[PATCH 2/2] drm/amd/display: Add dp_skip_rbr flag for NUTMEG

["Timur Kristóf" <timur.kristof@gmail.com>]

No functional changes. Just clean up a conceptual mismatch.

Based on feedback on the NUTMEG code in DC, the
preferred_link_setting is meant to force the DP link to a
specific setting, meaning both the link rate and lane count
should be locked to an exact value. What NUTMEG needs is
a lower bound on the link rate, which is not the same concept.

Implement this as a HW workaround flag instead.

Suggested-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
---
 drivers/gpu/drm/amd/display/dc/dc.h                         | 2 ++
 drivers/gpu/drm/amd/display/dc/link/link_detection.c        | 2 +-
 .../drm/amd/display/dc/link/protocols/link_dp_capability.c  | 6 +++---
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dc.h b/drivers/gpu/drm/amd/display/dc/dc.h
index 75f59ca927ffe..3fb97860722df 100644
--- a/drivers/gpu/drm/amd/display/dc/dc.h
+++ b/drivers/gpu/drm/amd/display/dc/dc.h
@@ -1731,6 +1731,8 @@ struct dc_scratch_space {
 		bool dp_skip_DID2;
 		bool dp_skip_reset_segment;
 		bool dp_skip_fs_144hz;
+		/* Some DP bridges don't work with RBR and must use HBR. */
+		bool dp_skip_rbr;
 		bool dp_mot_reset_segment;
 		/* Some USB4 docks do not handle turning off MST DSC once it has been enabled. */
 		bool dpia_mst_dsc_always_on;
diff --git a/drivers/gpu/drm/amd/display/dc/link/link_detection.c b/drivers/gpu/drm/amd/display/dc/link/link_detection.c
index 1ac6a22fecfee..9f4e90493fed5 100644
--- a/drivers/gpu/drm/amd/display/dc/link/link_detection.c
+++ b/drivers/gpu/drm/amd/display/dc/link/link_detection.c
@@ -621,7 +621,7 @@ static bool detect_dp(struct dc_link *link,
 		link->dpcd_caps.sink_count.bits.SINK_COUNT = 1;
 		/* NUTMEG requires that we use HBR, doesn't work with RBR. */
 		if (link->dpcd_caps.branch_dev_id == DP_BRANCH_DEVICE_ID_00001A)
-			link->preferred_link_setting.link_rate = LINK_RATE_HIGH;
+			link->wa_flags.dp_skip_rbr = true;
 	}
 
 	return true;
diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c
index f44c13300a59c..708dd6f336d8c 100644
--- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c
+++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c
@@ -750,9 +750,9 @@ static bool decide_dp_link_settings(struct dc_link *link, struct dc_link_setting
 	if (req_bw > dp_link_bandwidth_kbps(link, &link->verified_link_cap))
 		return false;
 
-	if (link->preferred_link_setting.link_rate != LINK_RATE_UNKNOWN) {
-		initial_link_setting.link_rate = link->preferred_link_setting.link_rate;
-		current_link_setting.link_rate = link->preferred_link_setting.link_rate;
+	if (link->wa_flags.dp_skip_rbr) {
+		initial_link_setting.link_rate = LINK_RATE_HIGH;
+		current_link_setting.link_rate = LINK_RATE_HIGH;
 	}
 
 	/* search for the minimum link setting that:
-- 
2.53.0