[0/2] Take SST-only branch device into account

Message

Lin, Wayne Jan. 8, 2020, 8:44 a.m. UTC

Noticed this while testing 4 ports MST hub from StarTech.com.
While plugging in and display a MST monitor(Dell U2417H), change the MST
feature to off from OSD. Monitor then can't display anymore.

After analyzing, found out that the CSN reports the specific port from
Device with MST Branching Unit (Message_Capability_Status=1 &&
Peer_Device_Type=010) to SST-only Branch Device ((Message_Capability_Status=0 &&
Peer_Device_Type=010). Current code expects peer device as MST branch
device and can handle sideband message once the peer device type is
declared as Peer_Device_Type=010. But for SST-only Branch Device, its
Peer_Device_Type is 010 and can't handle sideband message. For this case,
we should follow the same handling procedure as the case in
DP_PEER_DEVICE_DP_LEGACY_CONV & DP_PEER_DEVICE_SST_SINK.

This series is trying to add the SST-only branch device case in and remain
the original processing logic in current code.

Wayne Lin (2):
  drm/dp_mst: Add a function to determine the mst end device
  drm/dp_mst: Handle SST-only branch device case

 drivers/gpu/drm/drm_dp_mst_topology.c | 147 +++++++++++++++-----------
 1 file changed, 84 insertions(+), 63 deletions(-)