[PATCH 1/2] drm/amd/display: Retrain dongles when SINK_COUNT becomes non-zero

[Harry Wentland]

[WHY]
Two years ago the patch referenced by the Fixes tag stopped running
dp_verify_link_cap_with_retries during DP detection when the reason
for the detection was a short-pulse interrupt. This effectively meant
that we were no longer doing the verify_link_cap training on active
dongles when their SINK_COUNT changed from 0 to 1.

A year ago this was partly remedied with this commit:
80adaebd2d41 drm/amd/display: Don't skip link training for empty dongle

This made sure that we trained the dongle on initial hotplug (without
connected downstream devices).

This is all fine and dandy if it weren't for the fact that there are
some dongles on the market that don't like link training when SINK_COUNT
is 0 These dongles will in fact indicate a SINK_COUNT of 0 immediately
after hotplug, even when a downstream device is connected, and then
trigger a shortpulse interrupt indicating a SINK_COUNT change to 1.

In order to play nicely we will need our policy to not link train an
active DP dongle when SINK_COUNT is 0 but ensure we train it when the
SINK_COUNT changes to 1.

[HOW]
Call dp_verify_link_cap_with_retries on detection even when the detection
is triggered from a short pulse interrupt.

With this change we can also revert this commit which we'll do in a separate
follow-up change:
80adaebd2d41 drm/amd/display: Don't skip link training for empty dongle

Fixes: 0301ccbaf67d drm/amd/display: DP Compliance 400.1.1 failure
Suggested-by: Louis Li <Ching-shih.Li at amd.com>
Tested-by: Louis Li <Ching-shih.Li at amd.com>
Cc: Wenjing Liu <Wenjing.Liu at amd.com>
Cc: Hersen Wu <hersenxs.wu at amd.com>
Cc: Eric Yang <Eric.Yang2 at amd.com>
Signed-off-by: Harry Wentland <harry.wentland at amd.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

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 a50768a7ba68..cc2e05003595 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -969,8 +969,7 @@ static bool dc_link_detect_helper(struct dc_link *link,
 			same_edid = is_same_edid(&prev_sink->dc_edid, &sink->dc_edid);
 
 		if (link->connector_signal == SIGNAL_TYPE_DISPLAY_PORT &&
-			sink_caps.transaction_type == DDC_TRANSACTION_TYPE_I2C_OVER_AUX &&
-			reason != DETECT_REASON_HPDRX) {
+			sink_caps.transaction_type == DDC_TRANSACTION_TYPE_I2C_OVER_AUX) {
 			/*
 			 * TODO debug why Dell 2413 doesn't like
 			 *  two link trainings
-- 
2.25.0