drm/amd/display: Improve robustness of FIXED_VS link training at DP1 rates

[WHY]
New sequence for transparent mode DP1.x link training was provided by LTTPR
vendor

[HOW]
Implement new FIXED_VS sequence, increase LT retry count to minimize
any potential intermittent lightup failures
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dc.h

@@ -405,6 +405,7 @@ struct dc_config {
 	bool force_bios_enable_lttpr;
 	uint8_t force_bios_fixed_vs;
 	int sdpif_request_limit_words_per_umc;
+	bool use_old_fixed_vs_sequence;
 	bool disable_subvp_drr;
 };
 

drivers/gpu/drm/amd/display/dc/dcn31/dcn31_resource.c

@@ -1965,6 +1965,8 @@ static bool dcn31_resource_construct(
 	dc->caps.color.mpc.ogam_rom_caps.hlg = 0;
 	dc->caps.color.mpc.ocsc = 1;
 
+	dc->config.use_old_fixed_vs_sequence = true;
+
 	/* Use pipe context based otg sync logic */
 	dc->config.use_pipe_ctx_sync_logic = true;
 

drivers/gpu/drm/amd/display/dc/link/link_dpms.c

@@ -2035,6 +2035,12 @@ static enum dc_status enable_link_dp(struct dc_state *state,
 	uint32_t post_oui_delay = 30; // 30ms
 	/* Reduce link bandwidth between failed link training attempts. */
 	bool do_fallback = false;
+	int lt_attempts = LINK_TRAINING_ATTEMPTS;
+
+	// Increase retry count if attempting DP1.x on FIXED_VS link
+	if ((link->chip_caps & EXT_DISPLAY_PATH_CAPS__DP_FIXED_VS_EN) &&
+			link_dp_get_encoding_format(link_settings) == DP_8b_10b_ENCODING)
+		lt_attempts = 10;
 
 	// check for seamless boot
 	for (i = 0; i < state->stream_count; i++) {
@@ -2099,7 +2105,7 @@ static enum dc_status enable_link_dp(struct dc_state *state,
 
 	if (perform_link_training_with_retries(link_settings,
 					       skip_video_pattern,
-					       LINK_TRAINING_ATTEMPTS,
+					       lt_attempts,
 					       pipe_ctx,
 					       pipe_ctx->stream->signal,
 					       do_fallback)) {

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

@@ -1496,6 +1496,9 @@ enum link_training_result dp_perform_link_training(
 	 * Non-LT AUX transactions inside training mode.
 	 */
 	if ((link->chip_caps & EXT_DISPLAY_PATH_CAPS__DP_FIXED_VS_EN) && encoding == DP_8b_10b_ENCODING)
+		if (link->dc->config.use_old_fixed_vs_sequence)
+			status = dp_perform_fixed_vs_pe_training_sequence_legacy(link, link_res, &lt_settings);
+		else
 			status = dp_perform_fixed_vs_pe_training_sequence(link, link_res, &lt_settings);
 	else if (encoding == DP_8b_10b_ENCODING)
 		status = dp_perform_8b_10b_link_training(link, link_res, &lt_settings);

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

@@ -28,6 +28,11 @@
 #define __DC_LINK_DP_FIXED_VS_PE_RETIMER_H__
 #include "link_dp_training.h"
 
+enum link_training_result dp_perform_fixed_vs_pe_training_sequence_legacy(
+	struct dc_link *link,
+	const struct link_resource *link_res,
+	struct link_training_settings *lt_settings);
+
 enum link_training_result dp_perform_fixed_vs_pe_training_sequence(
 	struct dc_link *link,
 	const struct link_resource *link_res,