Re: kern/57825 (Malfunctioning screen brightness keys and sysctl)

[maya%NetBSD.org@localhost]

The following reply was made to PR kern/57825; it has been noted by GNATS.

From: maya%NetBSD.org@localhost
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/57825 (Malfunctioning screen brightness keys and sysctl)
Date: Mon, 13 May 2024 01:18:22 +0000

 The behaviour where the brightness goes up to 100% when
 plugged/unplugged is not specific to Thinkpad T450 and is probably best
 documented in a separate bug. I tried to have a look at it, and got some
 insights so far:
 
 It looks like there are two ways that the notifications about the key
 being pressed can go.
 
 1. Through ACPI, which is what's happening right now.
 The behaviour of changing brightness when plugged in should be
 configurable (through _DOS), and we do try to do this, but it doesn't
 work for my machine and others.
 
 2. Through the OS, in the NetBSD case that's through pmf(9).
 We haven't taught i915 to listen to pmf notifications and instead relied
 on ACPI so far.
 
 It looks like Linux, on newer machines (advertising support for windows
 8) will explicitly ignore requests for changing brightness from ACPI.
 acpi_video_get_backlight_type() == acpi_backlight_native
 And probably deliver them through something like pmf(9).
 We should probably do the same.