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Subject[PATCH 4.19 15/41] drm/amd/dm: Dont forget to attach MST encoders
4.19-stable review patch.  If anyone has any objections, please let me know.


From: Lyude Paul <>

commit c9e0ab86b2e03154bb898cd2f851827783224727 upstream.

The change fixed huge delay in SST daisy chain and S3 soft hang
observed in 4.19 kernel rebase.

Regression point in drm:
drm/fb-helper: Eliminate the .best_encoder() usage

The aux sequence is altered due to the failure in
drm_connector_for_each_possible_encoder(). The failure is
caused by missing attached encoder in the process of adding
MST connector.
drm_dp_send_enum_path_resources() aux transaction is pushed after
mode probe, which causes conflict to drm_dp_mst_i2c_xfer(),
leading to the transaction timeout.

Signed-off-by: Lyude Paul <>
Reviewed-by: Jerry (Fangzhi) Zuo <>
Cc: Stable <>
Signed-off-by: Alex Deucher <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 2 ++
1 file changed, 2 insertions(+)

--- 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
@@ -374,6 +374,8 @@ dm_dp_add_mst_connector(struct drm_dp_ms

aconnector->mst_encoder = dm_dp_create_fake_mst_encoder(master);
+ drm_connector_attach_encoder(&aconnector->base,
+ &aconnector->mst_encoder->base);

* TODO: understand why this one is needed

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