drm/amd/display: Don't perform rate toggle on DP2-capable FIXED_VS retimers

[WHY]
Only required if FIXED_VS retimer does not support DP2-capable.

[HOW]
Gate link rate toggle with DP 128b/132b LTTPR channel coding cap check.
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c

@@ -270,18 +270,20 @@ enum link_training_result dp_perform_fixed_vs_pe_training_sequence(
 
 	rate = get_dpcd_link_rate(&lt_settings->link_settings);
 
-	/* Vendor specific: Toggle link rate */
-	toggle_rate = (rate == 0x6) ? 0xA : 0x6;
+	if (!link->dpcd_caps.lttpr_caps.main_link_channel_coding.bits.DP_128b_132b_SUPPORTED) {
+		/* Vendor specific: Toggle link rate */
+		toggle_rate = (rate == 0x6) ? 0xA : 0x6;
 
-	if (link->vendor_specific_lttpr_link_rate_wa == rate || link->vendor_specific_lttpr_link_rate_wa == 0) {
-		core_link_write_dpcd(
-				link,
-				DP_LINK_BW_SET,
-				&toggle_rate,
-				1);
-	}
+		if (link->vendor_specific_lttpr_link_rate_wa == rate || link->vendor_specific_lttpr_link_rate_wa == 0) {
+			core_link_write_dpcd(
+					link,
+					DP_LINK_BW_SET,
+					&toggle_rate,
+					1);
+		}
 
-	link->vendor_specific_lttpr_link_rate_wa = rate;
+		link->vendor_specific_lttpr_link_rate_wa = rate;
+	}
 
 	core_link_write_dpcd(link, DP_LINK_BW_SET, &rate, 1);