[Intel-gfx] periodic wakeup from DPMS suspend

[Johannes Stezenbach]

On Wed, Oct 07, 2015 at 01:26:32PM +0200, Johannes Stezenbach wrote:
> On Tue, Oct 06, 2015 at 11:04:53PM -0400, Alex Deucher wrote:
> > On Tue, Oct 6, 2015 at 11:10 AM, Johannes Stezenbach <js at sig21.net> wrote:
> > >
> > > I have a NEC EA244WMi monitor connected to an Asus P8H77-V
> > > mainboard with Ivy Bridge Core i5-3550 via DVI.
> > > If DPMS suspend is enabled (by xscreensaver, or for testing by
> > > "xset dpms force off/suspend/standby"), the monitor
> > > enters standby mode but wakes up every 10...30 seconds for
> > > 6 seconds to display a "DVI-D: no signal" message.
> > 
> > Some monitors periodically scan all of their inputs if they are not
> > actively being driven by anything to try and automatically switch to
> > the connected input.  When the monitor scans the DVI input, it sees
> > load on the pins and turns on, only to realize it's not getting a
> > signal and then turns off.  If your monitor has an option to turn off
> > input probing, that might help.
> 
> It's not like I didn't try to twiddle just about every
> available menu item, and also used the monitor's
> "Reset to Factory Defaults" to no avail.
> However, while trying again I found a hidden menu item
> which is only available during the short time the
> "No Signal" message is displayed, where the left/right
> touch buttons open a "Scan Time" setting with "Normal"
> and "Slow" options.  After I changed it, the issue was
> solved.  I changed it back and the issue doesn't reproduce.
> So it looks some internal configuration of the monitor
> was messed up and is now fixed by twiddling the hidden
> menu item.  "Scan Time" is not documented in the manual
> nor is there an indication in the "No Signal" popup.
> 
> Case closed.

And I just came back to see the monitor doing the
wakeup cycling again.  To try something differerent
I unplugged the charger of the laptop sitting nearby
in suspend.  Bingo!  So it looks like an EMI issue.
I tried a few times and could reproduce twice and
then no more :-(  Now the monitor wakes up once
every 5min or so...

Which brings me back to a previous question:

> maybe it is some floating signal line causing the
> monitor to misdetect activity?

Does the Intel hardware have the capability to switch
the DVI signal lines from high-z to ground during DPMS
suspend, and if so, does the driver do the right thing?
Obviously I have no clue about DVI and intel-gfx, but
I thought to ask anyway.


Johannes