From: Dale Zhao <[email protected]> [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 <[email protected]> Reviewed-by: Wenjing Liu <[email protected]> Acked-by: Qingqing Zhuo <[email protected]> --- 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 9d1c5e1d06c0..54ac3de4e8e0 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); -- 2.17.1 _______________________________________________ amd-gfx mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/amd-gfx
