It's possible to modeset a connector/mst port that has a 0 full_pbn value: if the sink on the port deasserts its HPD and a branch device reports this via a CSN with the port's ddps=0 and pdt!=NONE the driver clears full_pbn, but the corresponding connector can be still modesetted.
This happened on a DELL U2719D monitor as the branch device and an LG 27UL650-W daisy-chained to it, the LG monitor generating a long HPD pulse (doing this for some reason always when waking up from some power saving state).
Tune down the WARN about this scenario to a debug message.
References: https://gitlab.freedesktop.org/drm/intel/-/issues/1917 Cc: Lyude Paul lyude@redhat.com Signed-off-by: Imre Deak imre.deak@intel.com --- drivers/gpu/drm/drm_dp_mst_topology.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 0a54506c27738..dcaf4bf9b62f6 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -5118,11 +5118,15 @@ drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port, if (!found) return 0;
- /* This should never happen, as it means we tried to - * set a mode before querying the full_pbn + /* + * This could happen if the sink deasserted its HPD line, but + * the branch device still reports it as attached (PDT != NONE). */ - if (WARN_ON(!port->full_pbn)) + if (!port->full_pbn) { + drm_dbg_kms(port->mgr->dev, "[MSTB:%p] [MST PORT:%p] no BW available for the port\n", + port->parent, port); return -EINVAL; + }
pbn_used = vcpi->pbn; } else {