Created attachment 289781 [details] dmesg Latest amdgpu driver will check is_dmcu_initialized, if yes, call dmcu_set_backlight_level to set backlight via register BL1_PWM_USER_LEVEL. When issues occur, the value is set correctly, even readout. But the backlight is not changed. The backlight can be changed after reboot from windows if installed dual OS(Windows10 and Linux). It can be reproduced by S3 in Linux. I can hack the code to force using driver instead of dmcu, then backlight can be changed. Latest amdgpu firmware from linux-firmware git is tested, no luck.
edid-decode (hex): 00 ff ff ff ff ff ff 00 0d ae 88 13 00 00 00 00 0e 1c 01 04 a5 1d 11 78 02 ee 95 a3 54 4c 99 26 0f 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 b4 3b 80 4a 71 38 34 40 30 20 36 00 25 a5 10 00 00 18 00 00 00 fe 00 4e 31 33 33 48 43 45 2d 45 4e 32 0a 20 00 00 00 fe 00 43 4d 4e 0a 20 20 20 20 20 20 20 20 20 00 00 00 fe 00 4e 31 33 33 48 43 45 2d 45 4e 32 0a 20 00 fa ---------------- EDID version: 1.4 Manufacturer: CMN Model 5000 Serial Number 0 Made in week 14 of 2018 Digital display 8 bits per primary color channel DisplayPort interface Maximum image size: 29 cm x 17 cm Gamma: 2.20 Supported color formats: RGB 4:4:4 First detailed timing includes the native pixel format and preferred refresh rate Color Characteristics Red: 0.6396, 0.3300 Green: 0.2998, 0.5996 Blue: 0.1503, 0.0595 White: 0.3134, 0.3291 Established Timings I & II: none Standard Timings: none Detailed mode: Clock 152.840 MHz, 293 mm x 165 mm 1920 1968 2000 2250 ( 48 32 250) 1080 1083 1089 1132 ( 3 6 43) -hsync -vsync VertFreq: 60.008 Hz, HorFreq: 67.929 kHz Alphanumeric Data String: N133HCE-EN2 Alphanumeric Data String: CMN Alphanumeric Data String: N133HCE-EN2 Checksum: 0xfa
You need this patch: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=14ed1c908a7a623cc0cbf0203f8201d1b7d31d16
Created attachment 289843 [details] dmesg-5.8rc2 Hi Alex, Thanks for your quick response. The first kernel dmesg already has that commit. The new pull kernel tree 5.8-rc2+ doesn't work too. dmesg uploaded.
https://lore.kernel.org/lkml/20200708081622.3109902-1-aaron.ma@canonical.com/T/#u upstream a fix.