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Latest kernel update broke screen brightness

Just posting this for anyone who runs into this issue. After the last update to kernel-4.15.17 my screen brightness stopped working on my msi gt70 with intel nvidia optimus. Reverting to the 4.15.16 kernel fixes the issue. I'm posting this in case anyone runs across this or knows of any bugs already filed with this issue, or of any solutions.

Happened to me as well. You can fix it by adding the kernel parameter, "acpi_backlight=vendor" but for me, max brightness wasn't nearly as bright as the display could go. You might have better results though. Feel free to try it if you'd like.

Thank you for the reply. I meant to post my trials and errors sooner. I had already included that in my config from a long time ago. With this latest update i've tried removing it all together as well as these other variations. Maybe one of these other variations will do better for you than they did for me.

acpi_backlight=video
acpi_backlight=vendor
acpi_backlight=native

For now, i'm just booting into the older kernel. Let me know if you read anything else on the topic. I thought i read that it was a known issue with this kernel update and optimus laptops, but i wasn't sure if the thread i was reading was talking about this latest update or another one. Thanks again. I'm crossing my fingers it just magically fixes in the next update. :) As a side note, I wonder what would happen if you boot into the old kernel, turn up the brightness all the way, then boot into the new kernel. Does it stay bright and give you back full brightness control with your modification? My thoughts are along the line of maybe some type of calibration or a power starting point to reference when the commands adjust the power settings (that's essentially what is happening in think). Just a thought.

UPDATE: The following kernel update fixed my screen brightness. It has returned to normal. Just thought I'd post so people know. I kept my boot kernel at the older one until this was fixed. Kernel where it started working again and that I'm back to running is

4.16.7-100.fc26.x86_64

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