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ThinkPad T480s backlight flicker in Linux?

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Shhhh_Peaceful
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Joined: Sun Aug 28, 2022 3:31 pm
Location: Dublin, Ireland

ThinkPad T480s backlight flicker in Linux?

#1 Post by Shhhh_Peaceful » Sun Aug 28, 2022 3:41 pm

I have a weird issue with my ThinkPad T480s (i5-8250U, no dGPU) in Linux. The issue is that the LCD backlight starts flickering at about 15-20 Hz after the machine wakes up from sleep.

I'm 100% sure that it's not a hardware problem because this never happens under Windows. The worst part is that once it starts flickering, it continues to flicker until I either power off the internal battery in the BIOS setup or reset the machine by inserting a paper clip into the reset hole for 10s. I guess the Intel Linux driver sets some registers in the GPU that persist through reboots.

I did some testing and basically I found that this happens with the Linux kernel 5.17 or later, which means that Ubuntu 22.04 is not affected, but Fedora and Pop!_OS are. Has anybody else had this issue? If yes, have you been able to fix it?

I would be grateful for any tips.
Current: X230 (i5-3380M/16GB/1TB SSD), T480s (i5-8250U/16GB/256GB SSD)
Past: T23, X30, X32, X60

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