drm/amd/display: Work around bad DPCD state on link loss

[Why]
This display doesn't properly indicate link loss through DPCD bits such
as CR_DONE / CHANNEL_EQ_DONE / SYMBOL_LOCKED / INTERLANE_ALIGN_DONE,
which all remain set.

In addition, DPCD200Eh doesn't match the value of DPCD204h in all cases.

For these reasons, we can miss re-training the link, since we don't
properly detect link loss with this display.

[Why]
Add display-specific workaround to read DPCD204h, so that we can detect
link loss based on 128b132b-specific status bits in this register.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Ilya Bakoulin <ilya.bakoulin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Ilya Bakoulin

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

@@ -1525,6 +1525,7 @@ struct dc_link {
 		bool dpia_forced_tbt3_mode;
 		bool dongle_mode_timing_override;
 		bool blank_stream_on_ocs_change;
+		bool read_dpcd204h_on_irq_hpd;
 	} wa_flags;
 	struct link_mst_stream_allocation_table mst_stream_alloc_table;
 

drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_irq_handler.c

@@ -208,6 +208,25 @@ void dp_handle_link_loss(struct dc_link *link)
 	}
 }
 
+static void read_dpcd204h_on_irq_hpd(struct dc_link *link, union hpd_irq_data *irq_data)
+{
+	enum dc_status retval;
+	union lane_align_status_updated dpcd_lane_status_updated;
+
+	retval = core_link_read_dpcd(
+			link,
+			DP_LANE_ALIGN_STATUS_UPDATED,
+			&dpcd_lane_status_updated.raw,
+			sizeof(union lane_align_status_updated));
+
+	if (retval == DC_OK) {
+		irq_data->bytes.lane_status_updated.bits.EQ_INTERLANE_ALIGN_DONE_128b_132b =
+				dpcd_lane_status_updated.bits.EQ_INTERLANE_ALIGN_DONE_128b_132b;
+		irq_data->bytes.lane_status_updated.bits.CDS_INTERLANE_ALIGN_DONE_128b_132b =
+				dpcd_lane_status_updated.bits.CDS_INTERLANE_ALIGN_DONE_128b_132b;
+	}
+}
+
 enum dc_status dp_read_hpd_rx_irq_data(
 	struct dc_link *link,
 	union hpd_irq_data *irq_data)
@@ -249,6 +268,13 @@ enum dc_status dp_read_hpd_rx_irq_data(
 		irq_data->bytes.lane23_status.raw = tmp[DP_LANE2_3_STATUS_ESI - DP_SINK_COUNT_ESI];
 		irq_data->bytes.lane_status_updated.raw = tmp[DP_LANE_ALIGN_STATUS_UPDATED_ESI - DP_SINK_COUNT_ESI];
 		irq_data->bytes.sink_status.raw = tmp[DP_SINK_STATUS_ESI - DP_SINK_COUNT_ESI];
+
+		/*
+		 * This display doesn't have correct values in DPCD200Eh.
+		 * Read and check DPCD204h instead.
+		 */
+		if (link->wa_flags.read_dpcd204h_on_irq_hpd)
+			read_dpcd204h_on_irq_hpd(link, irq_data);
 	}
 
 	return retval;