Ubuntu
linux package

Backlight adjustment doesn't work on Google Pixel Slate

Bug #1895615 reported by satmandu on 2020-09-15

This bug affects 1 person

Affects		Status	Importance	Assigned to	Milestone
	linux (Ubuntu)	Confirmed	Undecided	Unassigned

Bug Description

The Pixel Slate/nocturne backlight does not work due to DPCD logic not identifying the DPCD backlight connection since there is no PWM on the nocturne or eve devices.

ChromeOS documentation of disconnected PWM: https://chromium-review.googlesource.com/c/chromiumos/overlays/board-overlays/+/1171922

Discussion of issue & solution: https://github.com/EmbeddedAndroid/linux-eve/issues/2#issuecomment-561382927

This can be fixed with a simple patch which I have applied successfully to mainline 5.9-rc5: https://gist.github.com/satmandu/d6c2192f66cd14525049fd34d356d71d

Luckily the Ubuntu kernel patches set i915.enable_psr=0 which keeps Panel Self Refresh from dimming the backlight at boot, but that isn't even needed for this device once the backlight is hooked up correctly.

(As a bonus the keyboard backlight also starts working properly at boot.)

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: linux-image-lowlatency 5.8.0.18.22
ProcVersionSignature: Ubuntu 5.8.0-18.19-lowlatency 5.8.4
Uname: Linux 5.8.0-18-lowlatency x86_64
ApportVersion: 2.20.11-0ubuntu45
Architecture: amd64
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
CasperMD5CheckResult: skip
Date: Mon Sep 14 23:52:45 2020
InstallationDate: Installed on 2020-08-24 (21 days ago)
InstallationMedia: Ubuntu 20.10 "Groovy Gorilla" - Alpha amd64 (20200728)
Lsusb:
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 18d1:5030 Google Inc. Hammer
Bus 001 Device 002: ID 8087:0a2a Intel Corp. Bluetooth wireless interface
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: Google Nocturne
ProcEnviron:
TERM=xterm-256color
PATH=(custom, no user)
LANG=en_US.UTF-8
SHELL=/bin/bash
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.8.0-18-lowlatency root=UUID=90e26b2a-aaad-4576-8e90-1962b97d4e96 ro fsck.repair=yes fsck.mode=force
PulseList:
Error: command ['pacmd', 'list'] failed with exit code 1: Home directory not accessible: Permission denied
No PulseAudio daemon running, or not running as session daemon.
RelatedPackageVersions:
linux-restricted-modules-5.8.0-18-lowlatency N/A
linux-backports-modules-5.8.0-18-lowlatency N/A
linux-firmware 1.190
SourcePackage: linux
StagingDrivers: ipu3_imgu
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 06/04/2019
dmi.bios.release: 4.0
dmi.bios.vendor: coreboot
dmi.bios.version: Google_Nocturne.10984.90.0
dmi.board.name: Nocturne
dmi.board.vendor: Google
dmi.board.version: 1.0
dmi.chassis.type: 3
dmi.chassis.vendor: Google
dmi.ec.firmware.release: 0.0
dmi.modalias: dmi:bvncoreboot:bvrGoogle_Nocturne.10984.90.0:bd06/04/2019:br4.0:efr0.0:svnGoogle:pnNocturne:pvr1.0:rvnGoogle:rnNocturne:rvr1.0:cvnGoogle:ct3:cvr:
dmi.product.family: Google_Nocturne
dmi.product.name: Nocturne
dmi.product.version: 1.0
dmi.sys.vendor: Google

Tags:

Revision history for this message

satmandu (satadru-umich) wrote on 2020-09-15:

AlsaInfo.txt Edit (5.6 KiB, text/plain; charset="utf-8")
CRDA.txt Edit (3.0 KiB, text/plain; charset="utf-8")
CurrentDmesg.txt Edit (71.6 KiB, text/plain; charset="utf-8")
Dependencies.txt Edit (2.9 KiB, text/plain; charset="utf-8")
IwConfig.txt Edit (578 bytes, text/plain; charset="utf-8")
Lspci.txt Edit (27.2 KiB, text/plain; charset="utf-8")
Lspci-vt.txt Edit (1.8 KiB, text/plain; charset="utf-8")
Lsusb-t.txt Edit (630 bytes, text/plain; charset="utf-8")
Lsusb-v.txt Edit (21.4 KiB, text/plain; charset="utf-8")
ProcCpuinfo.txt Edit (5.7 KiB, text/plain; charset="utf-8")
ProcCpuinfoMinimal.txt Edit (1.4 KiB, text/plain; charset="utf-8")
ProcInterrupts.txt Edit (3.6 KiB, text/plain; charset="utf-8")
ProcModules.txt Edit (9.7 KiB, text/plain; charset="utf-8")
RfKill.txt Edit (112 bytes, text/plain; charset="utf-8")
UdevDb.txt Edit (210.2 KiB, text/plain; charset="utf-8")
WifiSyslog.txt Edit (103.9 KiB, text/plain; charset="utf-8")
acpidump.txt Edit (152.4 KiB, text/plain; charset="utf-8")

DPCD Backlight enablement for Google nocturne (and possibly Google eve device as well.) Edit (980 bytes, text/plain)

Ubuntu Foundations Team Bug Bot (crichton) on 2020-09-15

tags:

added: patch

Revision history for this message

Ubuntu Kernel Bot (ubuntu-kernel-bot) wrote on 2020-09-15: Status changed to Confirmed

This change was made by a bot.

Changed in linux (Ubuntu):
status:	New → Confirmed

Revision history for this message

Alex Hung (alexhung) wrote on 2020-09-22:

It is a good idea to send your patch to below kernel's mailing lists so this can be reviewed by broader audiences to confirm it will work in all scenario.

INTEL DRM DRIVERS (excluding Poulsbo, Moorestown and derivative chipsets)
M: Jani Nikula <email address hidden>
M: Joonas Lahtinen <email address hidden>
M: Rodrigo Vivi <email address hidden>
L: <email address hidden>

Note: you can also run kernel script "./scripts/get_maintainer.pl dpcd59.patch" for all parties who will be interested in this patch.

You can also include "Cc: <email address hidden>" in your patch so it will be included to previous stable kernels (see https://www.kernel.org/doc/Documentation/process/stable-kernel-rules.rst)

Revision history for this message

satmandu (satadru-umich) wrote on 2020-09-23:

Thanks! I've submitted a version to intel-gfx mailing list as [RFC PATCH 1/1] Remove DPCD Aux Backlight Control PWM_PIN check after discussions with Redhat's Lyude Paul.

https://lists.freedesktop.org/archives/intel-gfx/2020-September/248938.html