From 583ad88871b38dc39f05a316dcde909e444b09a6 Mon Sep 17 00:00:00 2001 From: Ilya Date: Mon, 7 Feb 2022 17:39:10 -0500 Subject: [PATCH] drm/amd/display: Fix possible infinite loop in DP LT fallback [Why] It's possible for some fallback scenarios to result in infinite looping during link training. [How] This change modifies DP LT fallback behavior to more closely match the DP standard. Keep track of the link rate during the EQ_FAIL fallback, and use it as the maximum link rate for the CR sequence. Reviewed-by: Wenjing Liu Tested-by: Daniel Wheeler Signed-off-by: Ilya Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 106 +++++++++++------------ 1 file changed, 49 insertions(+), 57 deletions(-) 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 3c95232..03eedff 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 @@ -114,8 +114,8 @@ static const struct dc_link_settings fail_safe_link_settings = { static bool decide_fallback_link_setting( struct dc_link *link, - struct dc_link_settings initial_link_settings, - struct dc_link_settings *current_link_setting, + struct dc_link_settings *max, + struct dc_link_settings *cur, enum link_training_result training_result); static void maximize_lane_settings(const struct link_training_settings *lt_settings, struct dc_lane_settings lane_settings[LANE_COUNT_DP_MAX]); @@ -2784,6 +2784,7 @@ bool perform_link_training_with_retries( enum dp_panel_mode panel_mode = dp_get_panel_mode(link); enum link_training_result status = LINK_TRAINING_CR_FAIL_LANE0; struct dc_link_settings cur_link_settings = *link_setting; + struct dc_link_settings max_link_settings = *link_setting; const struct link_hwss *link_hwss = get_link_hwss(link, &pipe_ctx->link_res); int fail_count = 0; bool is_link_bw_low = false; /* link bandwidth < stream bandwidth */ @@ -2793,7 +2794,6 @@ bool perform_link_training_with_retries( dp_trace_commit_lt_init(link); - if (dp_get_link_encoding_format(&cur_link_settings) == DP_8b_10b_ENCODING) /* We need to do this before the link training to ensure the idle * pattern in SST mode will be sent right after the link training @@ -2909,19 +2909,15 @@ bool perform_link_training_with_retries( uint32_t req_bw; uint32_t link_bw; - decide_fallback_link_setting(link, *link_setting, &cur_link_settings, status); - /* Flag if reduced link bandwidth no longer meets stream requirements or fallen back to - * minimum link bandwidth. + decide_fallback_link_setting(link, &max_link_settings, + &cur_link_settings, status); + /* Fail link training if reduced link bandwidth no longer meets + * stream requirements. */ req_bw = dc_bandwidth_in_kbps_from_timing(&stream->timing); link_bw = dc_link_bandwidth_kbps(link, &cur_link_settings); - is_link_bw_low = (req_bw > link_bw); - is_link_bw_min = ((cur_link_settings.link_rate <= LINK_RATE_LOW) && - (cur_link_settings.lane_count <= LANE_COUNT_ONE)); - - if (is_link_bw_low) - DC_LOG_WARNING("%s: Link bandwidth too low after fallback req_bw(%d) > link_bw(%d)\n", - __func__, req_bw, link_bw); + if (req_bw > link_bw) + break; } msleep(delay_between_attempts); @@ -3309,7 +3305,7 @@ static bool dp_verify_link_cap( int *fail_count) { struct dc_link_settings cur_link_settings = {0}; - struct dc_link_settings initial_link_settings = *known_limit_link_setting; + struct dc_link_settings max_link_settings = *known_limit_link_setting; bool success = false; bool skip_video_pattern; enum clock_source_id dp_cs_id = get_clock_source_id(link); @@ -3318,7 +3314,7 @@ static bool dp_verify_link_cap( struct link_resource link_res; memset(&irq_data, 0, sizeof(irq_data)); - cur_link_settings = initial_link_settings; + cur_link_settings = max_link_settings; /* Grant extended timeout request */ if ((link->lttpr_mode == LTTPR_MODE_NON_TRANSPARENT) && (link->dpcd_caps.lttpr_caps.max_ext_timeout > 0)) { @@ -3361,7 +3357,7 @@ static bool dp_verify_link_cap( dp_trace_lt_result_update(link, status, true); dp_disable_link_phy(link, &link_res, link->connector_signal); } while (!success && decide_fallback_link_setting(link, - initial_link_settings, &cur_link_settings, status)); + &max_link_settings, &cur_link_settings, status)); link->verified_link_cap = success ? cur_link_settings : fail_safe_link_settings; @@ -3596,16 +3592,19 @@ static bool decide_fallback_link_setting_max_bw_policy( */ static bool decide_fallback_link_setting( struct dc_link *link, - struct dc_link_settings initial_link_settings, - struct dc_link_settings *current_link_setting, + struct dc_link_settings *max, + struct dc_link_settings *cur, enum link_training_result training_result) { - if (!current_link_setting) + if (!cur) return false; - if (dp_get_link_encoding_format(&initial_link_settings) == DP_128b_132b_ENCODING || + if (!max) + return false; + + if (dp_get_link_encoding_format(max) == DP_128b_132b_ENCODING || link->dc->debug.force_dp2_lt_fallback_method) - return decide_fallback_link_setting_max_bw_policy(link, &initial_link_settings, - current_link_setting, training_result); + return decide_fallback_link_setting_max_bw_policy(link, max, cur, + training_result); switch (training_result) { case LINK_TRAINING_CR_FAIL_LANE0: @@ -3613,28 +3612,18 @@ static bool decide_fallback_link_setting( case LINK_TRAINING_CR_FAIL_LANE23: case LINK_TRAINING_LQA_FAIL: { - if (!reached_minimum_link_rate - (current_link_setting->link_rate)) { - current_link_setting->link_rate = - reduce_link_rate( - current_link_setting->link_rate); - } else if (!reached_minimum_lane_count - (current_link_setting->lane_count)) { - current_link_setting->link_rate = - initial_link_settings.link_rate; + if (!reached_minimum_link_rate(cur->link_rate)) { + cur->link_rate = reduce_link_rate(cur->link_rate); + } else if (!reached_minimum_lane_count(cur->lane_count)) { + cur->link_rate = max->link_rate; if (training_result == LINK_TRAINING_CR_FAIL_LANE0) return false; else if (training_result == LINK_TRAINING_CR_FAIL_LANE1) - current_link_setting->lane_count = - LANE_COUNT_ONE; - else if (training_result == - LINK_TRAINING_CR_FAIL_LANE23) - current_link_setting->lane_count = - LANE_COUNT_TWO; + cur->lane_count = LANE_COUNT_ONE; + else if (training_result == LINK_TRAINING_CR_FAIL_LANE23) + cur->lane_count = LANE_COUNT_TWO; else - current_link_setting->lane_count = - reduce_lane_count( - current_link_setting->lane_count); + cur->lane_count = reduce_lane_count(cur->lane_count); } else { return false; } @@ -3642,17 +3631,17 @@ static bool decide_fallback_link_setting( } case LINK_TRAINING_EQ_FAIL_EQ: { - if (!reached_minimum_lane_count - (current_link_setting->lane_count)) { - current_link_setting->lane_count = - reduce_lane_count( - current_link_setting->lane_count); - } else if (!reached_minimum_link_rate - (current_link_setting->link_rate)) { - current_link_setting->link_rate = - reduce_link_rate( - current_link_setting->link_rate); - current_link_setting->lane_count = initial_link_settings.lane_count; + if (!reached_minimum_lane_count(cur->lane_count)) { + cur->lane_count = reduce_lane_count(cur->lane_count); + } else if (!reached_minimum_link_rate(cur->link_rate)) { + cur->link_rate = reduce_link_rate(cur->link_rate); + /* Reduce max link rate to avoid potential infinite loop. + * Needed so that any subsequent CR_FAIL fallback can't + * re-set the link rate higher than the link rate from + * the latest EQ_FAIL fallback. + */ + max->link_rate = cur->link_rate; + cur->lane_count = max->lane_count; } else { return false; } @@ -3660,12 +3649,15 @@ static bool decide_fallback_link_setting( } case LINK_TRAINING_EQ_FAIL_CR: { - if (!reached_minimum_link_rate - (current_link_setting->link_rate)) { - current_link_setting->link_rate = - reduce_link_rate( - current_link_setting->link_rate); - current_link_setting->lane_count = initial_link_settings.lane_count; + if (!reached_minimum_link_rate(cur->link_rate)) { + cur->link_rate = reduce_link_rate(cur->link_rate); + /* Reduce max link rate to avoid potential infinite loop. + * Needed so that any subsequent CR_FAIL fallback can't + * re-set the link rate higher than the link rate from + * the latest EQ_FAIL fallback. + */ + max->link_rate = cur->link_rate; + cur->lane_count = max->lane_count; } else { return false; } -- 2.7.4