Re: [Intel-gfx] [PATCH 4/6] drm/i915/dp: Ensure sink/link max lane count values are always valid

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

On Mon, Oct 18, 2021 at 12:41:52PM +0300, Imre Deak wrote:
> Print an error if the DPCD sink max lane count is invalid and fix it up.
> 
> While at it also add an assert that the link max lane count (derived
> from intel_dp_max_common_lane_count(), potentially reduced by the LT
> fallback logic) value is also valid.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  .../drm/i915/display/intel_display_types.h    |  2 +
>  drivers/gpu/drm/i915/display/intel_dp.c       | 44 ++++++++++++++++++-
>  2 files changed, 44 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 39e11eaec1a3f..1e42bf901263c 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1563,6 +1563,8 @@ struct intel_dp {
>  	int num_sink_rates;
>  	int sink_rates[DP_MAX_SUPPORTED_RATES];
>  	bool use_rate_select;
> +	/* Max sink lane count as reported by DP_MAX_LANE_COUNT */
> +	int max_sink_lane_count;
>  	/* intersection of source and sink rates */
>  	int num_common_rates;
>  	int common_rates[DP_MAX_SUPPORTED_RATES];
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 1935eb49f9574..f7711779df132 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -197,6 +197,35 @@ static void intel_dp_set_sink_rates(struct intel_dp *intel_dp)
>  	intel_dp->num_sink_rates = i;
>  }
>  
> +static void intel_dp_set_default_max_sink_lane_count(struct intel_dp *intel_dp)
> +{
> +	intel_dp->max_sink_lane_count = 1;
> +}
> +
> +static void intel_dp_set_max_sink_lane_count(struct intel_dp *intel_dp)
> +{
> +	struct intel_connector *connector = intel_dp->attached_connector;
> +	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> +	struct intel_encoder *encoder = &intel_dig_port->base;
> +
> +	intel_dp->max_sink_lane_count = drm_dp_max_lane_count(intel_dp->dpcd);
> +
> +	switch (intel_dp->max_sink_lane_count) {
> +	case 1:
> +	case 2:
> +	case 4:
> +		return;
> +	}
> +
> +	drm_err(&dp_to_i915(intel_dp)->drm,
> +		"[CONNECTOR:%d:%s][ENCODER:%d:%s] Invalid DPCD max lane count (%d), using default\n",
> +		connector->base.base.id, connector->base.name,
> +		encoder->base.base.id, encoder->base.name,
> +		intel_dp->max_sink_lane_count);
> +
> +	intel_dp_set_default_max_sink_lane_count(intel_dp);
> +}
> +
>  /* Get length of rates array potentially limited by max_rate. */
>  static int intel_dp_rate_limit_len(const int *rates, int len, int max_rate)
>  {
> @@ -230,7 +259,7 @@ static int intel_dp_max_common_lane_count(struct intel_dp *intel_dp)
>  {
>  	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
>  	int source_max = dig_port->max_lanes;
> -	int sink_max = drm_dp_max_lane_count(intel_dp->dpcd);
> +	int sink_max = intel_dp->max_sink_lane_count;
>  	int fia_max = intel_tc_port_fia_max_lane_count(dig_port);
>  	int lttpr_max = drm_dp_lttpr_max_lane_count(intel_dp->lttpr_common_caps);
>  
> @@ -242,7 +271,15 @@ static int intel_dp_max_common_lane_count(struct intel_dp *intel_dp)
>  
>  int intel_dp_max_lane_count(struct intel_dp *intel_dp)
>  {
> -	return intel_dp->max_link_lane_count;
> +	switch (intel_dp->max_link_lane_count) {
> +	case 1:
> +	case 2:
> +	case 4:
> +		return intel_dp->max_link_lane_count;
> +	default:
> +		MISSING_CASE(intel_dp->max_link_lane_count);
> +		return 1;
> +	}
>  }

I guess this is just a second level sanity check. I was wondering it
gets confusing and people start thinking this can actually happen,
but I suppose the MISSING_CASE() should be indication enough that it
in fact should not happen.

Series looks sane to me:
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

BTW there's now some kms_bw thing in igt which seems to forcing
DP connectors on left and right, and thus triggering a bunch of 
WARNs.

>  
>  /*
> @@ -2600,6 +2637,7 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
>  		intel_dp->use_rate_select = true;
>  	else
>  		intel_dp_set_sink_rates(intel_dp);
> +	intel_dp_set_max_sink_lane_count(intel_dp);
>  
>  	intel_dp_set_common_rates(intel_dp);
>  	intel_dp_reset_max_link_params(intel_dp);
> @@ -2645,6 +2683,7 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  				 drm_dp_is_branch(intel_dp->dpcd));
>  
>  		intel_dp_set_sink_rates(intel_dp);
> +		intel_dp_set_max_sink_lane_count(intel_dp);
>  		intel_dp_set_common_rates(intel_dp);
>  	}
>  
> @@ -5011,6 +5050,7 @@ intel_dp_init_connector(struct intel_digital_port *dig_port,
>  
>  	intel_dp_set_source_rates(intel_dp);
>  	intel_dp_set_default_sink_rates(intel_dp);
> +	intel_dp_set_default_max_sink_lane_count(intel_dp);
>  	intel_dp_set_common_rates(intel_dp);
>  	intel_dp_reset_max_link_params(intel_dp);
>  
> -- 
> 2.27.0

-- 
Ville Syrjälä
Intel