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Kernel 4.12 breaks backlight brightness control
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botinok
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Joined: 29 Jun 2015
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PostPosted: Mon Oct 09, 2017 3:39 pm    Post subject: Kernel 4.12 breaks backlight brightness control Reply with quote

Hi.

After the recent system update I had noticed that backlight control keys don't work so I've switched back to the old kernel and found out that backlight controls are working well.

I tried two recent stable versions from the Gentoo upstream: 4.12.5 and 4.12.12 - they both break backlight control. My current kernel version (with that one everything works fine) is 4.9.34.
The kernels are compiled with oldefconfig and backlight support is enabled with the generic driver.

Though, xbacklight works with these new kernels and there are acpi_video0 and acpi_video1 in /sys/class/backlight/ , but it's not a solution for me.

I'm wondering is it only the 4.12 kernel tree issue? Or maybe the problem somewhere else?
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Hu
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Joined: 06 Mar 2007
Posts: 13831

PostPosted: Tue Oct 10, 2017 12:55 am    Post subject: Reply with quote

There are 44230 git commits present in v4.12.5 that are absent in v4.9.34. If switching to a 4.9.x kernel reliably fixes this for you, then that would suggest that one of those commits is responsible for the observed regression. Can you narrow down where it broke? Is v4.12 bad? Is v4.11? etc.
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