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drm/amd/display: skip retrain in dc_link_set_preferred_link_settings() if using passive dongle 

[Why]
Fixes issue when we have a display connected using a passive
dongle and then emulate over it using a DP connection at 1 x 1.62 Ghz.
System hangs because register bus returns back 0xFFFFFFFF for all
register reads after setting register DIG_BE_CNTL in
dcn10_link_encoder_connect_dig_be_to_fe().  Hang occurs later
when trying to do a register read.

[How]
At the start of the emulation, dc_link_set_preferred_link_settings()
and dp_retrain_link_dp_test() is called, even though it is connected
using a passive dongle.

Add an extra condition in dp_retrain_link_dp_test() to check for
link->dongle_max_pix_clk > 0.  This is the only way we know if the
connection is using passive dongle so we don't retrain DP.

Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Samson Tam 2019-06-04 15:52:59 -04:00 committed by Alex Deucher
parent 4a876eecf6
commit 4fc1609bcd
1 changed files with 3 additions and 1 deletions
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4
drivers/gpu/drm/amd/display/dc/core/dc_link.c
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@ -2984,8 +2984,10 @@ void dc_link_set_preferred_link_settings(struct dc *dc,
/* Retrain with preferred link settings only relevant for /* Retrain with preferred link settings only relevant for
* DP signal type * DP signal type
* Check for non-DP signal or if passive dongle present
*/ */
if (!dc_is_dp_signal(link->connector_signal)) if (!dc_is_dp_signal(link->connector_signal) ||
link->dongle_max_pix_clk > 0)
return; return;
for (i = 0; i < MAX_PIPES; i++) { for (i = 0; i < MAX_PIPES; i++) {