From bb5ffe6fd58cd37f1cade411c4a00745ed0fbbd1 Mon Sep 17 00:00:00 2001 From: Nathan Ciobanu Date: Fri, 20 Jul 2018 14:44:12 -0700 Subject: [PATCH] drm/i915/dp: Limit link training clock recovery loop Limit the link training clock recovery loop to 10 attempts at LANEx_CR_DONE per DP 1.4 spec section 3.5.1.2.2 and 80 attempts for pre-DP 1.4 (4 voltage levels x 4 preemphasis levels x x 5 identical voltages tries). Some faulty USB-C MST hubs can cause us to get stuck in this loop indefinitely requesting something like: voltage swing: 0, pre-emphasis level: 2 voltage swing: 1, pre-emphasis level: 2 voltage swing: 0, pre-emphasis level: 3 over and over so max_vswing would never be reached, drm_dp_clock_recovery_ok() would never return true and voltage_tries would always get reset to 1. The driver sends those values to the hub but the hub keeps requesting new values every time. Changes in v2: - updated commit message (DK, Manasi) - defined DP_DP14_MAX_CR_TRIES (Marc) - made the loop iterate for max 10 times (Rodrigo, Marc) Changes in v3: - changed error message to use DP_DP14_MAX_CR_TRIES Changes in v4: - Updated the title to reflect the change - Updated the commit message - Added 80 attempts for pre-DP 1.4 devices Changes in v5: - Removed DP_DP14_MAX_CR_TRIES from drm v6: Updated comment to match kernel style (Rodrigo) Cc: Dhinakaran Pandiyan Cc: Rodrigo Vivi Cc: Marc Herbert Cc: Manasi Navare Signed-off-by: Nathan Ciobanu Reviewed-by: Rodrigo Vivi Signed-off-by: Rodrigo Vivi Link: https://patchwork.freedesktop.org/patch/msgid/20180720214413.29506-1-rodrigo.vivi@intel.com --- drivers/gpu/drm/i915/intel_dp_link_training.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c index 4da6e33c7fa1..299cad5632ed 100644 --- a/drivers/gpu/drm/i915/intel_dp_link_training.c +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c @@ -129,7 +129,7 @@ static bool intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp) { uint8_t voltage; - int voltage_tries, max_vswing_tries; + int voltage_tries, max_vswing_tries, cr_tries, max_cr_tries; uint8_t link_config[2]; uint8_t link_bw, rate_select; @@ -170,9 +170,20 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp) return false; } + /* + * DP 1.4 spec clock recovery retries defined but + * for devices pre-DP 1.4 we set the retry limit + * to 4 (voltage levels) x 4 (preemphasis levels) x + * x 5 (same voltage retries) = 80 (max iterations) + */ + if (intel_dp->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14) + max_cr_tries = 10; + else + max_cr_tries = 80; + voltage_tries = 1; max_vswing_tries = 0; - for (;;) { + for (cr_tries = 0; cr_tries < max_cr_tries; ++cr_tries) { uint8_t link_status[DP_LINK_STATUS_SIZE]; drm_dp_link_train_clock_recovery_delay(intel_dp->dpcd); @@ -216,6 +227,8 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp) ++max_vswing_tries; } + DRM_ERROR("Failed clock recovery %d times, giving up!\n", max_cr_tries); + return false; } /* -- 2.30.2