drm/i915: WARN if a port should use VBT provided vswing tables

We don't parse the VBT vswing/preemphassis tables at all currently.
Let's WARN if a port wants to use them so we get a heads up that
whether we really need to implement this stuff or not. My
current stash contains no VBTs with this bit set.

v2: Move to print_ddi_port() (Jani)
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220916204132.10469-1-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

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

@@ -2676,6 +2676,14 @@ static void print_ddi_port(const struct intel_bios_encoder_data *devdata,
 		drm_dbg_kms(&i915->drm,
 			    "Port %c VBT DP max link rate: %d\n",
 			    port_name(port), dp_max_link_rate);
+
+	/*
+	 * FIXME need to implement support for VBT
+	 * vswing/preemph tables should this ever trigger.
+	 */
+	drm_WARN(&i915->drm, child->use_vbt_vswing,
+		 "Port %c asks to use VBT vswing/preemph tables\n",
+		 port_name(port));
 }
 
 static void parse_ddi_port(struct intel_bios_encoder_data *devdata)