Re: [Regression] Bug 217026 - Backlight control broken on kernels 6.1.4+

["Linux regression tracking (Thorsten Leemhuis)" <regressions@leemhuis.info>]

On 14.02.23 15:59, Hans de Goede wrote:
> 
> On 2/14/23 11:44, Linux regression tracking (Thorsten Leemhuis) wrote:
>> Hi, this is your Linux kernel regression tracker.
>>
>> I noticed a regression report in bugzilla.kernel.org. As many (most?)
>> kernel developer don't keep an eye on it, I decided to forward it by
>> mail. Quoting from https://bugzilla.kernel.org/show_bug.cgi?id=217026 :
>>
>>>  albimarini4283@gmail.com 2023-02-12 20:57:03 UTC
>>>
>>> Brightness control does not work with AMD Ryzen 5800H when using hybrid
>>> graphics on kernel updates 6.1.4+. I am using a Lenovo Legion Slim 7
>>> (2021, 15ACH6) currently running Arch Linux with the mainline kernel
>>> 6.1.11, however, I have been testing my experience with this issue on
>>> every point revision from 6.1.3 to 6.1.11.
>>>
>>>       CPU: AMD Ryzen 5 5800H with Radeon Graphics
>>>       GPU: NVIDIA RTX 3060 Mobile / Max-Q (Proprietary NVIDIA driver,
>>> tested with 525.78.01-1 (version prior to 6.1.4 being released) and
>>> 525.89.02-1 (latest driver at time of writing))
>>>       System Memory: 40 GB
>>>       Display: Laptop (Laptop Screen)
>>>
>>> The only parameters applied at boot on my system are: nvidia-drm.modeset=1
>>>
>>> How to reproduce the issue:
>>> Enable hybrid graphics/Optimus in BIOS setup.
>>>
>>> Prior to kernel version 6.1.4, /sys/class/backlight contained two entries:
>>> amdgpu_bl0 and nvidia_wmi_ec_backlight
>>>
>>> With these two entries in /sys/class/backlight , I was able to write to
>>> their respective brightness files directly or use a program like light
>>> to change the values. Those values would change the brightness of the
>>> screen depending on if I was using the AMD GPU or NVIDIA GPU to display
>>> the current application. I could set these values to roughly the same
>>> thing to achieve an overall complete brightness experience regardless of
>>> whether or not I was currently running an application on my integrated
>>> (AMD) GPU or dedicated (NVIDIA) GPU.
>>>
>>> Then, upon updating to kernel versions 6.1.4+, there is no longer an
>>> amdgpu_bl0 entry in /sys/class/backlight , just a
>>> nvidia_wmi_ec_backlight entry, making it impossible for me to change the
>>> brightness on my display when using the iGPU. Interestingly, on kernels
>>> 6.1.4+, running "journalctl -b -0 | grep backlight" returns an output
>>> "amdgpu: [drm] Skipping amdgpu DM backlight registration", which was not
>>> present in prior kernel versions.
>>>
>>> However, if I instead prepend the option "acpi_backlight=native" to my
>>> kernel command line options at boot, "amdgpu_bl0" is once again present
>>> in /sys/class/backlight but "nvidia_wmi_ec_backlight" has now
>>> disappeared and is nowhere to be seen making it so I can change the
>>> brightness when using the iGPU, but the brightness is stuck at max when
>>> using the dedicated GPU. Running the above journalctl command at this
>>> point returns no errors relating to my AMD GPU and does not mention
>>> anything about the NVIDIA GPU. Trying different acpi_backlight options
>>> on 6.1.4+ does not fix the issue and instead removes functionality.
>>> acpi_backlight=vendor makes an entry called "ideapad" pop up in
>>> /sys/class/backlight with nothing else. Changing the brightness values
>>> in ideapad does nothing.
>>> acpi_backlight=video makes only two entries appear in
>>> /sys/class/backlight, acpi_video0 and acpi_video1. Changing the
>>> brightness values in either of these directories does nothing.
>>> acpi_backlight=none causes nothing to appear under /sys/class/backlight.
>>>
>>> If hybrid graphics is disabled, the display is connected to the NVIDIA
>>> GPU and /sys/class/backlight/nvidia_0 is present, the NVIDIA driver can
>>> change the display brightness without a problem.p
>>>
>>> Below is my lscpi -nn and dmidecode outputs on kernel 6.1.3 and 6.1.11.
>>> [...]
>>
>> See the ticket for more details.
>>
>> [TLDR for the rest of this mail: I'm adding this report to the list of
>> tracked Linux kernel regressions; the text you find below is based on a
>> few templates paragraphs you might have encountered already in similar
>> form.]
>>
>> BTW, let me use this mail to also add the report to the list of tracked
>> regressions to ensure it's doesn't fall through the cracks:
>>
>> #regzbot introduced: v6.1.3..v6.1.4
>> https://bugzilla.kernel.org/show_bug.cgi?id=217026
>> #regzbot title: backlight: brightness control stopped working on a Ryzen
>> system with hybrid graphics
>> #regzbot ignore-activity
> 
> Thank you for forwarding this.

yw

> I have just added the following comment to the bug:
> [...]
> Lets continue this inside bugzilla.

Thx. FWIW, at least from my side there is no need to post replies to
bugzilla and the list; some developers prefer one, some the other -- and
regzbot will notice replies to both places.

It's IMHO unfortunate that we have to deal with two places, but well,
that's how it is.

Ciao, Thorsten

P.S.: while at it, let me tell regzbot that this one will take some time
to get resolved:

#regzbot backburner: known bios issue, that why there where tricky
aspects beforehand as well; someone from Nvidia is looking into this