Well, I do know what is the root cause of this issue.
PSR does not get reset when frecon sets video mode and external monitor is connected.
With single monitor PSR is disabled when fecpn does video mdoe st,

Well, it looks like this is the CL that broke it https://chromium-review.googlesource.com/241434

Setting psr.setup_done to false, prevents any future call to intel_edp_psr_update from doing anything useful. So when we switch video mode in frecon it psr status is not updated even though it should be.

This only happens with two monitors, because haswell_crtc_enable for 2nd monitor breaks psr.setup_done

I think if we need to force full psr setup on every enable, we shoult set psr.setup_done inside EDP section of intel_disable_ddi. This would guarantee it is called only once, when ddi is being disabled, not per crtc.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/kernel/+/017ef43878b593b64296fbe091cf949d106473e5

commit 017ef43878b593b64296fbe091cf949d106473e5
Author: Dominik Behr <dbehr@chromium.org>
Date: Thu Sep 15 22:47:22 2016

CHROMIUM: drm/i915: reset psr.setup_done in disable_ddi instead of crtc_enable

haswell_crtc_enable() is not a good place to reset psr.setup_done because
connecting 2nd monitor will trigger haswell_crtc_enable() for another crtc and
prevent intel_edp_psr_update() from working at all. PSR state is really associated
with EDP link, not with CRTC.

BUG= chromium:628385 
TEST=switch to VT2 with external monitor connected

Change-Id: Iabddd2d936d48e969a2ab7ec500187ac3e1a6072
Signed-off-by: Dominik Behr <dbehr@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/386158
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>

[modify] https://crrev.com/017ef43878b593b64296fbe091cf949d106473e5/drivers/gpu/drm/i915/intel_display.c
[modify] https://crrev.com/017ef43878b593b64296fbe091cf949d106473e5/drivers/gpu/drm/i915/intel_ddi.c