From 47c2790ad69d1f072e7e26dc16bb91e99dd4c946 Mon Sep 17 00:00:00 2001 From: Michael Strauss Date: Wed, 31 Aug 2022 15:10:43 -0400 Subject: [PATCH] drm/amd/display: Assume an LTTPR is always present on fixed_vs links [WHY] LTTPRs can in very rare instsances fail to increment DPCD LTTPR count. This results in aux-i LTTPR requests to be sent to the wrong DPCD address, which causes link training failure. [HOW] Override internal repeater count if fixed_vs flag is set for a given link Reviewed-by: George Shen Acked-by: Wayne Lin Signed-off-by: Michael Strauss Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 8 ++++++++ 1 file changed, 8 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 e2413d2..2aa91cd 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 @@ -5133,6 +5133,14 @@ bool dp_retrieve_lttpr_cap(struct dc_link *link) lttpr_dpcd_data[DP_PHY_REPEATER_128B132B_RATES - DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV]; + /* If this chip cap is set, at least one retimer must exist in the chain + * Override count to 1 if we receive a known bad count (0 or an invalid value) */ + if (link->chip_caps & EXT_DISPLAY_PATH_CAPS__DP_FIXED_VS_EN && + (dp_convert_to_count(link->dpcd_caps.lttpr_caps.phy_repeater_cnt) == 0)) { + ASSERT(0); + link->dpcd_caps.lttpr_caps.phy_repeater_cnt = 0x80; + } + /* Attempt to train in LTTPR transparent mode if repeater count exceeds 8. */ is_lttpr_present = (link->dpcd_caps.lttpr_caps.max_lane_count > 0 && link->dpcd_caps.lttpr_caps.max_lane_count <= 4 && -- 2.7.4