[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 <anthony.koo@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
8633d96d3c