linux-kernel - [PATCH 5.4 009/191] drm/amd/display: Change the delay time before enabling FEC

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Date:   Tue,  7 Jan 2020 21:52:09 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Leo (Hanghong) Ma" <hanghong.ma@....com>,
        Harry Wentland <Harry.Wentland@....com>,
        Nikola Cornij <Nikola.Cornij@....com>,
        Leo Li <sunpeng.li@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 009/191] drm/amd/display: Change the delay time before enabling FEC

From: Leo (Hanghong) Ma <hanghong.ma@....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@....com>
Reviewed-by: Harry Wentland <Harry.Wentland@....com>
Reviewed-by: Nikola Cornij <Nikola.Cornij@....com>
Acked-by: Leo Li <sunpeng.li@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.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 5a583707d198..0ab890c927ec 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
@@ -3492,7 +3492,14 @@ 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