I noticed that upstream v5.4.18 allowed me to adjust my screen brightness while Ubuntu-5.4-5.4.0-14.17 does not, which indicates an Ubuntu SAUCE patch as the culprit. I bisected between the two kernels and this was the result:
$ git bisect good 3269788061d24e316633165608259de1c110b801 is the first bad commit commit 3269788061d24e316633165608259de1c110b801 Author: AceLan Kao <[email protected]> Date: Thu Dec 12 17:07:44 2019 +0800 USUNTU: SAUCE: drm/i915: Force DPCD backlight mode on Dell Precision 4K sku BugLink: https://bugs.launchpad.net/bugs/1856134 This platform using DPCD aux to control backlight, so adding the first 3 OUI bytes to the quirk. Signed-off-by: AceLan Kao <[email protected]> Signed-off-by: Seth Forshee <[email protected]> :040000 040000 5eb20635c698b49ae34aece26e3ee9f24631ca72 0a3389d202d1306745004ff8837731f2ceda317e M drivers I'm no expert in this area but it looks to me like that commit is being too generic and a more specific device_id is needed to target that Dell device. Here's the information on my panel: $ edid-decode /sys/class/drm/card0-eDP-1/edid edid-decode (hex): 00 ff ff ff ff ff ff 00 26 cf 7f 05 00 00 00 00 00 1b 01 04 a5 1f 11 78 0a 1d 39 a7 50 47 97 27 13 4f 54 00 00 00 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 60 6d 80 c8 70 38 14 40 18 30 a5 00 35 ae 10 00 00 19 00 00 00 fe 00 4d 31 34 30 4e 56 46 37 20 52 30 20 0a 00 00 00 03 00 04 30 ff 05 3c 9d 2b 14 39 9d 00 00 00 00 00 00 03 00 06 18 ff 0f 3c 3b 2a 0b 39 3b 01 01 00 00 ad ---------------- EDID version: 1.4 Manufacturer: IVO Model 1407 Serial Number 0 Made in year 2017 Digital display 8 bits per primary color channel DisplayPort interface Maximum image size: 31 cm x 17 cm Gamma: 2.20 Supported color formats: RGB 4:4:4, YCrCb 4:4:4 First detailed timing includes the native pixel format and preferred refresh rate Color Characteristics Red: 0.6523, 0.3134 Green: 0.2802, 0.5908 Blue: 0.1523, 0.0771 White: 0.3105, 0.3291 Established Timings I & II: none Standard Timings: none Detailed mode: Clock 280.000 MHz, 309 mm x 174 mm 1920 1944 1992 2120 ( 24 48 128) 1080 1090 1095 1100 ( 10 5 5) -hsync -vsync VertFreq: 120.069 Hz, HorFreq: 132.075 kHz Alphanumeric Data String: M140NVF7 R0 Manufacturer-Specified Display Descriptor (0x03): 00 03 00 04 30 ff 05 3c 9d 2b 14 39 9d 00 00 00 ....0..<.+.9.... Manufacturer-Specified Display Descriptor (0x03): 00 03 00 06 18 ff 0f 3c 3b 2a 0b 39 3b 01 01 00 .......<;*.9;... Checksum: 0xad ** Changed in: linux-5.4 (Ubuntu Focal) Assignee: (unassigned) => AceLan Kao (acelankao) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1861521 Title: [FOCAL][REGRESSION] Intel Gen 9 brightness cannot be controlled To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-5.4/+bug/1861521/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
