drm/i915/dp: Limit SST link rate to <=8.1Gbps

Limit the link rate to HBR3 or below (<=8.1Gbps) in SST mode.
UHBR (10Gbps+) link rates require 128b/132b channel encoding
which we have not yet hooked up into the SST/no-sideband codepaths.

Cc: stable@vger.kernel.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240208154552.14545-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit 6061811)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Author: vsyrjala

drivers/gpu/drm/i915/display/intel_dp.c

@@ -2355,6 +2355,9 @@ intel_dp_compute_config_limits(struct intel_dp *intel_dp,
 	limits->min_rate = intel_dp_common_rate(intel_dp, 0);
 	limits->max_rate = intel_dp_max_link_rate(intel_dp);
 
+	/* FIXME 128b/132b SST support missing */
+	limits->max_rate = min(limits->max_rate, 810000);
+
 	limits->min_lane_count = 1;
 	limits->max_lane_count = intel_dp_max_lane_count(intel_dp);