Public bug reported: When running Ubuntu with linux-image-5.3.0-23-generic, mainline 5.3.13, or latest 5.4+ my Lenovo ThinkPad P1 Gen 2 with a Samsung OLED panel is unable to change the backlight brightness. The buttons trigger the on- screen display and move the bar but the actual display brightness does not change. With the kernel option i915.enable_dpcd_backlight=1 it does make the backlight change but erratically. For example moving through the range you get stuff like off, medium bright, dim, bright, medium, off. This does work in Ubuntu linux-image-4.15.0-1059-oem. It seems the following commits in particular make the difference.
UBUNTU: SAUCE: i915: intel_dp_aux_backlight: Fix max backlight calculations https://git.launchpad.net/~canonical-kernel/ubuntu/+source/linux-oem/+git/eoan/commit/?h=oem&id=ff39163c455f31005e2709a2006a7605b3d8a05f UBUNTU: SAUCE: drm/i915: customize DPCD brightness control for specific panel https://git.launchpad.net/~canonical-kernel/ubuntu/+source/linux-oem/+git/eoan/commit/?h=oem&id=cf7286b44a6e27967f5ed134c4492dd17bde118a It has been explained to me that these OEM changes are unlikely to be directly ported into -generic images but it seems relevant to document the issue. I ported the above commits to the latest linux mainline kernel and am running that (other than while reporting this issue). This was in part because >= 5.3.12 fixes another issue with this hardware where the screen remains black after a resume (https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1854177). I have filed https://bugzilla.kernel.org/show_bug.cgi?id=205699. https://github.com/altendky/linux/commit/395eb4b85f6a0f85061c0598247727de0d9316f6 https://github.com/altendky/linux/commit/c2dc38e6aadf3d979bea83e382a1b119574df7af Built with: git clean -fdx && cp /boot/config-5.3.0-23-generic .config && yes '' | make oldconfig && make clean && make -j `getconf _NPROCESSORS_ONLN` deb- pkg LOCALVERSION=-altendky-backlight Note that the use of DEVICE_ID_ANY is likely bad and the correct ID for this panel should be identified. I wanted to first confirm it worked before bothering to figure out which ID was needed there and how to get it. I have naively ported these patches. While I have done embedded C for years and some hardware design... I am not familiar with Linux kernel development nor any details of controlling this hardware. ProblemType: Bug DistroRelease: Ubuntu 19.10 Package: linux-image-5.3.0-23-generic 5.3.0-23.25 ProcVersionSignature: Ubuntu 5.3.0-23.25-generic 5.3.7 Uname: Linux 5.3.0-23-generic x86_64 ApportVersion: 2.20.11-0ubuntu8.2 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC0: altendky 1381 F.... pulseaudio CurrentDesktop: KDE Date: Thu Nov 28 21:24:12 2019 InstallationDate: Installed on 2019-11-26 (2 days ago) InstallationMedia: Kubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017) MachineType: LENOVO 20QTCTO1WW ProcFB: 0 i915drmfb ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.3.0-23-generic root=/dev/mapper/lvm_group-root ro quiet splash vt.handoff=7 RelatedPackageVersions: linux-restricted-modules-5.3.0-23-generic N/A linux-backports-modules-5.3.0-23-generic N/A linux-firmware 1.183.2 SourcePackage: linux UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 10/17/2019 dmi.bios.vendor: LENOVO dmi.bios.version: N2OET40W (1.27 ) dmi.board.asset.tag: Not Available dmi.board.name: 20QTCTO1WW dmi.board.vendor: LENOVO dmi.board.version: SDK0T08861 WIN dmi.chassis.asset.tag: No Asset Information dmi.chassis.type: 10 dmi.chassis.vendor: LENOVO dmi.chassis.version: None dmi.modalias: dmi:bvnLENOVO:bvrN2OET40W(1.27):bd10/17/2019:svnLENOVO:pn20QTCTO1WW:pvrThinkPadP1Gen2:rvnLENOVO:rn20QTCTO1WW:rvrSDK0T08861WIN:cvnLENOVO:ct10:cvrNone: dmi.product.family: ThinkPad P1 Gen 2 dmi.product.name: 20QTCTO1WW dmi.product.sku: LENOVO_MT_20QT_BU_Think_FM_ThinkPad P1 Gen 2 dmi.product.version: ThinkPad P1 Gen 2 dmi.sys.vendor: LENOVO ** Affects: linux (Ubuntu) Importance: Undecided Status: New ** Tags: amd64 apport-bug eoan -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1854413 Title: Backlight adjustments shows OSD but does not change anything on Samsung OLED panel To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1854413/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
