From 4de737a26e6a251c86ff1e96667aebc5eecf9456 Mon Sep 17 00:00:00 2001 From: Nathan Ciobanu Date: Tue, 24 Jul 2018 15:33:32 -0700 Subject: [PATCH] drm/i915/dp: Improve clock recovery loop limit comment Clarifies the clock recovery loop limit comment that 80 max_cr_tries for pre-DP1.4 devices was chosen as a very tolerant upper bound. Assumptions made: - DP1.4 syncs should be smarter so they won't need more than 10 tries - pre-DP1.4 syncs should be compliant enough to not need that many tries (80) but we should tolerate any that may trigger this corner case Cc: Dhinakaran Pandiyan Cc: Rodrigo Vivi Cc: Marc Herbert Suggested-by: Marc Herbert Signed-off-by: Nathan Ciobanu Reviewed-by: Marc Herbert Signed-off-by: Rodrigo Vivi Link: https://patchwork.freedesktop.org/patch/msgid/1532471612-30001-1-git-send-email-nathan.d.ciobanu@linux.intel.com --- drivers/gpu/drm/i915/intel_dp_link_training.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c index 07e128c7443c..a9f40985a621 100644 --- a/drivers/gpu/drm/i915/intel_dp_link_training.c +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c @@ -172,10 +172,12 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp) } /* - * 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) + * The DP 1.4 spec defines the max clock recovery retries value + * as 10 but for pre-DP 1.4 devices we set a very tolerant + * retry limit of 80 (4 voltage levels x 4 preemphasis levels x + * x 5 identical voltage retries). Since the previous specs didn't + * define a limit and created the possibility of an infinite loop + * we want to prevent any sync from triggering that corner case. */ if (intel_dp->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14) max_cr_tries = 10; -- 2.30.2