https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #1 from Michel Dänzer (michel@daenzer.net) --- Please attach the output of dmesg.

https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #3 from Lukáš Krejčí (lskrejci@gmail.com) --- Commit 262485a50fd4 ("drm/amd/display: Expand dc to use 16.16 bit backlight") changed the value that is returned for `actual_brightness`:

-static unsigned int dce_abm_get_current_backlight_8_bit(struct abm *abm) +static unsigned int dce_abm_get_current_backlight(struct abm *abm) { struct dce_abm *abm_dce = TO_DCE_ABM(abm); unsigned int backlight = REG_READ(BL1_PWM_CURRENT_ABM_LEVEL);

- return (backlight >> 8); + /* return backlight in hardware format which is unsigned 17 bits, with + * 1 bit integer and 16 bit fractional + */ + return backlight; }

I could not find anything official about the range of `actual_brightness`, only the following blog says that is has to be in range of `brightness`: https://nikula.org/~jani/backlight/#index3h3

I guess amdgpu_dm_backlight_get_brightness() could be changed to bring the `actual_brightness` value in range of `brightness` again since it returns the value of `brightness` in the error path anyway.

https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #5 from Sandor Ecker (esanya@freemail.hu) --- Would it be possible to set max_brightness to 2^16-1 ?

https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #7 from Sandor Ecker (esanya@freemail.hu) --- I have upgraded to 5.6.rc1:

uname -a Linux Aspire-A315-41 5.6.0-050600rc1-generic #202002092032 SMP Mon Feb 10 01:36:50 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

I have seen that the code has log messages like:

DC_LOG_BACKLIGHT("New Backlight level: %d (0x%X)\n", backlight_pwm_u16_16, backlight_pwm_u16_16);

I have set the kernel log by

echo "8" > /proc/sys/kernel/printk cat /proc/sys/kernel/printk 8 4 1 7

but I can't see any logmessage with "New Backlight" in the output of the commands:

grep -i "new backli" /var/log/* dmesg |grep -i "back"

Maybe it does not reach that line of code? Or the log should be visible somewhere else... ?

Can somebody help...?

https://bugzilla.kernel.org/show_bug.cgi?id=203905

Kunal Bhat (kunal.bhat2001@gmail.com) changed:

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--- Comment #9 from Kunal Bhat (kunal.bhat2001@gmail.com) --- (In reply to Flo Bock from comment #8)

With recent systemd changes, the 16 bit values in actual_brightness break saving and restoring the backlight values using AMDGPU. According to a closed issue on Github, Lennart Poettering sees this as a kernel issue[1]. Is there any good reason for actual_brightness to be 16bit, whereas both max_brightness and brightness are 8bit?

I believe it's there to provide a higher range of precision for the backlight. Not sure why they never extended the range for max_brightness.

The systemd devs are adamant that this is a driver issue, and aren't ready to implement a work around for it. I believe this is the open issue with the discussions right now: https://github.com/systemd/systemd/issues/16630

https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #11 from Alexander Monakov (amonakov@gmail.com) --- v2 patch: https://lore.kernel.org/lkml/20200804201313.6464-1-amonakov@ispras.ru/

https://bugzilla.kernel.org/show_bug.cgi?id=203905

shanmukhateja@gmail.com (shanmukhateja@gmail.com) changed:

What |Removed |Added ---------------------------------------------------------------------------- CC| |shanmukhateja@gmail.com

--- Comment #13 from shanmukhateja@gmail.com (shanmukhateja@gmail.com) --- I have built a workaround for this issue by forking systemd-backlight for the time-being. It has been tested on my ASUS TUF FX505DT with Ryzen 3550H.

https://github.com/shanmukhateja/systemd/tree/fix-amdgpu-backlight

https://bugzilla.kernel.org/show_bug.cgi?id=203905

John Shand (jshand2013@gmail.com) changed:

What |Removed |Added ---------------------------------------------------------------------------- CC| |jshand2013@gmail.com

--- Comment #15 from John Shand (jshand2013@gmail.com) --- i have had this problem as well. was recently working well with kernel 5.8.7. i then install ucode-amd and then grub-mkconfig -o /boot/grub/grub.cfg to set the changes. grub automatically made the new code image work with initramfs and then, backlight went back to about 20% or 255.

would this have anything to do with amd's ucode image??

https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #17 from John Shand (jshand2013@gmail.com) --- Created attachment 292419 --> https://bugzilla.kernel.org/attachment.cgi?id=292419&action=edit Journalctl 8-9-2020

https://bugzilla.kernel.org/show_bug.cgi?id=203905

kurmikon@libero.it changed:

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--- Comment #19 from kurmikon@libero.it --- I confirm that the bug is not fixed in 5.9.12.

https://github.com/systemd/systemd/issues/17826

As Poettering pointed out, actual_brightness is read-only and reports the brightness currently in effect, while brightness is writable and reports the value set by userspace.

Not only the actual brightness is in a different range that breaks systemd backlight restoring service at startup, but on my device its value is also fixed on the same value while it should reflect the correct level on brightness changes.

Brightness at the maximum: /sys/class/backlight/amdgpu_bl0/actual_brightness > 249 /sys/class/backlight/amdgpu_bl0/brightness > 255 /sys/class/backlight/amdgpu_bl0/max_brightness > 255

Brightness at the minimum: /sys/class/backlight/amdgpu_bl0/actual_brightness > 249 /sys/class/backlight/amdgpu_bl0/brightness > 2 /sys/class/backlight/amdgpu_bl0/max_brightness > 255

https://bugzilla.kernel.org/show_bug.cgi?id=203905

Paulo Nascimento (paulo.ulusu@googlemail.com) changed:

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--- Comment #21 from Paulo Nascimento (paulo.ulusu@googlemail.com) --- I confirm that the bug is not fixed in kenel 5.11-rc3

max brightness: [pn@pn-legion backlight]$ cat /sys/class/backlight/amdgpu_bl1/actual_brightness 311 [pn@pn-legion backlight]$ cat /sys/class/backlight/amdgpu_bl1/brightness 255 [pn@pn-legion backlight]$ cat /sys/class/backlight/amdgpu_bl1/max_brightness 255

min brightness: [pn@pn-legion backlight]$ cat /sys/class/backlight/amdgpu_bl1/actual_brightness 311 [pn@pn-legion backlight]$ cat /sys/class/backlight/amdgpu_bl1/brightness 0 [pn@pn-legion backlight]$ cat /sys/class/backlight/amdgpu_bl1/max_brightness 255

My laptop has an amd ryzen 5 4600h with renoir igpu and nvidia dgpu. Tests are done with renoir igpu:

[pn@pn-legion backlight]$ inxi -G Graphics: Device-1: NVIDIA TU116M [GeForce GTX 1660 Ti Mobile] driver: nouveau v: kernel Device-2: Advanced Micro Devices [AMD/ATI] Renoir driver: amdgpu v: kernel Device-3: Chicony Integrated Camera type: USB driver: uvcvideo Display: x11 server: X.Org 1.20.10 driver: loaded: amdgpu,ati,modesetting,nouveau resolution: 1920x1080~120Hz OpenGL: renderer: AMD RENOIR (DRM 3.40.0 5.11.0-1-MANJARO LLVM 11.0.1) v: 4.6 Mesa 20.3.3

https://bugzilla.kernel.org/show_bug.cgi?id=203905

m11.1l1.f64@gmail.com changed:

What |Removed |Added ---------------------------------------------------------------------------- CC| |m11.1l1.f64@gmail.com

--- Comment #23 from m11.1l1.f64@gmail.com --- There's a workaround here

I hope it helps :)

simply write this into `/etc/systemd/system/backlight-fix.service`:

``` [Unit] Description=Dummy service for attempting to start the problematic amdgpu_bl0 service

[Service] Type=simple ExecStart=systemctl start systemd-backlight@backlight:amdgpu_bl0

[Install] WantedBy=multi-user.target ```

And then `sudo systemctl enable --now backlight-fix.service`

Bingo!!

The problem is gone

https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #25 from m11.1l1.f64@gmail.com --- I found another workaround and it's easier than EVER and it's done via mkinitcpio😁

First, what's mkinitcpio(https://wiki.archlinux.org/index.php/Mkinitcpio)?

The initial ramdisk is in essence a very small environment (early userspace) which loads various kernel modules and sets up necessary things before handing over control to init. This makes it possible to have, for example, encrypted root file systems and root file systems on a software RAID array. mkinitcpio allows for easy extension with custom hooks, has autodetection at runtime, and many other features.

So go ahead and edit with `sudo nano /etc/mkinitcpio.conf`

Then add the "amdgpu" in the modules section like this:

`MODULES=(amdgpu)`

After that, simply run `sudo mkinitcpio -P` so that it regenerates mkinitcpio for all kernels

This solved my issue, I hope it works for others too :)_

https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #27 from kurmikon@libero.it --- For me the only workaround to avoid this bug is disabling systemd backlight restoration. Then use brillo and enable a specific service to restore the brightness at startup.

https://bugzilla.kernel.org/show_bug.cgi?id=203905

Filip Hejsek (filip.hejsek@gmail.com) changed:

What |Removed |Added ---------------------------------------------------------------------------- CC| |filip.hejsek@gmail.com

--- Comment #29 from Filip Hejsek (filip.hejsek@gmail.com) --- All the workarounds posted here are for a different bug: https://bugzilla.kernel.org/show_bug.cgi?id=210263

There are three different problems: - setting brightness doesn't work before showing something on display (the bug linked above) - actual_brightness has wrong range (this bug) - kernel uses aux for backlight control on systems that don't support it

For the third problem, there is a patch in https://bugzilla.opensuse.org/show_bug.cgi?id=1180749, and it seems to be merged already. However, because there is no way yet to detect that aux backlight doesn't work, the workaround has to be enabled with amdgpu.aux_backlight=0 (assuming you have a kernel with the patch).

https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #31 from Paulo Nascimento (paulo.ulusu@googlemail.com) --- Error messages are: Mai 03 23:01:37 pn-legion systemd-backlight[861]: Failed to get backlight or LED device 'backlight:acpi_video1': No such device Mai 03 23:01:37 pn-legion systemd-backlight[862]: amdgpu_bl1: Failed to write system 'brightness' attribute: No such device or address Mai 03 23:01:37 pn-legion systemd[1]: Failed to start Load/Save Screen Backlight Brightness of backlight:acpi_video1.

I think it has to do with the NVIDIA device.

https://bugzilla.kernel.org/show_bug.cgi?id=203905

--- Comment #33 from Filip Hejsek (filip.hejsek@gmail.com) --- Forgot to mention: since your AMD GPU has number 1 (not 0), you need to replace acpi_video0 with acpi_video1 in my workaround.

(To others: sorry for the email spam)