From a9bfe94cd7e3ab7d765bddc3a081268797fb427d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@linux.intel.com>
Date: Thu, 30 Sep 2021 16:43:07 +0300
Subject: drm/i915: Clear leftover DP vswing/preemphasis values before modeset
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Git-commit: 1e9ae61d172f92863c84e5745cc59d485f92bdea
Patch-mainline: v5.16-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225
Currently we clear the leftover vswing/preemphasis values only
at the start of link training. That means the initial vswing
programming performed during modeset is going to use stale values
left over from the previous link training sequence, and then at
the start of link training we're going to reset the levels back
to 0. Seems much better to make sure we start with level 0 from
the get go.
Additionally if LTTPRs are present the leftover vswing/preemphasis
values are those of the last link in the chain, so not the values
that our PHY is even using after a successful link training sequence.
So let's make sure everything is cleared up before we start
programming anything.
Suggested-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210930134310.31669-1-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/i915/display/intel_dp.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index f0554c8110ad..2d0ca857b92a 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -1835,6 +1835,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
void intel_dp_set_link_params(struct intel_dp *intel_dp,
int link_rate, int lane_count)
{
+ memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
intel_dp->link_trained = false;
intel_dp->link_rate = link_rate;
intel_dp->lane_count = lane_count;
--
2.38.1