Bug 99126 - [945GME] wrong scale for backlight with Xfce
Summary: [945GME] wrong scale for backlight with Xfce
Status: NEEDINFO
Alias: None
Product: xorg
Classification: Unclassified
Component: Driver/intel (show other bugs)
Version: unspecified
Hardware: x86 (IA32) Linux (All)
: medium normal
Assignee: Chris Wilson
QA Contact: Intel GFX Bugs mailing list
URL:
Whiteboard:
Keywords:
Depends on:
Blocks:
 
Reported: 2016-12-17 15:39 UTC by Rpnpif
Modified: 2017-03-08 17:47 UTC (History)
3 users (show)

See Also:
i915 platform: I945GM
i915 features: display/backlight


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Description Rpnpif 2016-12-17 15:39:02 UTC
The scale of change of the intensity of the backlight is wrong.
Changing this is done with the hot keys to increase or decrease.

The minimum get a black screen.
cat /sys/class/backlight/eeepc/brigthness
0
cat /sys/class/backlight/intel_backlight/brigthness
0

1st press on the hot key : get also a black screen.
cat /sys/class/backlight/eeepc/brigthness
1
cat /sys/class/backlight/intel_backlight/brigthness
79787

2nd press : get a medium intensity.
cat /sys/class/backlight/eeepc/brigthness
2
cat /sys/class/backlight/intel_backlight/brigthness
159374

3rd to 12th press get a normal change of the backlight.
To : 796875
But the intensity of the 12th is less than the 11th.

Expected :
The minimum should not light off the screen.
/sys/class/backlight/intel_backlight/brigthness
159374
>From /sys/class/backlight/eeepc/brigthness=1 to 10 or 12, the backlight 
should change linearly without light off.

This buggy behaviour was seen only with Xfce, not with lightdm or the Linux 
console.

Chipset: 945GME
Architecture: X86
Found in version xserver-xorg-video-intel/2:2.99.917+git20161105-1~bpo8+1 from Debian Jessie-backports.
Works fine with older versions.

Machine:Eeepc 901.
Reproducible : always.

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=846882
Comment 2 Jani Nikula 2016-12-19 10:38:38 UTC
(In reply to Rpnpif from comment #0)
> The scale of change of the intensity of the backlight is wrong.
> Changing this is done with the hot keys to increase or decrease.

> This buggy behaviour was seen only with Xfce, not with lightdm or the Linux 
> console.

Please reproduce using *only* /sys/class/backlight/intel_backlight/brigthness directly.
Comment 3 Ricardo 2017-03-03 17:11:18 UTC
Rpnpif please review Jani's suggestion and retest, we need your collaboration in order to continue with this issue. 

If there is not activity from the submitter the bug will be closed. However if you can reproduce the issue attach log and set the status of the bug to reopen
Comment 4 Rpnpif 2017-03-03 20:17:29 UTC
(In reply to Ricardo from comment #3)
> Rpnpif please review Jani's suggestion and retest, we need your
> collaboration in order to continue with this issue. 

Yes, Ricardo. Il will see that in some few days after reinstalling the new release.

Regards.
Comment 5 Ricardo 2017-03-03 20:21:05 UTC
Great, thanks
Comment 6 Rpnpif 2017-03-05 10:29:19 UTC
On my Asus 901 system,
Here are the values of /sys/class/backlight/intel_backlight/brigthness for each pressure on the function key to increase the backlight brightness on Xfce.

79664   : The backlight is yet off instead of a minimum brightness.
159324
239008
318648
398399
477972
557674
637296
716999
796798  : The brightness is maximum
796798  : a new last pressing on the key does not change the value but the seen brightness is less high than the previous pressure. It should be the same.
Other pressures does not change the brightness that remain to a not maximum value instead to be maximum as that it should be.

On the lightdm screen, all work fine.

Perhaps, Xfce use /sys/class/backlight/eeepc/brigthness and lightdm use /sys/class/backlight/intel_backlight/brigthness. I do not known but the scale should be the same.

I conclude that there is a kind of scale issue.

Regards.
Comment 7 Rpnpif 2017-03-05 10:39:01 UTC
Oups, I see now that I did not answer to the question of Jany.

I can say Yes, all work fine using directly /sys/class/backlight/intel_backlight/brigthness.

With
echo value > /sys/class/backlight/intel_backlight/brigthness
with a value between about 80000 and 796876.

Regards.
Comment 8 Jani Nikula 2017-03-07 10:23:34 UTC
What does 'cat /sys/class/backlight/eeepc/type' say?
Comment 9 Rpnpif 2017-03-07 14:40:38 UTC
(In reply to Jani Nikula from comment #8)
> What does 'cat /sys/class/backlight/eeepc/type' say?

platform
Comment 10 Jani Nikula 2017-03-07 17:54:22 UTC
How does /sys/class/backlight/eeepc/brightness work when used directly? Do all values work as expected? The userspace should prefer the platform type backlight interfaces over raw type that intel_backlight is.
Comment 11 Rpnpif 2017-03-08 15:50:05 UTC
(In reply to Jani Nikula from comment #10)
> How does /sys/class/backlight/eeepc/brightness work when used directly? Do
> all values work as expected? The userspace should prefer the platform type
> backlight interfaces over raw type that intel_backlight is.

Yes and no, as I said previouly: 

Before the last release of xserver-xorg-video-intel:
When I press on the hotkey to increase the brightness, the values in /sys/class/backlight/eeepc/brightness increased with a step of 2 (0, 2, 4, ..., 15).
The brightness changed from low value but without a light off screen, to a maximum as expected. All changes of brightness are proportional of the value of the brightness parameter as expected.

With the last release of xserver-xorg-video-intel:
When I press on the hotkey to change the brightness, the values in /sys/class/backlight/eeepc/brightness increase with a step of 1 (0, 1, 2, 3, ..., 15).
The 0 or 1 values get a light off screen.
The 15 value has a strange behaviour. When 15 value is reached the brightness is at the maximum. But a new press on the increasing hotkey get a few lower brightness without change of the 15 value. The following press of the increasing hotkey does not change anything but does not get the brightness maximum.

The decreasing hotkey has the same effect but on a reverse order, obviously.
Comment 12 Jani Nikula 2017-03-08 16:14:57 UTC
(In reply to Jani Nikula from comment #10)
> How does /sys/class/backlight/eeepc/brightness work when used directly?

The key word here was *directly*. That is, if you echo values directly to the sysfs attribute, and do not use hotkeys.

I understand for you this is an overall system and user experience issue. For me it's very much about identifying the component where the problem lies.
Comment 13 Jani Nikula 2017-03-08 16:17:14 UTC
(In reply to Rpnpif from comment #0)
> Found in version xserver-xorg-video-intel/2:2.99.917+git20161105-1~bpo8+1
> from Debian Jessie-backports.
> Works fine with older versions.
Comment 14 Rpnpif 2017-03-08 17:47:57 UTC
(In reply to Jani Nikula from comment #12)
> The key word here was *directly*. That is, if you echo values directly to
> the sysfs attribute, and do not use hotkeys.

Sorry, I understand now.

echo value to /sys/class/backlight/eeepc/brigthness works fine.
The brightness is more or less proportional to the value between 0 to 7 or 8. Between 8 to 15, the increasing is lighter. Zero does not light off the screen.
This is really different that the hotkeys do.

The hotkeys change the brightness **and** the value but the effect on the level of the real brightness is really different.

Thanks for your work.


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