Re: [PATCH v2 4/6] drm/i915/mst: use the MST mode detected previously

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

On Tue, Feb 13, 2024 at 01:30:59PM +0200, Jani Nikula wrote:
> Drop the duplicate read of DP_MSTM_CAP DPCD register, and the duplicate
> logic for choosing MST mode, and store the chosen mode in struct
> intel_dp. Rename intel_dp_configure_mst() to intel_dp_mst_configure()
> while at it.
> 
> 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>
> ---
>  .../drm/i915/display/intel_display_types.h    |  1 +
>  drivers/gpu/drm/i915/display/intel_dp.c       | 23 ++++++++-----------
>  2 files changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 01eb6e4e6049..4a8440a3a812 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1780,6 +1780,7 @@ struct intel_dp {
>  
>  	bool is_mst;
>  	int active_mst_links;
> +	enum drm_dp_mst_mode mst_detect;
>  
>  	/* connector directly attached - won't be use for modeset in mst world */
>  	struct intel_connector *attached_connector;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 007cb2a04e38..72e91322e310 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -4039,11 +4039,10 @@ 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;
>  	enum drm_dp_mst_mode sink_mst_mode;
> -	enum drm_dp_mst_mode mst_detect;
>  
>  	sink_mst_mode = drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd);
>  
> -	mst_detect = intel_dp_mst_mode_choose(intel_dp, sink_mst_mode);
> +	intel_dp->mst_detect = intel_dp_mst_mode_choose(intel_dp, sink_mst_mode);
>  
>  	drm_dbg_kms(&i915->drm,
>  		    "[ENCODER:%d:%s] MST support: port: %s, sink: %s, modparam: %s -> enable: %s\n",
> @@ -4051,25 +4050,23 @@ intel_dp_mst_detect(struct intel_dp *intel_dp)
>  		    str_yes_no(intel_dp_mst_source_support(intel_dp)),
>  		    intel_dp_mst_mode_str(sink_mst_mode),
>  		    str_yes_no(i915->display.params.enable_dp_mst),
> -		    intel_dp_mst_mode_str(mst_detect));
> +		    intel_dp_mst_mode_str(intel_dp->mst_detect));
>  
> -	return mst_detect != DRM_DP_SST;
> +	return intel_dp->mst_detect != DRM_DP_SST;
>  }
>  
>  static void
> -intel_dp_configure_mst(struct intel_dp *intel_dp)
> +intel_dp_mst_configure(struct intel_dp *intel_dp)
>  {
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	bool sink_can_mst = drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd) == DRM_DP_MST;
> -
>  	if (!intel_dp_mst_source_support(intel_dp))
>  		return;

I was wondering if we even need that, but it looks to be just a
check to see if we actually initialized the mst_mgt or not.
We should probably rename it or something... Or perhaps we could
tweak the topology manager a bit so we wouldn't need to check...

>  
> -	intel_dp->is_mst = sink_can_mst &&
> -		i915->display.params.enable_dp_mst;
> +	intel_dp->is_mst = intel_dp->mst_detect != DRM_DP_SST;
> +
> +	drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr, intel_dp->is_mst);
>  
> -	drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr,
> -					intel_dp->is_mst);
> +	/* Avoid stale info on the next detect cycle. */
> +	intel_dp->mst_detect = DRM_DP_SST;

Hmm. Not sure I like having ephemeral stuff like this in intel_dp,
but I guess the alternative would be plumb it up from detect_dpcd()
by hand, which might not be super pretty either. Oh well.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  }
>  
>  static bool
> @@ -5739,7 +5736,7 @@ 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