Bug 194675

Summary:	Backlight settings doesn’t work until the screen goes black due to inactivity or lid close, neither does systems goes into PC6
Product:	Power Management	Reporter:	Bruno Pagani (bruno.n.pagani)
Component:	Other	Assignee:	Lv Zheng (lv.zheng)
Status:	CLOSED UNREPRODUCIBLE
Severity:	normal	CC:	rui.zhang
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	4.6+	Subsystem:
Regression:	No	Bisected commit-id:

Description Bruno Pagani 2017-02-23 10:22:46 UTC

Since I’ve started running 4.6 on my main laptop (but still valid with 4.9.11, and I suspect 4.10 that I should be able to test soon), I have an issue with backlight on boot: setting the screen brightness has no effect (and neither does systemd restoring previous setting, the brightness is remaining at max value in both cases) and the system never goes into PC6.

That goes away once the screen goes black at least once, whether that would be because of inactivity (my DE, KDE Plasma, is set to turns the screen black if nothing happens in the while) or because of a lid close/open cycle (the screen goes black when closing the lid).

This is a Dell XPS 9530, with Core i7 4702-HQ and Intel Graphics 4600HD. Latest available BIOS/EFI installed (A09).

Comment 1 Zhang Rui 2017-02-27 07:08:36 UTC

(In reply to Bruno Pagani from comment #0)
> Since I’ve started running 4.6 on my main laptop (but still valid with
> 4.9.11, and I suspect 4.10 that I should be able to test soon), I have an
> issue with backlight on boot: setting the screen brightness has no effect

what do you do to set the screen brightness?
please attach the output of “grep . /sys/class/backlight/*/*”.

> (and neither does systemd restoring previous setting, the brightness is
> remaining at max value in both cases) and the system never goes into PC6.
> 
> That goes away once the screen goes black at least once, whether that would
> be because of inactivity (my DE, KDE Plasma, is set to turns the screen
> black if nothing happens in the while) or because of a lid close/open cycle
> (the screen goes black when closing the lid).
> 
> This is a Dell XPS 9530, with Core i7 4702-HQ and Intel Graphics 4600HD.
> Latest available BIOS/EFI installed (A09).

Comment 2 Zhang Rui 2017-03-20 04:19:57 UTC

ping...

Comment 3 Bruno Pagani 2017-03-20 06:52:16 UTC

Sorry for the delay, I’m currently travelling in a foreign country without the affected laptop.

But the answer to your question is that I use the Fn keys to set the values. But modifying /sys/class/backlight/intel_backlight/brightness has the same effect (using the Fn keys affects this value one way or one other).

I should add that when it works again, it immediately switches to the value that has been set in the first step.

So for instance if I boot, screen brightness is at maximum, then I set it to half but nothing happens, then I close and reopen LID, and then screen brightness is at half maximum and setting it to another value does work.

I shall be in possession of the affected laptop by mid-April for more debug log/testing as required.

Comment 4 Zhang Rui 2017-06-17 07:48:08 UTC

ping...

Comment 5 Bruno Pagani 2017-06-19 10:33:29 UTC

I forgot about this when I came back… I don’t have the laptop at hand right now, I’m not sure I’ll be able to get to it before 3 weeks. But I’ve put a reminder on this time. ;)

Comment 6 Zhang Rui 2017-06-20 02:38:49 UTC

Okay, then I will mark this bug as closed temporarily.
Please feel free to re-open it when you have the laptop on hand and can provide the information required.
BTW, please do confirm the problem still exists in latest upstream kernel before you do the test.