From 8633d96d3ca14b37dffe303281c1dff320b422fb Mon Sep 17 00:00:00 2001 From: Anthony Koo Date: Wed, 15 May 2019 16:39:23 -0400 Subject: [PATCH] drm/amd/display: fix issues with bad AUX reply on some displays [Why] Some displays take some time to power up AUX CH once they are put into D3 state via write to DPCD 600h=2. Interestingly enough, some display may simply NACK, but some might also ACK with a bunch of 0s, which can cause issues with receiver cap retrieval. Note that not all DPCD address return 0s, but in particular it has been observed on some higher DPCD address such as DPCD 2200h, etc. [How] Based on spec, receiver will monitor differential signal while in D3 and AUX CH is in low power mode. When detected, it may allow up to 1 ms to power up AUX CH and reply. If we read Sink power state D3, we should add 1 ms delay to satisfy this spec requirement. Signed-off-by: Anthony Koo Reviewed-by: Wenjing Liu Acked-by: Leo Li Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 12 ++++++++++++ 1 file changed, 12 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 1ee544a32ebb..65d6caedbd82 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 @@ -2361,6 +2361,7 @@ static bool retrieve_link_cap(struct dc_link *link) /*Only need to read 1 byte starting from DP_DPRX_FEATURE_ENUMERATION_LIST. */ uint8_t dpcd_dprx_data = '\0'; + uint8_t dpcd_power_state = '\0'; struct dp_device_vendor_id sink_id; union down_stream_port_count down_strm_port_count; @@ -2377,6 +2378,17 @@ static bool retrieve_link_cap(struct dc_link *link) memset(&edp_config_cap, '\0', sizeof(union edp_configuration_cap)); + status = core_link_read_dpcd(link, DP_SET_POWER, + &dpcd_power_state, sizeof(dpcd_power_state)); + + /* Delay 1 ms if AUX CH is in power down state. Based on spec + * section 2.3.1.2, if AUX CH may be powered down due to + * write to DPCD 600h = 2. Sink AUX CH is monitoring differential + * signal and may need up to 1 ms before being able to reply. + */ + if (status != DC_OK || dpcd_power_state == DP_SET_POWER_D3) + udelay(1000); + for (i = 0; i < read_dpcd_retry_cnt; i++) { status = core_link_read_dpcd( link, -- 2.30.2