[Intel-gfx] periodic wakeup from DPMS suspend

Alex Deucher alexdeucher at gmail.com
Tue Oct 6 20:04:53 PDT 2015

On Tue, Oct 6, 2015 at 11:10 AM, Johannes Stezenbach <js at sig21.net> wrote:
> Hi,
> 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.
> How can I find out if this is an issue of the NEC monitor
> or the Intel graphics?
> - when I pull the DVI cable the monitor stays in suspend
> - I tried to use drm.debug=6 and ftrace to see if something
>   is periodically accessing DDC or similar, but it didn't
>   reveal anything to me, but then I know nothing about
>   graphics drivers and probably didn't do it right
> I noticed there is some hotplug detection code,
> my initial thought was that this could cause the
> wakeup.  But since the period is somewhat irregular
> maybe it is some floating signal line causing the
> monitor to misdetect activity?
> Currently I'm running 4.2.3, but the same issue
> happens with older kernels, I tried 3.17+.
> Let me know if you have any ideas what to try.

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.


> BTW, in sysfs the output shows up as HDMI-A-2:
> (the board has VGA, DVI, HDMI and DP)
> $ find /sys -name edid
> /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-HDMI-A-1/edid
> /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-HDMI-A-2/edid
> /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-HDMI-A-3/edid
> /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-VGA-1/edid
> /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-1/edid
> /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-2/edid
> /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-3/edid
> Another observation is that the HDMI-A-* outputs don't
> have an i2c node to link the matching DDC channel,
> while the DP outputs have?
> $ grep . /sys/class/i2c-dev/i2c-*/name
> /sys/class/i2c-dev/i2c-0/name:i915 gmbus ssc
> /sys/class/i2c-dev/i2c-1/name:i915 gmbus vga
> /sys/class/i2c-dev/i2c-2/name:i915 gmbus panel
> /sys/class/i2c-dev/i2c-3/name:i915 gmbus dpc
> /sys/class/i2c-dev/i2c-4/name:i915 gmbus dpb
> /sys/class/i2c-dev/i2c-5/name:i915 gmbus dpd
> /sys/class/i2c-dev/i2c-6/name:DPDDC-B
> /sys/class/i2c-dev/i2c-7/name:DPDDC-C
> /sys/class/i2c-dev/i2c-8/name:DPDDC-D
> The monitor brightness can be controlled via
> /dev/i2c-3 with ddccontrol.
> TIA,
> Johannes
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