drm/i915/dp: centralize max source rate conditions more

Turn intel_dp_source_supports_hbr2() into a simple helper to query the
pre-filled source rates array, and move the conditions about which
platforms support which rates to the single point of truth in
intel_dp_set_source_rates().

This also reduces the code paths you have to think about in the source
rates initialization in intel_dp_set_source_rates(), making it easier to
grasp.

Cc: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171009092959.29021-2-jani.nikula@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -254,15 +254,15 @@ intel_dp_set_source_rates(struct intel_dp *intel_dp)
 	} else if (IS_GEN9_BC(dev_priv)) {
 		source_rates = skl_rates;
 		size = ARRAY_SIZE(skl_rates);
-	} else {
+	} else if ((IS_HASWELL(dev_priv) && !IS_HSW_ULX(dev_priv)) ||
+		   IS_BROADWELL(dev_priv)) {
 		source_rates = default_rates;
 		size = ARRAY_SIZE(default_rates);
+	} else {
+		source_rates = default_rates;
+		size = ARRAY_SIZE(default_rates) - 1;
 	}
 
-	/* This depends on the fact that 5.4 is last value in the array */
-	if (!intel_dp_source_supports_hbr2(intel_dp))
-		size--;
-
 	intel_dp->source_rates = source_rates;
 	intel_dp->num_source_rates = size;
 }
@@ -1482,14 +1482,9 @@ intel_dp_aux_init(struct intel_dp *intel_dp)
 
 bool intel_dp_source_supports_hbr2(struct intel_dp *intel_dp)
 {
-	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
-	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
+	int max_rate = intel_dp->source_rates[intel_dp->num_source_rates - 1];
 
-	if ((IS_HASWELL(dev_priv) && !IS_HSW_ULX(dev_priv)) ||
-	    IS_BROADWELL(dev_priv) || (INTEL_GEN(dev_priv) >= 9))
-		return true;
-	else
-		return false;
+	return max_rate >= 540000;
 }
 
 static void