drm/amd/display: Enumerate LTTPR modes

[WHY]
There are three possible modes for LTTPR:
- Non-LTTPR mode, where AUX timeout is 400 us and no per-hop link
training is done
- LTTPR Transparent mode, where AUX timeout is 3200 us and no per-hop
link training is done
- LTTPR Non-Transparent mode, where AUX timeout is 3200 us and per-hop
link training is done

[HOW]
Use an enum instead of a bool to track LTTPR state; modify comparisons
accordingly.
Signed-off-by: Wesley Chalmers <Wesley.Chalmers@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c

@@ -284,7 +284,7 @@ static uint8_t dc_dp_initialize_scrambling_data_symbols(
 
 static inline bool is_repeater(struct dc_link *link, uint32_t offset)
 {
-	return (link->lttpr_non_transparent_mode && offset != 0);
+	return (link->lttpr_mode == LTTPR_MODE_NON_TRANSPARENT) && (offset != 0);
 }
 
 static void dpcd_set_lt_pattern_and_lane_settings(
@@ -1072,7 +1072,7 @@ static enum link_training_result perform_clock_recovery_sequence(
 		/* 3. wait receiver to lock-on*/
 		wait_time_microsec = lt_settings->cr_pattern_time;
 
-		if (link->lttpr_non_transparent_mode)
+		if (link->lttpr_mode == LTTPR_MODE_NON_TRANSPARENT)
 			wait_time_microsec = TRAINING_AUX_RD_INTERVAL;
 
 		wait_for_training_aux_rd_interval(
@@ -1326,7 +1326,17 @@ static uint8_t convert_to_count(uint8_t lttpr_repeater_count)
 	return 0; // invalid value
 }
 
-static void configure_lttpr_mode(struct dc_link *link)
+static void configure_lttpr_mode_transparent(struct dc_link *link)
+{
+	uint8_t repeater_mode = DP_PHY_REPEATER_MODE_TRANSPARENT;
+
+	core_link_write_dpcd(link,
+			DP_PHY_REPEATER_MODE,
+			(uint8_t *)&repeater_mode,
+			sizeof(repeater_mode));
+}
+
+static void configure_lttpr_mode_non_transparent(struct dc_link *link)
 {
 	/* aux timeout is already set to extended */
 	/* RESET/SET lttpr mode to enable non transparent mode */
@@ -1346,7 +1356,7 @@ static void configure_lttpr_mode(struct dc_link *link)
 		link->dpcd_caps.lttpr_caps.mode = repeater_mode;
 	}
 
-	if (link->lttpr_non_transparent_mode) {
+	if (link->lttpr_mode == LTTPR_MODE_NON_TRANSPARENT) {
 
 		DC_LOG_HW_LINK_TRAINING("%s\n Set LTTPR to Non Transparent Mode\n", __func__);
 
@@ -1562,8 +1572,10 @@ enum link_training_result dc_link_dp_perform_link_training(
 			&lt_settings);
 
 	/* Configure lttpr mode */
-	if (link->lttpr_non_transparent_mode)
-		configure_lttpr_mode(link);
+	if (link->lttpr_mode == LTTPR_MODE_NON_TRANSPARENT)
+		configure_lttpr_mode_non_transparent(link);
+	else if (link->lttpr_mode == LTTPR_MODE_TRANSPARENT)
+		configure_lttpr_mode_transparent(link);
 
 	if (link->ctx->dc->work_arounds.lt_early_cr_pattern)
 		start_clock_recovery_pattern_early(link, &lt_settings, DPRX);
@@ -1578,7 +1590,7 @@ enum link_training_result dc_link_dp_perform_link_training(
 
 	dp_set_fec_ready(link, fec_enable);
 
-	if (link->lttpr_non_transparent_mode) {
+	if (link->lttpr_mode == LTTPR_MODE_NON_TRANSPARENT) {
 
 		/* 2. perform link training (set link training done
 		 *  to false is done as well)
@@ -1899,7 +1911,7 @@ static struct dc_link_settings get_max_link_cap(struct dc_link *link)
 	 * account for lttpr repeaters cap
 	 * notes: repeaters do not snoop in the DPRX Capabilities addresses (3.6.3).
 	 */
-	if (link->lttpr_non_transparent_mode) {
+	if (link->lttpr_mode == LTTPR_MODE_NON_TRANSPARENT) {
 		if (link->dpcd_caps.lttpr_caps.max_lane_count < max_link_cap.lane_count)
 			max_link_cap.lane_count = link->dpcd_caps.lttpr_caps.max_lane_count;
 
@@ -2057,7 +2069,7 @@ bool dp_verify_link_cap(
 	max_link_cap = get_max_link_cap(link);
 
 	/* Grant extended timeout request */
-	if (link->lttpr_non_transparent_mode && link->dpcd_caps.lttpr_caps.max_ext_timeout > 0) {
+	if ((link->lttpr_mode == LTTPR_MODE_NON_TRANSPARENT) && (link->dpcd_caps.lttpr_caps.max_ext_timeout > 0)) {
 		uint8_t grant = link->dpcd_caps.lttpr_caps.max_ext_timeout & 0x80;
 
 		core_link_write_dpcd(link, DP_PHY_REPEATER_EXTENDED_WAIT_TIMEOUT, &grant, sizeof(grant));
@@ -3529,7 +3541,8 @@ static bool retrieve_link_cap(struct dc_link *link)
 	}
 
 	/* decide lttpr non transparent mode */
-	link->lttpr_non_transparent_mode = is_lttpr_present;
+	/*This is a temporary placeholder for LTTPR logic. More comprehensive logic will be added in a future change*/
+	link->lttpr_mode = is_lttpr_present ? LTTPR_MODE_NON_TRANSPARENT : LTTPR_MODE_NON_LTTPR;
 
 	if (!is_lttpr_present)
 		dc_link_aux_try_to_configure_timeout(link->ddc, LINK_AUX_DEFAULT_TIMEOUT_PERIOD);

drivers/gpu/drm/amd/display/dc/core/dc_link_hwss.c

@@ -302,7 +302,7 @@ void dp_set_hw_lane_settings(
 {
 	struct link_encoder *encoder = link->link_enc;
 
-	if (link->lttpr_non_transparent_mode && !is_immediate_downstream(link, offset))
+	if ((link->lttpr_mode == LTTPR_MODE_NON_TRANSPARENT) && !is_immediate_downstream(link, offset))
 		return;
 
 	/* call Encoder to set lane settings */

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

@@ -35,6 +35,13 @@ enum dc_link_fec_state {
 	dc_link_fec_ready,
 	dc_link_fec_enabled
 };
+
+enum lttpr_mode {
+	LTTPR_MODE_NON_LTTPR,
+	LTTPR_MODE_TRANSPARENT,
+	LTTPR_MODE_NON_TRANSPARENT,
+};
+
 struct dc_link_status {
 	bool link_active;
 	struct dpcd_caps *dpcd_caps;
@@ -100,7 +107,7 @@ struct dc_link {
 	bool link_state_valid;
 	bool aux_access_disabled;
 	bool sync_lt_in_progress;
-	bool lttpr_non_transparent_mode;
+	enum lttpr_mode lttpr_mode;
 	bool is_internal_display;
 
 	/* TODO: Rename. Flag an endpoint as having a programmable mapping to a