I enabled the KMS debug messages in the drm module:
$ cat /etc/modprobe.d/drm-debug.conf
options drm debug=0x04
$ sudo update-initramfs -u -k $(uname -r) && sudo reboot
...
Unfortunately, it doesn't look like my device_id is set after the
drm_dp_read_desc() in drm_dp_read_desc:
$ dmesg | grep -i OUI
[ 1.378026] [drm:drm_dp_read_desc [drm_kms_helper]] DP sink: OUI 38-ec-11
dev-ID HW-rev 0.0 SW-rev 0.0 quirks 0x0000
Hopefully the device_id is set for the Dell platform in bug #1856134 so
that commit 3269788061d2 ("USUNTU: SAUCE: drm/i915: Force DPCD backlight
mode on Dell Precision 4K sku") can be more specific to that device.
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You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux-5.4 in Ubuntu.
https://bugs.launchpad.net/bugs/1861521
Title:
[FOCAL][REGRESSION] Intel Gen 9 brightness cannot be controlled
Status in linux-5.4 package in Ubuntu:
Confirmed
Status in linux-5.4 source package in Focal:
Confirmed
Bug description:
After upgrading from Eoan (5.3.0-29.31) to Focal (5.4.0-12.15), I no
longer have the ability to control the backlight brightness on my HP
EliteBook 840 G5. When pressing the brightness hotkeys, the on-screen
indicator pops up and shows that the brightness setting is being
changed but the actual screen brightness is stuck on the lowest
setting.
This laptop has a built-in privacy screen. If I activate the privacy
screen (fn-f2), then the actual screen brightness goes to the maximum
setting and then I am able to dim and brighten the backlight as long
as the privacy screen functionality is turned on.
This is a regression from Eoan's 5.3.0-29.31 kernel where I was able
to control the brightness with and without the privacy screen
functionality being turned on.
ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.4.0-12-generic 5.4.0-12.15
ProcVersionSignature: Ubuntu 5.4.0-12.15-generic 5.4.8
Uname: Linux 5.4.0-12-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu16
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Fri Jan 31 11:42:16 2020
InstallationDate: Installed on 2019-06-24 (221 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
ProcEnviron:
TERM=xterm-256color
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
SourcePackage: linux-signed-5.4
UpgradeStatus: Upgraded to focal on 2020-01-28 (3 days ago)
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