From dd00b8b9cac3276819178db8334a71df63b583ba Mon Sep 17 00:00:00 2001 From: Dale Zhao Date: Wed, 21 Oct 2020 21:09:16 +0800 Subject: [PATCH] drm/amd/display: WA to ensure MUX chip gets SUPPORTED_LINK_RATES of eDP [Why] Customer make a request to add this WA by driver. Some MUX chips will power down with eDP 1.4 panel and lose previous supported link rates(DPCD 0x010) in customer's hybrid-GPU designs. As a result, during sleep resuming and screen turns on from idle, link training will be performed incorrectly and eDP will flicker or black screen. These MUX chips need source to read DPCD 0x010 again during LKT so that it can restore supported link rates of panel. For driver side, supported link rate set is fetched when link detection, no need to update but just read again as WA. [How] Read DPCD 0x010 again during link training for eDP 1.4. Signed-off-by: Dale Zhao Reviewed-by: Wenjing Liu Acked-by: Qingqing Zhuo Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 10 ++++++++++ 1 file changed, 10 insertions(+) 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 d30ef6ea19472..8a7c4de49a4b4 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 @@ -183,6 +183,16 @@ static void dpcd_set_link_settings( if (link->dpcd_caps.dpcd_rev.raw >= DPCD_REV_14 && lt_settings->link_settings.use_link_rate_set == true) { rate = 0; + /* WA for some MUX chips that will power down with eDP and lose supported + * link rate set for eDP 1.4. Source reads DPCD 0x010 again to ensure + * MUX chip gets link rate set back before link training. + */ + if (link->connector_signal == SIGNAL_TYPE_EDP) { + uint8_t supported_link_rates[16]; + + core_link_read_dpcd(link, DP_SUPPORTED_LINK_RATES, + supported_link_rates, sizeof(supported_link_rates)); + } core_link_write_dpcd(link, DP_LINK_BW_SET, &rate, 1); core_link_write_dpcd(link, DP_LINK_RATE_SET, <_settings->link_settings.link_rate_set, 1); -- 2.39.5