[PATCH 4/7] drm/i915: Work around spurious long HPD pulses breaking MST detectiong

[Imre Deak]

When switching to MST mode some displays send long HPD pulses. During
the disconnected state MST sideband messaging will fail, and normally we
would have to restart the MST probing (with the assumption that the
monitor will not send a long HPD pulse during the second attempt).

The above reprobing could be done in response to an HPD interrupt,
however the IOM seems to suppress these interrupts at time. To work
around this, wait for any long HPD pulses to pass, before starting the
MST probing.

Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 42589cae766d..14851053f313 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4732,6 +4732,8 @@ intel_dp_configure_mst(struct intel_dp *intel_dp)
 	intel_dp->is_mst = sink_can_mst &&
 		i915_modparams.enable_dp_mst;
 
+	msleep(1500);
+
 	drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr,
 					intel_dp->is_mst);
 }
-- 
2.23.1