From: Nathan Ciobanu <nathan.d.ciobanu@linux.intel.com>
To: intel-gfx@lists.freedesktop.org
Cc: Marc Herbert <marc.herbert@intel.com>,
Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>,
Rodrigo Vivi <rodrigo.vivi@intel.com>
Subject: [PATCH] drm/i915/dp: Improve clock recovery loop limit comment
Date: Tue, 24 Jul 2018 15:33:32 -0700 [thread overview]
Message-ID: <1532471612-30001-1-git-send-email-nathan.d.ciobanu@linux.intel.com> (raw)
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 <dhinakaran.pandiyan@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Marc Herbert <marc.herbert@intel.com>
Suggested-by: Marc Herbert <marc.herbert@intel.com>
Signed-off-by: Nathan Ciobanu <nathan.d.ciobanu@linux.intel.com>
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 @@ static bool intel_dp_link_max_vswing_reached(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;
--
1.9.1
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next reply other threads:[~2018-07-24 22:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-24 22:33 Nathan Ciobanu [this message]
2018-07-24 23:17 ` ✓ Fi.CI.BAT: success for drm/i915/dp: Improve clock recovery loop limit comment Patchwork
2018-07-25 0:17 ` [PATCH] " Marc Herbert
2018-07-25 17:00 ` Rodrigo Vivi
2018-07-25 0:45 ` ✗ Fi.CI.IGT: failure for " Patchwork
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