From owner-freebsd-acpi@freebsd.org  Sat Oct 17 15:09:11 2015
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From: Eric McCorkle <eric@metricspace.net>
Subject: Old suspend/resume issue likely root cause
Message-ID: <5622648F.2090509@metricspace.net>
Date: Sat, 17 Oct 2015 11:09:03 -0400
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A while back (in May or June or so), I was attempting to figure out why 
my laptop screen stayed blank on suspend/resume.  I posted some dmesg 
outputs and theorized that it might be something about the devices 
coming back up in the wrong order.  John Baldwin suggested I try doing 
hw.pci.do_power_suspend=0.

I got tangled up with other projects and had to set it aside.  However, 
I now finally have more information:


* hw.pci.power_suspend=0 does cause the screen to come back up properly. 
  The network (wireless via iwm driver) needs to be re-initialized, but 
everything else seems to work properly.

* Without hw.pci.power_suspend=0, the issue persists even when booting 
from EFI, so we can rule out some kind of legacy BIOS issue.  The issue 
manifests even with the experimental i915 driver, so we can rule out 
something with the efifb or VGA framebuffer drivers.


Based on this, it looks pretty likely that the pci bus is the culprit. 
Any suggestions on where to look?