100% reproducible issue found on SKL SkullCanyon NUC with two external DP daisy-chained monitors in DP/MST mode. When turning off or changing the input of the second monitor the machine stops with a kernel oops. This issue happened with 4.8.8 as well as drm/drm-intel-nightly. This issue is traced to an inconsistent control flow in drm_dp_update_payload_part1(): the 'port' pointer is set to NULL at the same time as'req_payload.num_slots' is set to zero, but the pointer is dereferenced even when req_payload.num_slot is zero. Fix by adding test condition to make sure both variables are used consistently. This removes the kernel oops. There are still annoying cases where the primary display goes black when the secondary display is turned off but it can be recovered from by playing with the monitor inputs and power buttons. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98990 Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx> --- drivers/gpu/drm/drm_dp_mst_topology.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index aa64448..5481fde 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -1815,7 +1815,7 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr) drm_dp_create_payload_step1(mgr, mgr->proposed_vcpis[i]->vcpi, &req_payload); mgr->payloads[i].num_slots = req_payload.num_slots; mgr->payloads[i].vcpi = req_payload.vcpi; - } else if (mgr->payloads[i].num_slots) { + } else if (mgr->payloads[i].num_slots && port != NULL) { mgr->payloads[i].num_slots = 0; drm_dp_destroy_payload_step1(mgr, port, port->vcpi.vcpi, &mgr->payloads[i]); req_payload.payload_state = mgr->payloads[i].payload_state; -- 2.7.4 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
