Dell monitor with a built-in MST branch does not light up on boot when
connected to a Thinkpad dock. The monitor also does not wake up after
Suspend-to-Idle or dpms off in this configuration. Keeping the AUX
powered up in the D3 power state solved this problem.

This partially fixes
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90963

Cc: Ethan Hsieh <ethan.hs...@canonical.com>
Cc: Lyude <cp...@redhat.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandi...@intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 76c8a0b..5595367 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2485,7 +2485,11 @@ void intel_dp_sink_dpms(struct intel_dp *intel_dp, int 
mode)
                return;
 
        if (mode != DRM_MODE_DPMS_ON) {
-               ret = drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
+               if (intel_dp->is_mst)
+                       ret = drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
+                                        DP_SET_POWER_D3_AUX_ON);
+               else
+                       ret = drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
                                         DP_SET_POWER_D3);
        } else {
                struct intel_lspcon *lspcon = dp_to_lspcon(intel_dp);
-- 
2.7.4

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