Re: [ibm-acpi-devel] [PATCH] thinkpad_acpi: Add Auto mode support with dynamic max_brightness

[Qiling Zhu <kmatzkaczor244@gmail.com>]

Hi Andrea,

Thanks for the detailed report! I actually noticed that the keyboard
backlight OSD started working in KDE after applying my patches,
whereas it hadn't appeared at all before. I didn't look into it
at the time, so thanks for pointing out the likely reason behind
this behavior.



On Sat, Nov 07, 2026 at 11:11:08PM +0800, Rong Zhang wrote:
> Hi Andrea,
> 
> ...
> 
> +CC Qiling
> 
> Oops, this indeed needs a fix patch for backporting.
> 
> Qiling, while you series will fix this, it may be better to add a fix
> patch CC'ing stable@vger.kernel.org to the very beginning of the series,
> so that the fix can be easily backported.
> 

Thanks, Rong. I'll split out a minimal, self-contained bug fix
before the refactoring and feature addition, as you suggested.

I'm still learning the upstream and stable backporting process,
so I'm wondering whether it would be better to submit the fix
separately or keep it as the first patch of the next revision.
Submitting it separately could get the fix merged and backported
sooner, though I'm not sure how urgent this particular fix is.

I'd appreciate your guidance on which approach would be more
appropriate, and I'm happy to follow your suggestion.

> 
> My opinion:
> 
> If auto mode disables keyboard backlight most of the time, it should
> report 0. For example, when the auto mode if backed by an ALS sensor, it
> should disable keyboard backlight most of the time, because most users
> seldom use the laptop in dark environments.
> 
> Same for proximity- or activity-based control, as it only illuminates
> when the user touches the keyboard.
> 
> The ideapad-laptop driver and Qiling's series have already taken this
> strategy.
> 
> Thanks,
> Rong
> 

I agree that mapping Auto mode to 0 makes more sense. Besides
the reasons you mentioned, the Fn+Space cycle on my ThinkPad
is 0 -> 3 -> 1 -> 2 -> 0, as Andrea also observed on the X9.

Mapping Auto (3) to 2 would make the reported brightness jump
from 0 to 2, then back to 1 and up to 2 again, which seems
rather misleading, especially since Auto mode does not represent
the maximum fixed brightness level.

Regards,
Qiling Zhu