During LT fallback, sometimes the sink/LTTPR reports a different lane count than what it reported previously. This can cause intel_dp->link.num_configs to have a different value than before, meaning that the previous link_rate/lane_config no longer exists, which results in the LT fallback failing prematurely and blank screen.
This issue was observed on an MTL RVP using an Asus DP2.1 monitor: [ 226.207376] AUX USBC2/DDI TC2/PHY TC2: 0xf0000 AUX -> (ret= 8) 20 1e 80 aa 04 00 01 03 [ 226.222334] AUX USBC2/DDI TC2/PHY TC2: 0x00000 AUX -> (ret= 15) 12 14 c4 81 01 00 03 c0 02 00 06 00 00 00 82 [ 226.236312] intel_dp_link_config_init 711 num_common_rates=5 num_common_lanes_configs=3 num_configs=15 [ 227.305515] AUX USBC2/DDI TC2/PHY TC2: 0xf0000 AUX -> (ret= 8) 20 1e 62 aa 01 00 01 00 [ 227.308100] AUX USBC2/DDI TC2/PHY TC2: 0x00000 AUX -> (ret= 15) 12 14 c4 81 01 00 03 c0 02 00 06 00 00 00 82 [ 227.315679] intel_dp_link_config_init 711 num_common_rates=5 num_common_lanes_configs=1 num_configs=5 Fix this by choosing the lowest config (link_rate/lane_count). Cc: Imre Deak <[email protected]> Cc: Jani Nikula <[email protected]> Signed-off-by: Charlton Lin <[email protected]> Signed-off-by: Khaled Almahallawy <[email protected]> --- drivers/gpu/drm/i915/display/intel_dp_link_training.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c index 26db4c49deec..7d2f1e540699 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c @@ -1199,6 +1199,15 @@ static bool reduce_link_params_in_bw_order(struct intel_dp *intel_dp, int i; i = intel_dp_link_config_index(intel_dp, crtc_state->port_clock, crtc_state->lane_count); + + if (i < 0) { + /* Old config is not located. Skip to the lowest*/ + intel_dp_link_config_get(intel_dp, 0, &link_rate, &lane_count); + *new_link_rate = link_rate; + *new_lane_count = lane_count; + return true; + } + for (i--; i >= 0; i--) { intel_dp_link_config_get(intel_dp, i, &link_rate, &lane_count); -- 2.43.0
