Bug 351209

Summary:	Brightness setting for "On Battery" works only for a very low brightness level
Product:	[Plasma] Powerdevil	Reporter:	a.pronobis
Component:	general	Assignee:	Plasma Development Mailing List <plasma-devel>
Status:	RESOLVED INTENTIONAL
Severity:	normal	CC:	kde
Priority:	NOR
Version:	5.3.90
Target Milestone:	---
Platform:	Ubuntu
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description a.pronobis 2015-08-12 02:13:49 UTC

After enabling "Screen brightness" control in the "On battery" profile, the brightness when running on battery does not change automatically unless the "Level" is set to a very low value (sth around 10%). For such low value, unplugging AC will indeed affect brightness. If the level is set to any higher value, e.g. 50%, unplugging AC will not affect brightness at all.  Brightness settings for "On AC Power" profile work without problems for any brightness level.

This behavior can be observed using udeavadm monitor, which for the low level value shows for AC unplug event:

KERNEL[2565.602739] change   /devices/pci0000:00/0000:00:02.0/backlight/acpi_video0 (backlight)
UDEV  [2565.604719] change   /devices/pci0000:00/0000:00:02.0/backlight/acpi_video0 (backlight)

If higher level is set, udev only reports setting brightness when plugging IN the AC, but not when unplugging.

Keyboard backlight also does not seem to work for the On Battery profile, while it does work for "On AC power".

Reproducible: Always

Steps to Reproduce:
1. Enable Screen brightness for "On Battery" profile and set the level to 50%
2. Unplug AC
3. Observe that the brightness did not change
4. Plug in AC
5. Set brightness level to around 5%
6. Unplug AC
7. Observe that brightness has been changed

Actual Results:  
As in the steps, brightness is not affected for certain level settings.

Expected Results:  
Brightness should be adjusted no matter what level is set.

Running Ubuntu 15.10 with KDE 5.3.95.

Comment 1 a.pronobis 2015-08-12 02:19:27 UTC

It also seems that the max level for which brightness will still be adjusted depends on the screen brightness when AC is unplugged. Example: If I lower the brightness using Fn keys before unplugging, the brightness will NOT be adjusted even if set to a low level in the settings "On Battery".

Comment 2 Kai Uwe Broulik 2015-08-12 05:04:23 UTC

If the current brightness is lower than the one configured for On Battery, the brightness will not be raised when unplugging AC. This is intended behavior.

Comment 3 a.pronobis 2015-08-12 05:42:09 UTC

In my case it will not be lowered. When I said that there is a dependency between the AC and battery brightness, I meant that AC brightness level has to be sth like 10 times larger than the battery brightness in order for the battery brightness to be changed.