[PATCH 16/87] drm/amd/display: skip retrain in dc_link_set_preferred_link_settings() if using passive dongle

[sunpeng.li at amd.com]

From: Samson Tam <Samson.Tam at amd.com>

[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 at amd.com>
Reviewed-by: Jun Lei <Jun.Lei at amd.com>
Acked-by: Leo Li <sunpeng.li at amd.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

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 0918c334f0e2..02a18f6aa009 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -2998,8 +2998,10 @@ 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++) {
-- 
2.22.0