# Backlight flickers with kernel >= 4.6

## hiarcat

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

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

Hi,

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

May be the wrong frequency?

Help welcome   :Very Happy: 

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## Logicien

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

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

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

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

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.

 :Very Happy:   :Very Happy:   :Very Happy: 

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## ExecutorElassus

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

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

thanks, work fine on msi GS70 2QC with debian stretch!

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## hiarcat

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

Hi,

even in 4.7.0 the problem still exists ...

 :Sad: 

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