[PATCH 13/15] drm/amd/display: TMDS Fallback transition

[Qingqing Zhuo]

From: Chris Park <Chris.Park at amd.com>

[Why]
HDMI requires fallback to TMDS by redetection
in order to switch PHY settings.
This avoids black out when link training fail
during mode setting, link quality update,
disable driver sequence.

[How]
Allow driver to redetect HDMI displays
based on retraining or fallback mechanism.

Signed-off-by: Chris Park <Chris.Park at amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr at amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo at amd.com>
---
 .../drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 13 +++++++++++++
 drivers/gpu/drm/amd/display/dc/dc_link.h            |  2 ++
 2 files changed, 15 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index 0b9a4fc642ae..98b4d5e2e336 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -158,7 +158,20 @@ static bool validate_dsc_caps_on_connector(struct amdgpu_dm_connector *aconnecto
 	u8 dsc_caps[16] = { 0 };
 
 	aconnector->dsc_aux = drm_dp_mst_dsc_aux_for_port(port);
+#if defined(CONFIG_HP_HOOK_WORKAROUND)
+	/*
+	 * drm_dp_mst_dsc_aux_for_port() will return NULL for certain configs
+	 * because it only check the dsc/fec caps of the "port variable" and not the dock
+	 *
+	 * This case will return NULL: DSC capabe MST dock connected to a non fec/dsc capable display
+	 *
+	 * Workaround: explicitly check the use case above and use the mst dock's aux as dsc_aux
+	 *
+	 */
 
+	if (!aconnector->dsc_aux && !port->parent->port_parent)
+		aconnector->dsc_aux = &aconnector->mst_port->dm_dp_aux.aux;
+#endif
 	if (!aconnector->dsc_aux)
 		return false;
 
diff --git a/drivers/gpu/drm/amd/display/dc/dc_link.h b/drivers/gpu/drm/amd/display/dc/dc_link.h
index e002ef706e1d..266b93a705d5 100644
--- a/drivers/gpu/drm/amd/display/dc/dc_link.h
+++ b/drivers/gpu/drm/amd/display/dc/dc_link.h
@@ -237,6 +237,8 @@ enum dc_detect_reason {
 	DETECT_REASON_BOOT,
 	DETECT_REASON_HPD,
 	DETECT_REASON_HPDRX,
+	DETECT_REASON_FALLBACK,
+	DETECT_REASON_RETRAIN
 };
 
 bool dc_link_detect(struct dc_link *dc_link, enum dc_detect_reason reason);
-- 
2.17.1