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Backlight flickers with kernel >= 4.6
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hiarcat
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PostPosted: Sat Jun 11, 2016 7:26 am    Post subject: Backlight flickers with kernel >= 4.6 Reply with quote

Hi,

my DELL Inspiron 17 (FHD Display) has a Intel Corporation HD Graphics 5500 (rev 09) GPU. With kernel < 4.6 everything works like a charm!

With kernel >= 4.6 (tested 4.6.0, 4.6.1 and 4.6.2) the backlight of the display flickers (the brightness changes maybe 2 times a second, but not with a constant frequency). I use the same kernel config (cp 4.5.3 -> make menuconfig -> save the config, gentoo-sources).

Is there anyone with the same problem? Is there any solution?

If you need some more info I'll post my kernel config or something else.

Thank you!
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hiarcat
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PostPosted: Sat Jun 25, 2016 10:27 am    Post subject: Reply with quote

Hi,

today I tried gentoo-sources-4.6.3 and the backlight flickers also ...

Is there any change in i915 or in the backlight code?
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hiarcat
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PostPosted: Sat Jun 25, 2016 10:58 am    Post subject: Reply with quote

Hi,

with kernel >= 4.6 there's also a pattern or a moiré pattern ...

May be the wrong frequency?

Help welcome :D
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Logicien
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PostPosted: Sat Jun 25, 2016 12:28 pm    Post subject: Reply with quote

Hi,

you have two different kernel parameters you can test separetely or together. You have the parameter acpi_backlight you can set to acpi_backlight=dell to force the kernel to use specific Dell Acpi support.

You can use i915.invert_brightness too. You are better to read the /usr/src/linux/Documentation/kernel-parameters.txt related description of this parameter to choose the value.

The video module have backlight parameters too.

It's a good idea to setup your kernel configuration to include the Dell options it have.

It may be a kernel version bug.
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hiarcat
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PostPosted: Sat Jun 25, 2016 2:48 pm    Post subject: Reply with quote

Hi Logicien,

thank you!

I've tried both parameters, but the backlight still flickers. And also the moiré pattern is still there.

If I set the xorg.conf to use uxa (instead of sna), I'll get a black screen.

So I use 4.5.3 again ...
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ExecutorElassus
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PostPosted: Sun Jun 26, 2016 4:49 pm    Post subject: Reply with quote

I've been having a similar problem (see my post here), on an MSI laptop with nvidia GPU hardware. Login manager is lightdm and WM is Enlightenment.

Let me know if this is also the case for you: if I move the mouse, the flickering stops. Once the mouse stops, the screen goes back to flickering. Does your laptop do this as well?

It's a weird problem, and I have the same workaround: booting kernel <4.6.* gives a normal screen.

Cheers,

EE
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ExecutorElassus
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PostPosted: Sun Jun 26, 2016 5:28 pm    Post subject: Reply with quote

UPDATE: see this news release, and this bug report, which relate to screen flickering with PSR enabled. This was a new update in the 4.6 kernels. Y'all: can you check booting with i915.psr=0 set in your kernel boot-up, and see if that fixes it?

Soon as my laptop is done with an emerge world update, I'll try it myself and report back.

Cheers,

EE
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hiarcat
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PostPosted: Thu Jun 30, 2016 6:07 pm    Post subject: Reply with quote

Hi ExecutorElassus,

thanks!!!

I solved the problem by setting "i915.enable_psr=0" as kernel command line. "i915.psr=0" doesn't work for me.

:D :D :D
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ExecutorElassus
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PostPosted: Fri Jul 01, 2016 4:06 am    Post subject: Reply with quote

I did the same. Now, there's no flicker, but the screen also doesn't update until I move the mouse (which is super annoying). Anybody else know workarounds to this? It's rendering my laptop more or less unusable.

Cheers,

EE
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hiarcat
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PostPosted: Fri Jul 01, 2016 11:38 am    Post subject: Reply with quote

Hi ExecutorElassus,

only "i915.enable_psr=0" works for me, "i915.enable_psr=2" is completely unusable. With "i915.enable_psr=1" and "i915.enable_psr=3" the backlight flickers.

My screen updates, so everything is fine.

Thank you for the hint!
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katarpilar
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PostPosted: Mon Jul 11, 2016 11:16 am    Post subject: Reply with quote

thanks, work fine on msi GS70 2QC with debian stretch!
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hiarcat
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PostPosted: Tue Jul 12, 2016 5:49 pm    Post subject: Reply with quote

Hi,

also in 4.6.4 I have to set "i915.enable_psr=0".

And ExecutorElassus is right, also my screen freezes when watching full screen videos and the mouse doesn't move.

I hope there will be some further development ...

Bye
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hiarcat
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PostPosted: Sun Jul 31, 2016 4:24 pm    Post subject: Reply with quote

Hi,

even in 4.7.0 the problem still exists ...

:(
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