Advice needed on how to troubleshoot a video problem when resuming from sleep

aragorn2101 · 05-29-2017, 01:03 AM

Are there any other files in /sys/class/backlight/samsung/ ?

If not, do you happen to have a directory "samsung" deep under /sys/devices for the LCD backlight like what we have for intel_backlight?

hazel · 05-29-2017, 05:49 AM

/sys/class/backlight/samsung is actually a symbolic link to /sys/devices/platform/samsung/backlight/samsung. There are several files in there: the backlight-specific ones are brightness, max_brightness, actual_brightness, and bl_power. Brightness is editable: the default levels seem to be 1 for battery operation and 8 for AC power. Actual_brightness is read-only and always equal to brightness. Max_brightness is 8 and also read-only as you would expect. I have no idea what bl_power does, but the value when the system is on charge is 0.

Edit: I just googled and found this:
# Turn off backlight
echo 1 | sudo tee /sys/class/backlight/*/bl_power

# Turn on backlight
echo 0 | sudo tee /sys/class/backlight/*/bl_power

I'm going to try some experiments with this.

hazel · 05-29-2017, 06:56 AM

Nope, that isn't it. Getting the hook script to echo 0 into bl_power doesn't switch the screen on; the trace shows that it was already set to 0.

aragorn2101 · 05-30-2017, 08:00 AM

I think file /sys/devices/platform/samsung/backlight/samsung/brightness should be monitored closely. It is the equivalent file which I use to change brightness in the tty's for intel_backlight. If this does not work I really don't know any other way.

hazel · 05-31-2017, 11:30 AM

I wrote this script and put it in /etc/pm/sleep.d:

Code:

#! /bin/bash
br=`cat /sys/devices/platform/samsing/backlight/samsung/actual_brightness`
p=`cat /sys/devices/platform/samsing/backlight/samsung/bl_power`
case $1 in
     suspend|hibernate)
          echo "Going to sleep..." >> /root/backlight
          echo "Brightness is $br" >> /root/backlight
          echo "Power setting is $p" >> /root/backlight;;
     resume|thaw)
          echo "Waking up..." >> /root/backlight
          echo "Brightness is $br" >> /root/backlight
          echo "Power setting is $p" >> /root/backlight;;
esac
exit 0

What I got was:

Going to sleep...
Brightness is 1
Power setting is 0
Waking up...
Brightness is 1
Power setting is 0

So everything is the same after waking as it was before going to sleep. It was a nice theory but it doesn't seem to be correct.

aragorn2101 · 06-01-2017, 06:02 AM

Quote:

Originally Posted by hazel

So everything is the same after waking as it was before going to sleep. It was a nice theory but it doesn't seem to be correct.

Yeah, was a nice theory though. Have to rule out solving it using backlight values then. Maybe it's something deeply rooted in viafb.

hazel · 06-01-2017, 06:31 AM

Quote:

Originally Posted by aragorn2101

Yeah, was a nice theory though. Have to rule out solving it using backlight values then. Maybe it's something deeply rooted in viafb.

That's why I'll now have to try out all the combinations of video quirks that pm-utils provides. But it's disheartening, repetitive work so I can only do it in small sessions. If I find a combo that works, I'll post it here.

Meanwhile I have found a new riddle, so expect another thread.