drm/amd/display: fix issue with eDP not detected on driver load

[Why]
HPD not going to be high if Panel VDD is off
And all AUX transaction will fail :(

[How]
1. Power on VDD before attempting detection if it isn't already on
2. Improve the robustness by having a retry mechanism on the
first DPCD read after VDD on. If a particular board always holds
HPD high incorrectly, the AUX access may fail, so we can retry
in those scenarios. This change would only improve logic
since it prevents AUX failure leading to bad resolution on internal
panel.
3. We should never need to re-detect internal panel, so logic
is re-arranged a bit to skip earlier.
Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -217,8 +217,11 @@ bool dc_link_detect_sink(struct dc_link *link, enum dc_connection_type *type)
 		return true;
 	}
 
-	if (link->connector_signal == SIGNAL_TYPE_EDP)
+	if (link->connector_signal == SIGNAL_TYPE_EDP) {
+		/*in case it is not on*/
+		link->dc->hwss.edp_power_control(link, true);
 		link->dc->hwss.edp_wait_for_hpd_ready(link, true);
+	}
 
 	/* todo: may need to lock gpio access */
 	hpd_pin = get_hpd_gpio(link->ctx->dc_bios, link->link_id, link->ctx->gpio_service);
@@ -520,11 +523,31 @@ static void read_edp_current_link_settings_on_detect(struct dc_link *link)
 	union lane_count_set lane_count_set = { {0} };
 	uint8_t link_bw_set;
 	uint8_t link_rate_set;
+	uint32_t read_dpcd_retry_cnt = 10;
+	enum dc_status status = DC_ERROR_UNEXPECTED;
+	int i;
 
 	// Read DPCD 00101h to find out the number of lanes currently set
-	core_link_read_dpcd(link, DP_LANE_COUNT_SET,
-			&lane_count_set.raw, sizeof(lane_count_set));
+	for (i = 0; i < read_dpcd_retry_cnt; i++) {
+		status = core_link_read_dpcd(
+				link,
+				DP_LANE_COUNT_SET,
+				&lane_count_set.raw,
+				sizeof(lane_count_set));
+		/* First DPCD read after VDD ON can fail if the particular board
+		 * does not have HPD pin wired correctly. So if DPCD read fails,
+		 * which it should never happen, retry a few times. Target worst
+		 * case scenario of 80 ms.
+		 */
+		if (status == DC_OK) {
 			link->cur_link_settings.lane_count = lane_count_set.bits.LANE_COUNT_SET;
+			break;
+		}
+
+		udelay(8000);
+	}
+
+	ASSERT(status == DC_OK);
 
 	// Read DPCD 00100h to find if standard link rates are set
 	core_link_read_dpcd(link, DP_LINK_BW_SET,
@@ -678,6 +701,11 @@ bool dc_link_detect(struct dc_link *link, enum dc_detect_reason reason)
 	if (dc_is_virtual_signal(link->connector_signal))
 		return false;
 
+	if ((link->connector_signal == SIGNAL_TYPE_LVDS ||
+			link->connector_signal == SIGNAL_TYPE_EDP) &&
+			link->local_sink)
+		return true;
+
 	if (false == dc_link_detect_sink(link, &new_connection_type)) {
 		BREAK_TO_DEBUGGER();
 		return false;
@@ -688,14 +716,8 @@ bool dc_link_detect(struct dc_link *link, enum dc_detect_reason reason)
 		 * up to date, especially if link was powered on by GOP.
 		 */
 		read_edp_current_link_settings_on_detect(link);
-		if (link->local_sink)
-			return true;
 	}
 
-	if (link->connector_signal == SIGNAL_TYPE_LVDS &&
-			link->local_sink)
-		return true;
-
 	prev_sink = link->local_sink;
 	if (prev_sink != NULL) {
 		dc_sink_retain(prev_sink);