This is a note to let you know that I've just added the patch titled drm/amd/display: Change the delay time before enabling FEC to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-amd-display-change-the-delay-time-before-enablin.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 6e83ba3ad217cf16d6d10315a67915fcbc9751d1 Author: Leo (Hanghong) Ma <hanghong.ma@xxxxxxx> Date: Thu Nov 7 16:30:04 2019 -0500 drm/amd/display: Change the delay time before enabling FEC [ 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@xxxxxxx> Reviewed-by: Harry Wentland <Harry.Wentland@xxxxxxx> Reviewed-by: Nikola Cornij <Nikola.Cornij@xxxxxxx> Acked-by: Leo Li <sunpeng.li@xxxxxxx> Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> 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) {