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Subject[PATCH AUTOSEL 5.4 09/52] drm/amd/display: Change the delay time before enabling FEC
Date
From: "Leo (Hanghong) Ma" <hanghong.ma@amd.com>

[ Upstream commit 28fa24ad14e8f7d23c62283eaf9c79b4fd165c16 ]

[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>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 f5742719b5d9b..b6e68e9c81d11 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
@@ -3490,7 +3490,14 @@ 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) {
--
2.20.1
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