drm/i915: Skip vswing programming for TBT

In thunderbolt mode the PHY is owned by the thunderbolt controller.
We are not supposed to touch it. So skip the vswing programming
as well (we already skipped the other steps not applicable to TBT).

Touching this stuff could supposedly interfere with the PHY
programming done by the thunderbolt controller.

Cc: stable@vger.kernel.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210128155948.13678-1-ville.syrjala@linux.intel.comReviewed-by: Imre Deak <imre.deak@intel.com>

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

@@ -2827,6 +2827,9 @@ static void icl_mg_phy_ddi_vswing_sequence(struct intel_encoder *encoder,
 	int n_entries, ln;
 	u32 val;
 
+	if (enc_to_dig_port(encoder)->tc_mode == TC_PORT_TBT_ALT)
+		return;
+
 	ddi_translations = icl_get_mg_buf_trans(encoder, crtc_state, &n_entries);
 
 	if (drm_WARN_ON_ONCE(&dev_priv->drm, !ddi_translations))
@@ -2962,6 +2965,9 @@ tgl_dkl_phy_ddi_vswing_sequence(struct intel_encoder *encoder,
 	u32 val, dpcnt_mask, dpcnt_val;
 	int n_entries, ln;
 
+	if (enc_to_dig_port(encoder)->tc_mode == TC_PORT_TBT_ALT)
+		return;
+
 	ddi_translations = tgl_get_dkl_buf_trans(encoder, crtc_state, &n_entries);
 
 	if (drm_WARN_ON_ONCE(&dev_priv->drm, !ddi_translations))