Second request for Linux backlight testing for changes planned for 6.2

[hansdegoede]

As mentioned in my previous blog post, I have written a new patch series for 6.2 to try to avoid having multiple entries in /sys/class/backlight for a single panel again.

This new series might cause regressions on a different set of even older laptop models then the one affected by the 6.1 backlight work. So I'm again looking for people willing to run a few quick tests.

To see if your laptop is possibly affected by the 6.2 change please run:

• ls /sys/class/backlight

if the output of this command contains both:

1. A GPU native backlight device, with intel/nv/nvidia/amd/radeon/psb/oaktrail in the name; and
2. A vendor backlight device, with either a model-series: eeepc, ideapad, thinkpad, etc; or a vendor-name: acer, asus, dell, toshiba, sony, etc. in the name

then 6.2 will cause a behavior change on your device, it will hide the vendor backlight device in preference of the native backlight device.

If your laptop shows only a native or only a vendor backlight device (possibly in combination with another type of backlight device such as acpi_video#), then your laptop will not be affected by the planned changes for 6.2.

Note that I expect only very old models to be affected, e.g. the Sony Vaio PCG-FRV3
from 2003 is known to be affected.

If your laptop has both native + vendor backlight devices, then please do 2 things:

1. Please run the following commands:
   1. ls /sys/class/backlight > ls-backlight.txt
   2. sudo dmesg > dmesg.txt
   3. sudo dmidecode > dmidecode.txt
   4. sudo acpidump -o acpidump.txt
2. Please test if the native backlight interface works, the example below assumes the native backlight is called "intel_backlight":
   1. cd /sys/class/backlight/intel_backlight
   2. cat max_brightness
   3. <the "cat max_brightness" will show the maximum brightness value supported>
   4. echo $max_brightness_value > brightness
   5. echo $half-of-max_brightness_value > brightness

 

Where if for example cat max_brightness returns 255 then $max_brightness_value
is 255 and $half-of-max_brightness_value is 127. And then check if the brightness of the backlight actually changes when you do this ?

After generating the 4 .txt files and running the native backlight tests, please send me an email about this at hdegoede@redhat.com with the results of the native backlight tests (panel brightness changes when echo-ing values to brightness or not?) and with the 4 generated .txt files attached.

If the native backlight interface works then things should keep working fine with 6.2 and typically you will get more fine-grained brightness control as an added bonus. Please send me an email with the test results even if the native backlight interface works.