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drm/i915/dp_mst: Fix configuring FEC for a disconnected stream

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During an atomic commit after all the MST stream CRTC state is computed
the driver ensures that the FEC is configured the same way (enabled or
disabled) for all the streams on a given MST topology's link.
drm_dp_mst_port_downstream_of_parent() used to determine if a stream is
downstream of an MST port will return false if the whole topology is
disconnected, since in that case it can't verify that the port/
parent_port passed to it is in the given MST topology. This is a problem
during the above FEC configuration check, since
intel_dp_mst_check_dsc_change()->get_pipes_downstream_of_mst_ports()
will not return all the stream CRTCs/pipes for the topology as expected.
Since passing parent_port==NULL to get_pipes_downstream_of_mst_port()
is meant to return all the streams for the given topology (i.e. mst_mgr)
skip checking if an MST port is downstream of a parent port in this
case.

This fixes a problem where the FEC configuration check explained above
failed to ensure that all streams' FEC is configured the same way if the
topology was disconnected, leading to a FEC state mismatch error.

Cc: stable@vger.kernel.org # v6.10+
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16073
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16384
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260907174413.741851-1-imre.deak@intel.com
(cherry picked from commit 270681fbffbba2b6ccf5b7e3c34b8b563b36167f)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
This commit is contained in:
Imre Deak 2026-09-07 20:44:12 +03:00 committed by Jani Nikula
parent 5271d81f99
commit acbe9a3b60
1 changed files with 2 additions and 1 deletions
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3
drivers/gpu/drm/i915/display/intel_dp_mst.c
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@ -852,7 +852,8 @@ static u8 get_pipes_downstream_of_mst_port(struct intel_atomic_state *state,
if (&connector->mst.dp->mst.mgr != mst_mgr)
continue;
if (connector->mst.port != parent_port &&
if (parent_port &&
connector->mst.port != parent_port &&
!drm_dp_mst_port_downstream_of_parent(mst_mgr,
connector->mst.port,
parent_port))