Re: [RFC 2/4] drm/i915/dp: refactor DP MST detection and configuration

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Feb 02, 2024 at 04:05:32PM +0200, Jani Nikula wrote:
> Currently we've split MST capability detection in two places,
> intel_dp_can_mst() and intel_dp_configure_mst(). They check essentially
> the same things.
> 
> Move bulk of the work, including logging, to intel_dp_can_mst() and
> rename it intel_dp_mst_detect(). Set intel_dp->is_mst there to avoid
> duplicate work.

This seems confusing. is_mst is supposed to reflect the state
of the topology manager, nothing more.

> 
> Rename intel_dp_configure_mst() to intel_dp_mst_configure(), and only
> set the topology manager state there.
> 
> The main functional difference is that the DP_MSTM_CAP DPCD register is
> now only read once at detect, unconditionally, and the MST support is
> always logged. Everything else should remain the same.
> 
> Cc: Arun R Murthy <arun.r.murthy@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 36 ++++++++++---------------
>  1 file changed, 14 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 7af09f2c008d..e0b8ee6bde79 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -4004,23 +4004,15 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  					   intel_dp->downstream_ports) == 0;
>  }
>  
> -static bool
> -intel_dp_can_mst(struct intel_dp *intel_dp)
> +static bool intel_dp_mst_detect(struct intel_dp *intel_dp)
>  {
>  	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> +	struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
> +	bool sink_can_mst = drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd) == DP_MST_CAPABLE;
>  
> -	return i915->display.params.enable_dp_mst &&
> +	intel_dp->is_mst = i915->display.params.enable_dp_mst &&
>  		intel_dp_mst_source_support(intel_dp) &&
> -		drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd) == DP_MST_CAPABLE;
> -}
> -
> -static void
> -intel_dp_configure_mst(struct intel_dp *intel_dp)
> -{
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	struct intel_encoder *encoder =
> -		&dp_to_dig_port(intel_dp)->base;
> -	bool sink_can_mst = drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd) == DP_MST_CAPABLE;
> +		sink_can_mst;
>  
>  	drm_dbg_kms(&i915->drm,
>  		    "[ENCODER:%d:%s] MST support: port: %s, sink: %s, modparam: %s\n",
> @@ -4029,14 +4021,14 @@ intel_dp_configure_mst(struct intel_dp *intel_dp)
>  		    str_yes_no(sink_can_mst),
>  		    str_yes_no(i915->display.params.enable_dp_mst));
>  
> -	if (!intel_dp_mst_source_support(intel_dp))
> -		return;
> -
> -	intel_dp->is_mst = sink_can_mst &&
> -		i915->display.params.enable_dp_mst;
> +	return intel_dp->is_mst;
> +}
>  
> -	drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr,
> -					intel_dp->is_mst);
> +static void intel_dp_mst_configure(struct intel_dp *intel_dp)
> +{
> +	if (intel_dp_mst_source_support(intel_dp))
> +		drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr,
> +						intel_dp->is_mst);
>  }
>  
>  static bool
> @@ -5387,7 +5379,7 @@ intel_dp_detect_dpcd(struct intel_dp *intel_dp)
>  		connector_status_connected : connector_status_disconnected;
>  	}
>  
> -	if (intel_dp_can_mst(intel_dp))
> +	if (intel_dp_mst_detect(intel_dp))
>  		return connector_status_connected;
>  
>  	/* If no HPD, poke DDC gently */
> @@ -5706,7 +5698,7 @@ intel_dp_detect(struct drm_connector *connector,
>  
>  	intel_dp_detect_dsc_caps(intel_dp, intel_connector);
>  
> -	intel_dp_configure_mst(intel_dp);
> +	intel_dp_mst_configure(intel_dp);
>  
>  	/*
>  	 * TODO: Reset link params when switching to MST mode, until MST
> -- 
> 2.39.2

-- 
Ville Syrjälä
Intel