drm/i915: WARN about invalid lane reversal in TBT-alt/DP-alt modes

Lane reversal happens only in the FIA module for TBT-alt/DP-alt mode, so
WARN if lane reversal is attempted at a different level. See the
BSpec DDI_BUF_CTL register description.

Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190628143635.22066-24-imre.deak@intel.com

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

@@ -3604,6 +3604,8 @@ static void intel_ddi_set_fia_lane_count(struct intel_encoder *encoder,
 	u32 val = I915_READ(PORT_TX_DFLEXDPMLE1);
 	bool lane_reversal = dig_port->saved_port_bits & DDI_BUF_PORT_REVERSAL;
 
+	WARN_ON(lane_reversal && dig_port->tc_mode != TC_PORT_LEGACY);
+
 	val &= ~DFLEXDPMLE1_DPMLETC_MASK(tc_port);
 	switch (pipe_config->lane_count) {
 	case 1: