
>  		return false;
>  
> +	if (connector->base.connector_type == DRM_MODE_CONNECTOR_DisplayPort &&

It's just absolutely bonkers that the field is for external HDMI/DP,
there's a separate field for eDP DSC disable, and there's a separate
field for DSI DSC.

Anyway, I am wondering if the output type check should be in
intel_bios_encoder_supports_dsc() instead.

(intel_bios_encoder_supports_dp() && !intel_bios_encoder_supports_edp()) ||
intel_bios_encoder_supports_hdmi().

BR,
Jani.

> +	    intel_bios_encoder_ext_display_dsc_disabled(encoder->devdata))
> +		return false;
> +
>  	if (!drm_dp_sink_supports_dsc(connector->dp.dsc_dpcd))
>  		return false;
>  
> @@ -1463,7 +1469,7 @@ intel_dp_mode_valid(struct drm_connector *_connector,
>  	mode_rate = intel_dp_link_required(target_clock,
>  					   intel_dp_mode_min_output_bpp(connector, mode));
>  
> -	if (intel_dp_has_dsc(connector)) {
> +	if (intel_dp_has_dsc(intel_dp, connector)) {
>  		enum intel_output_format sink_format, output_format;
>  		int pipe_bpp;
>  
> @@ -1650,7 +1656,7 @@ bool intel_dp_supports_dsc(struct intel_dp *intel_dp,
>  			   const struct intel_connector *connector,
>  			   const struct intel_crtc_state *crtc_state)
>  {
> -	if (!intel_dp_has_dsc(connector))
> +	if (!intel_dp_has_dsc(intel_dp, connector))
>  		return false;
>  
>  	if (intel_crtc_has_type(crtc_state, INTEL_OUTPUT_DP) &&
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
> index 742ae26ac4a9..309dad5b1b47 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> @@ -83,7 +83,7 @@ void intel_dp_audio_compute_config(struct intel_encoder *encoder,
>  bool intel_dp_has_hdmi_sink(struct intel_dp *intel_dp);
>  bool intel_dp_is_edp(struct intel_dp *intel_dp);
>  bool intel_dp_is_uhbr(const struct intel_crtc_state *crtc_state);
> -bool intel_dp_has_dsc(const struct intel_connector *connector);
> +bool intel_dp_has_dsc(struct intel_dp *intel_dp, const struct intel_connector *connector);
>  int intel_dp_link_symbol_size(int rate);
>  int intel_dp_link_symbol_clock(int rate);
>  bool intel_dp_is_port_edp(struct intel_display *display, enum port port);
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index c1fd6aceec2c..4f18059d9913 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -1508,7 +1508,7 @@ mst_connector_mode_valid_ctx(struct drm_connector *_connector,
>  		return 0;
>  	}
>  
> -	if (intel_dp_has_dsc(connector)) {
> +	if (intel_dp_has_dsc(intel_dp, connector)) {
>  		/*
>  		 * TBD pass the connector BPC,
>  		 * for now U8_MAX so that max BPC on that platform would be picked

-- 
Jani Nikula, Intel