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panel_power_savings resets brightness to max after sleep with screen off

Brief summary of the problem:

Turning off the display (by setting the CRTC ACTIVE property to 0 through KMS), suspending (S3) while the screen is off, then enabling panel_power_savings causes the display backlight to reset to max brightness. If panel_power_savings was enabled before suspend, then brightness is reset to max immediately after resume.

This causes brightness to be reset to max after resuming from suspend in GNOME, because gnome-settings-daemon turns off the display before suspending.

Hardware description:

Lenovo ThinkPad E15 Gen 2

  • CPU: AMD Ryzen 7 4700U with Radeon Graphics
  • GPU: 04:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Renoir [Radeon Vega Series / Radeon Vega Mobile Series] [1002:1636] (rev c2)
  • System Memory: 16GB DDR4 3200 MHz
  • Display(s): Laptop screen 1920x1080
  • Type of Display Connection: eDP

System information:

  • Distro name and Version: Arch Linux
  • Kernel version: Linux filip-e15 6.9.7-arch1-1 #1 SMP PREEMPT_DYNAMIC Fri, 28 Jun 2024 04:32:50 +0000 x86_64 GNU/Linux
  • Custom kernel: N/A
  • AMD official driver version: N/A

How to reproduce the issue:

  1. Download the attached test program: bug.c
  2. Compile with gcc $(pkg-config --cflags --libs libdrm) bug.c -o bug
  3. Run the following commands as root from the Linux VT console (either Case 1 or Case 2)

Case 1 (panel_power_savings enabled after suspend):

# disable panel_power_savings
echo 0 >/sys/class/drm/card1-eDP-1/amdgpu/panel_power_savings

# run test program
./bug

# at this point, brightness is still at its original value

# enable panel_power_savings
echo 1 >/sys/class/drm/card1-eDP-1/amdgpu/panel_power_savings

# brightness is now reset to max

Case 2 (panel_power_savings enabled before suspend):

# enable panel_power_savings
echo 1 >/sys/class/drm/card1-eDP-1/amdgpu/panel_power_savings

# run test program
./bug

# brightness is now reset to max

What bug.c does:

First the ACTIVE property of all CRTCs is set to 0, then rtcwake -m mem -s 1 is executed, and then the ACTIVE property is restored to original value.

Attached files:

Test program: bug.c

Additional information

If the brightness is manually changed after running the test program but before enabling panel_power_savings, it will not be reset to max.

The change to max brightness is reflected in the sysfs backlight actual_brightness attribute, but not in the brightness attribute.

This issue is similar to #3086, but there are two key differences:

  1. this issue only occurs when the system is suspended (to S3) while the display is off
  2. this issue occurs only if panel_power_savings is used, which wasn't even supported by the kernel version in #3086
Edited by Filip Hejsek