drm/amd/display: Refine aux transaction before retrieve caps

[Why]
LTTPR caps will read fail if aux channel is not active.

[How]
1.Perform 600 read upto 10 retry with 1ms delay in between.
2.If fail, return false and trigger another retry detection.
3.If pass, read LTTPR caps in retrieve link caps.
Reviewed-by: Jimmy Kizito <Jimmy.Kizito@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Lewis Huang <Lewis.Huang@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/core/dc_link_dp.c

@@ -5275,6 +5275,7 @@ static bool retrieve_link_cap(struct dc_link *link)
 	union dp_downstream_port_present ds_port = { 0 };
 	enum dc_status status = DC_ERROR_UNEXPECTED;
 	uint32_t read_dpcd_retry_cnt = 3;
+	uint32_t aux_channel_retry_cnt = 0;
 	int i;
 	struct dp_sink_hw_fw_revision dp_hw_fw_revision;
 	const uint32_t post_oui_delay = 30; // 30ms
@@ -5302,21 +5303,43 @@ static bool retrieve_link_cap(struct dc_link *link)
 		status = wa_try_to_wake_dprx(link, timeout_ms);
 	}
 
+	while (status != DC_OK && aux_channel_retry_cnt < 10) {
+		status = core_link_read_dpcd(link, DP_SET_POWER,
+				&dpcd_power_state, sizeof(dpcd_power_state));
+
+		/* Delay 1 ms if AUX CH is in power down state. Based on spec
+		 * section 2.3.1.2, if AUX CH may be powered down due to
+		 * write to DPCD 600h = 2. Sink AUX CH is monitoring differential
+		 * signal and may need up to 1 ms before being able to reply.
+		 */
+		if (status != DC_OK || dpcd_power_state == DP_SET_POWER_D3) {
+			udelay(1000);
+			aux_channel_retry_cnt++;
+		}
+	}
+
+	/* If aux channel is not active, return false and trigger another detect*/
+	if (status != DC_OK) {
+		dpcd_power_state = DP_SET_POWER_D0;
+		status = core_link_write_dpcd(
+				link,
+				DP_SET_POWER,
+				&dpcd_power_state,
+				sizeof(dpcd_power_state));
+
+		dpcd_power_state = DP_SET_POWER_D3;
+		status = core_link_write_dpcd(
+				link,
+				DP_SET_POWER,
+				&dpcd_power_state,
+				sizeof(dpcd_power_state));
+		return false;
+	}
+
 	is_lttpr_present = dp_retrieve_lttpr_cap(link);
 	/* Read DP tunneling information. */
 	status = dpcd_get_tunneling_device_data(link);
 
-	status = core_link_read_dpcd(link, DP_SET_POWER,
-			&dpcd_power_state, sizeof(dpcd_power_state));
-
-	/* Delay 1 ms if AUX CH is in power down state. Based on spec
-	 * section 2.3.1.2, if AUX CH may be powered down due to
-	 * write to DPCD 600h = 2. Sink AUX CH is monitoring differential
-	 * signal and may need up to 1 ms before being able to reply.
-	 */
-	if (status != DC_OK || dpcd_power_state == DP_SET_POWER_D3)
-		udelay(1000);
-
 	dpcd_set_source_specific_data(link);
 	/* Sink may need to configure internals based on vendor, so allow some
 	 * time before proceeding with possibly vendor specific transactions