drm/amd/display: skip retrain in dc_link_set_preferred_link_settings() if using passi...

[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>

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
index 8dbf759eba45339e37b0265c334bf9fe7c0d6525..435d50356bad5a1674157231895c45120a7abedd 100644 (file)
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -2984,8 +2984,10 @@ void dc_link_set_preferred_link_settings(struct dc *dc,
 
        /* Retrain with preferred link settings only relevant for
         * 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;
 
        for (i = 0; i < MAX_PIPES; i++) {