drm/i915/dp: Disable UHBR link configs with 1/2 lanes

Disable 1 and 2 lane link configurations on UHBR tunneled links,
according to DP Standard v2.1b "3.5.2.16.3 128b/132b DPRX Lane Count
Conversion Failure Indication and Corrective Action". A tunnel can
indicate if it's not affected by this limitation, check for that and
skip disabling the unsupported lanes for a well-behaving tunnel.

The Standard in the same section also describes a workaround for 2 lanes
which requires assisstance from the sink, where the sink indicates at
the end of the link training sequence if the link training must be
retried. This mechanism also requires quirking out some sinks - based on
the sink's DPCD OUI and EDID identifications - which doesn't implement
this link training feedback indication properly. This patch leaves the
implementation of this workaround for a follow-up, but prepares for it
already by detecting the supported number of lane counts at a place
where both DPCD OUI and EDID is available for the quirk detection.

Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260714152700.555527-6-imre.deak@intel.com

0 files changed, 0 insertions, 0 deletions