drm/amd/display: Add work around for AUX failure on wake.

[Why]
When waking from low-power states, a DP sink may remain unresponsive to
AUX transactions.

[How]
Try to toggle DPCD SET_POWER register repeatedly (up to a maximum
timeout value) until DP sink becomes responsive.

Reviewed-by: Mustapha Ghaddar <Mustapha.Ghaddar@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Jimmy Kizito <Jimmy.Kizito@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

@@ -5216,6 +5216,62 @@ static void retrieve_cable_id(struct dc_link *link)
 				&link->dpcd_caps.cable_id, &usbc_cable_id);
 }
 
+/* DPRX may take some time to respond to AUX messages after HPD asserted.
+ * If AUX read unsuccessful, try to wake unresponsive DPRX by toggling DPCD SET_POWER (0x600).
+ */
+static enum dc_status wa_try_to_wake_dprx(struct dc_link *link, uint64_t timeout_ms)
+{
+	enum dc_status status = DC_ERROR_UNEXPECTED;
+	uint8_t dpcd_data = 0;
+	uint64_t start_ts = 0;
+	uint64_t current_ts = 0;
+	uint64_t time_taken_ms = 0;
+	enum dc_connection_type type = dc_connection_none;
+
+	status = core_link_read_dpcd(
+			link,
+			DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV,
+			&dpcd_data,
+			sizeof(dpcd_data));
+
+	if (status != DC_OK) {
+		DC_LOG_WARNING("%s: Read DPCD LTTPR_CAP failed - try to toggle DPCD SET_POWER for %lld ms.",
+				__func__,
+				timeout_ms);
+		start_ts = dm_get_timestamp(link->ctx);
+
+		do {
+			if (!dc_link_detect_sink(link, &type) || type == dc_connection_none)
+				break;
+
+			dpcd_data = DP_SET_POWER_D3;
+			status = core_link_write_dpcd(
+					link,
+					DP_SET_POWER,
+					&dpcd_data,
+					sizeof(dpcd_data));
+
+			dpcd_data = DP_SET_POWER_D0;
+			status = core_link_write_dpcd(
+					link,
+					DP_SET_POWER,
+					&dpcd_data,
+					sizeof(dpcd_data));
+
+			current_ts = dm_get_timestamp(link->ctx);
+			time_taken_ms = div_u64(dm_get_elapse_time_in_ns(link->ctx, current_ts, start_ts), 1000000);
+		} while (status != DC_OK && time_taken_ms < timeout_ms);
+
+		DC_LOG_WARNING("%s: DPCD SET_POWER %s after %lld ms%s",
+				__func__,
+				(status == DC_OK) ? "succeeded" : "failed",
+				time_taken_ms,
+				(type == dc_connection_none) ? ". Unplugged." : ".");
+	}
+
+	return status;
+}
+
 static bool retrieve_link_cap(struct dc_link *link)
 {
 	/* DP_ADAPTER_CAP - DP_DPCD_REV + 1 == 16 and also DP_DSC_BITS_PER_PIXEL_INC - DP_DSC_SUPPORT + 1 == 16,
@@ -5251,6 +5307,9 @@ static bool retrieve_link_cap(struct dc_link *link)
 	dc_link_aux_try_to_configure_timeout(link->ddc,
 			LINK_AUX_DEFAULT_LTTPR_TIMEOUT_PERIOD);
 
+	/* Try to ensure AUX channel active before proceeding. */
+	status = wa_try_to_wake_dprx(link, LINK_AUX_WAKE_TIMEOUT_MS);
+
 	is_lttpr_present = dp_retrieve_lttpr_cap(link);
 	/* Read DP tunneling information. */
 	status = dpcd_get_tunneling_device_data(link);

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

@@ -33,6 +33,7 @@
 #define MAX_MTP_SLOT_COUNT 64
 #define DP_REPEATER_CONFIGURATION_AND_STATUS_SIZE 0x50
 #define TRAINING_AUX_RD_INTERVAL 100 //us
+#define LINK_AUX_WAKE_TIMEOUT_MS 1500 // Timeout when trying to wake unresponsive DPRX.
 
 struct dc_link;
 struct dc_stream_state;