drm/i915: Compute sink's max lane count/link BW at Hotplug

Sink's capabilities are advertised through DPCD registers and get
updated only on hotplug. So they should be computed only once in the
long pulse handler and saved off in intel_dp structure for the use
later. For this reason two new fields max_sink_lane_count and
max_sink_link_bw are added to intel_dp structure.

This also simplifies the fallback link rate/lane count logic
to handle link training failure. In that case, the max_sink_link_bw
and max_sink_lane_count can be reccomputed to match the fallback
values lowering the sink capabilities due to link train failure.

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1480984058-552-3-git-send-email-manasi.d.navare@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -156,7 +156,7 @@ static u8 intel_dp_max_lane_count(struct intel_dp *intel_dp)
 	u8 source_max, sink_max;
 
 	source_max = intel_dig_port->max_lanes;
-	sink_max = drm_dp_max_lane_count(intel_dp->dpcd);
+	sink_max = intel_dp->max_sink_lane_count;
 
 	return min(source_max, sink_max);
 }
@@ -213,7 +213,7 @@ intel_dp_sink_rates(struct intel_dp *intel_dp, const int **sink_rates)
 
 	*sink_rates = default_rates;
 
-	return (intel_dp_max_link_bw(intel_dp) >> 3) + 1;
+	return (intel_dp->max_sink_link_bw >> 3) + 1;
 }
 
 static int
@@ -4395,6 +4395,12 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
 		      yesno(intel_dp_source_supports_hbr2(intel_dp)),
 		      yesno(drm_dp_tps3_supported(intel_dp->dpcd)));
 
+	/* Set the max lane count for sink */
+	intel_dp->max_sink_lane_count = drm_dp_max_lane_count(intel_dp->dpcd);
+
+	/* Set the max link BW for sink */
+	intel_dp->max_sink_link_bw = intel_dp_max_link_bw(intel_dp);
+
 	intel_dp_print_rates(intel_dp);
 
 	intel_dp_read_desc(intel_dp);

drivers/gpu/drm/i915/intel_drv.h

@@ -906,6 +906,10 @@ struct intel_dp {
 	/* sink rates as reported by DP_SUPPORTED_LINK_RATES */
 	uint8_t num_sink_rates;
 	int sink_rates[DP_MAX_SUPPORTED_RATES];
+	/* Max lane count for the sink as per DPCD registers */
+	uint8_t max_sink_lane_count;
+	/* Max link BW for the sink as per DPCD registers */
+	int max_sink_link_bw;
 	/* sink or branch descriptor */
 	struct intel_dp_desc desc;
 	struct drm_dp_aux aux;