[PATCH 06/20] drm/amd/display: Read eDP link settings on detection

[Bhawanpreet Lakha]

From: Anthony Koo <Anthony.Koo at amd.com>

[Why]
Unlike external DP panels, internal eDP does not perform
verify link caps because the panel connection is fixed.

So if GOP enabled the eDP at boot, we can retain its
trained link settings to optimize.

[How]
Read the lane count and link rate by reading this
information from DPCD 100h, 101h, 115h

Change-Id: If2f9588401731237e4dd7c587f4217bca4e5e08e
Signed-off-by: Anthony Koo <Anthony.Koo at amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr at amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet Lakha at amd.com>
---
 .../gpu/drm/amd/display/dc/core/dc_link_dp.c  | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
index acb4f829e042..ba7502f3d0eb 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
@@ -2587,6 +2587,9 @@ void detect_edp_sink_caps(struct dc_link *link)
 	uint32_t entry;
 	uint32_t link_rate_in_khz;
 	enum dc_link_rate link_rate = LINK_RATE_UNKNOWN;
+	union lane_count_set lane_count_set = { {0} };
+	uint8_t link_bw_set;
+	uint8_t link_rate_set;
 
 	retrieve_link_cap(link);
 	link->dpcd_caps.edp_supported_link_rates_count = 0;
@@ -2612,6 +2615,33 @@ void detect_edp_sink_caps(struct dc_link *link)
 		}
 	}
 	link->verified_link_cap = link->reported_link_cap;
+
+	// 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));
+	link->cur_link_settings.lane_count = lane_count_set.bits.LANE_COUNT_SET;
+
+	// Read DPCD 00100h to find if standard link rates are set
+	core_link_read_dpcd(link, DP_LINK_BW_SET,
+			&link_bw_set, sizeof(link_bw_set));
+
+	if (link_bw_set == 0) {
+		/* If standard link rates are not being used,
+		 * Read DPCD 00115h to find the link rate set used
+		 */
+		core_link_read_dpcd(link, DP_LINK_RATE_SET,
+				&link_rate_set, sizeof(link_rate_set));
+
+		if (link_rate_set < link->dpcd_caps.edp_supported_link_rates_count) {
+			link->cur_link_settings.link_rate =
+				link->dpcd_caps.edp_supported_link_rates[link_rate_set];
+			link->cur_link_settings.link_rate_set = link_rate_set;
+			link->cur_link_settings.use_link_rate_set = true;
+		}
+	} else {
+		link->cur_link_settings.link_rate = link_bw_set;
+		link->cur_link_settings.use_link_rate_set = false;
+	}
 }
 
 void dc_link_dp_enable_hpd(const struct dc_link *link)
-- 
2.17.1