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From 9dfa55f00ad9fc538d374cfc59d35b63b51f653a Mon Sep 17 00:00:00 2001
From: "Leo (Hanghong) Ma" <hanghong.ma@amd.com>
Date: Thu, 7 Nov 2019 16:30:04 -0500
Subject: [PATCH 4684/4736] drm/amd/display: Change the delay time before
enabling FEC
[why]
DP spec requires 1000 symbols delay between the end of link training
and enabling FEC in the stream. Currently we are using 1 miliseconds
delay which is not accurate.
[how]
One lane RBR should have the maximum time for transmitting 1000 LL
codes which is 6.173 us. So using 7 microseconds delay instead of
1 miliseconds.
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Reviewed-by: Nikola Cornij <Nikola.Cornij@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
---
drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
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 537b4dee8f22..b10019106030 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
@@ -3951,7 +3951,14 @@ void dp_set_fec_enable(struct dc_link *link, bool enable)
if (link_enc->funcs->fec_set_enable &&
link->dpcd_caps.fec_cap.bits.FEC_CAPABLE) {
if (link->fec_state == dc_link_fec_ready && enable) {
- msleep(1);
+ /* Accord to DP spec, FEC enable sequence can first
+ * be transmitted anytime after 1000 LL codes have
+ * been transmitted on the link after link training
+ * completion. Using 1 lane RBR should have the maximum
+ * time for transmitting 1000 LL codes which is 6.173 us.
+ * So use 7 microseconds delay instead.
+ */
+ udelay(7);
link_enc->funcs->fec_set_enable(link_enc, true);
link->fec_state = dc_link_fec_enabled;
} else if (link->fec_state == dc_link_fec_enabled && !enable) {
--
2.17.1
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