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:
> On Tue, 27 May 2025, Jani Nikula <jani.nikula@linux.intel.com> wrote:
>>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().
>>
>
> Sure! I will rename this function.
>
>>> +{
>>> +	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.
>>
>
> intel_bios_encoder_supports_dsc() need intel_bios_encoder_data.
> That's why we pass intel_dp and use it to get ecoder data.
> Do you mean we can get encoder data from intel_connector?

You call intel_dp_has_dsc() from e.g. intel_dp_mode_valid() and that
figures out intel_dp from connector too. There's no need to pass
intel_dp around.

>
>>> +		      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().
>>
>
> Sounds good! Let's move this checking into intel_bios_encoder_supports_dsc().

Hmm, one question though. Since the VBT field is so poorly documented,
should it apply to DP MST as well?!

BR,
Jani.


>
> Best regards,
> Shawn
>
>>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
>>

-- 
Jani Nikula, Intel