drm/amd/display: Use absolute time stamp to follow the eDP T7 spec requirement

[Why]:
According to eDP spec, max T7 delay should be 50 ms. Current code uses 300
retry counters may not be accurate enough for different panels.

[How]:
Use absolute time stamp to achive accurate delay.
Signed-off-by: Dale Zhao <dale.zhao@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -173,15 +173,20 @@ bool edp_receiver_ready_T9(struct dc_link *link)
 }
 bool edp_receiver_ready_T7(struct dc_link *link)
 {
-	unsigned int tries = 0;
 	unsigned char sinkstatus = 0;
 	unsigned char edpRev = 0;
 	enum dc_status result = DC_OK;
 
+	/* use absolute time stamp to constrain max T7*/
+	unsigned long long enter_timestamp = 0;
+	unsigned long long finish_timestamp = 0;
+	unsigned long long time_taken_in_ns = 0;
+
 	result = core_link_read_dpcd(link, DP_EDP_DPCD_REV, &edpRev, sizeof(edpRev));
 	if (result == DC_OK && edpRev < DP_EDP_12)
 		return true;
 	/* start from eDP version 1.2, SINK_STAUS indicate the sink is ready.*/
+	enter_timestamp = dm_get_timestamp(link->ctx);
 	do {
 		sinkstatus = 0;
 		result = core_link_read_dpcd(link, DP_SINK_STATUS, &sinkstatus, sizeof(sinkstatus));
@@ -189,8 +194,10 @@ bool edp_receiver_ready_T7(struct dc_link *link)
 			break;
 		if (result != DC_OK)
 			break;
-		udelay(25); //MAx T7 is 50ms
-	} while (++tries < 300);
+		udelay(25);
+		finish_timestamp = dm_get_timestamp(link->ctx);
+		time_taken_in_ns = dm_get_elapse_time_in_ns(link->ctx, finish_timestamp, enter_timestamp);
+	} while (time_taken_in_ns < 50 * 1000000); //MAx T7 is 50ms
 
 	if (link->local_sink->edid_caps.panel_patch.extra_t7_ms > 0)
 		udelay(link->local_sink->edid_caps.panel_patch.extra_t7_ms * 1000);