Hi Nick, I've updated the test plan part. In Beijing Lab, we have several platforms could reproduce this issue.
Hi Mario, How could we confirm AMD laptop supports custom brightness curve (look in kernel log)? From the 'backlight' keyword, I only got these logs below. $ sudo dmesg | grep backlight [ 1.600606] thinkpad_acpi: This ThinkPad has standard ACPI backlight brightness control, supported by the ACPI video driver [ 1.665703] systemd[1]: Created slice system-systemd\x2dbacklight.slice - Slice /system/systemd-backlight. [ 1.667804] systemd[1]: Starting systemd-backlight@leds:tpacpi::kbd_backlight.service - Load/Save Screen Backlight Brightness of leds:tpacpi::kbd_backlight... [ 1.674453] systemd[1]: Finished systemd-backlight@leds:tpacpi::kbd_backlight.service - Load/Save Screen Backlight Brightness of leds:tpacpi::kbd_backlight. ** Description changed: [Impact] At shutdown time systemd will record the most recently used brightness value and then attempt to restore it the next boot. In order to do this; it currently will read the 'actual_brightness' value and use that to save. This normally works fine; but GPU drivers don't always show the same value in 'brightness' and 'actual_brightness' meaning that the wrong value may be restored the next boot. This problem is very prominently found on AMD APUs starting with kernel 6.15 due to a new feature called "custom brightness curves". Custom brightness curves are brightness values programmed by an OEM in the firmware to make the panel behave optimally. The 'actual_brightness' of some 'brightness' values will be lower. The same issue can occur on systems using "panel power savings" which behaves similarly. For example if the brightness a user requested was 150, the actual_brightness might be 130. So the next boot the brightness will be "set" to 130, but the actual brightness might be 115. If the user reboots again it will be set to 115 for the next boot but the actual brightness might be 100. That is this gets worse and worse each reboot cycle until the system eventually boots up at minimum brightness. [Test Plan] Verify brightness save/restore works properly on Intel UMA, AMD UMA, and either I+N or A+N systems. + 0. Use a laptop with an eDP panel, AMD laptop that supports custom + brightness curve (look in kernel log) + + 1. Look at value of brightness for device in /sys/class/backlight/. Note it down. + $ grep . /sys/class/backlight/*/* 2>/dev/null + + 2. Unplug the power supply, look at the value of brightness again. The + actual_brightness will be decreased on AMD laptops that supportes custom + brightnes curve. + + 3. Reboot without power supply, look at value again, ensure the + actual_brightnesss and brightness are the same. + + [Where problems could occur] If a driver relies upon actual_brightness rather than brightness (which is against kernel API [1] then the brightness might no longer be saved and restored properly. [1] https://origin.kernel.org/doc/html/next/admin-guide/abi- stable.html#abi-sys-class-backlight-backlight-actual-brightness [Other Info] This has been fixed in upstream systemd in this commit: https://github.com/systemd/systemd/commit/9a224c307b36610e3675390eb2620e74d0f4efb0 It's been brought into stable systemd releases carried by other distros as well. No regressions have been reported upstream that I'm aware of. ** Description changed: [Impact] At shutdown time systemd will record the most recently used brightness value and then attempt to restore it the next boot. In order to do this; it currently will read the 'actual_brightness' value and use that to save. This normally works fine; but GPU drivers don't always show the same value in 'brightness' and 'actual_brightness' meaning that the wrong value may be restored the next boot. This problem is very prominently found on AMD APUs starting with kernel 6.15 due to a new feature called "custom brightness curves". Custom brightness curves are brightness values programmed by an OEM in the firmware to make the panel behave optimally. The 'actual_brightness' of some 'brightness' values will be lower. The same issue can occur on systems using "panel power savings" which behaves similarly. For example if the brightness a user requested was 150, the actual_brightness might be 130. So the next boot the brightness will be "set" to 130, but the actual brightness might be 115. If the user reboots again it will be set to 115 for the next boot but the actual brightness might be 100. That is this gets worse and worse each reboot cycle until the system eventually boots up at minimum brightness. [Test Plan] Verify brightness save/restore works properly on Intel UMA, AMD UMA, and either I+N or A+N systems. 0. Use a laptop with an eDP panel, AMD laptop that supports custom brightness curve (look in kernel log) 1. Look at value of brightness for device in /sys/class/backlight/. Note it down. $ grep . /sys/class/backlight/*/* 2>/dev/null 2. Unplug the power supply, look at the value of brightness again. The actual_brightness will be decreased on AMD laptops that supportes custom brightnes curve. 3. Reboot without power supply, look at value again, ensure the - actual_brightnesss and brightness are the same. - + actual_brightnesss and brightness are the same with the ones before + reboot. [Where problems could occur] If a driver relies upon actual_brightness rather than brightness (which is against kernel API [1] then the brightness might no longer be saved and restored properly. [1] https://origin.kernel.org/doc/html/next/admin-guide/abi- stable.html#abi-sys-class-backlight-backlight-actual-brightness [Other Info] This has been fixed in upstream systemd in this commit: https://github.com/systemd/systemd/commit/9a224c307b36610e3675390eb2620e74d0f4efb0 It's been brought into stable systemd releases carried by other distros as well. No regressions have been reported upstream that I'm aware of. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2110585 Title: [SRU] Stop using 'actual_brightness' in systemd To manage notifications about this bug go to: https://bugs.launchpad.net/oem-priority/+bug/2110585/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
