Results of requested backlight testing for 6.1

I have received quite a few test reports in response to my previous blog post. Many thanks to everyone who has run the tests and send me their results!

These tests show that as a result of the current 6.1 changes quite a few laptop models will end up with an empty "/sys/class/backlight", breaking users ability to control their laptop panel's brightness.

I have submitted a patch-set for 6.1 upstream to fix this.

More detailed summary/analysis of the received test reports:

• Known Windows laptop models affected by this:
  
  • Acer Aspire 1640
  • HP Compaq nc6120
  • IBM ThinkPad X40
  • System76 Starling Star1
• Known MacBook models affected by this:
  • Apple MacBook 2.1
  • Apple MacBook 4.1
  • Apple MacBook Pro 7.1
• 30 unaffected models
• The Dell Inspiron N4010 has acpi_video support and acpi_osi_is_win8() returns false, so acpi_video_get_backlight_type() returns acpi_video, but acpi_video fails to register a backlight device due to a _BCM eval error. This model already has a DMI quirk for this, so it is unaffected.
• The following laptop models use vendor backlight control method, while also having a native backlight entry under /sys/class/backlight:
  
  • Asus EeePC 901 (native backlight confirmed to work better then vendor)
  • Dell Latitude D610 (native backlight confirmed to also work)
  • Sony Vaio PCG-FRV3 (native backlight control does not work, BIOS from 2003!)

The fixes for 6.1 restore the behavior where userspace can see multiple entries under "/sys/class/backlight" for a single panel and the kernel leaves figuring out which one actually works up to userspace. This is undesirable and having more then 1 backlight device for a single panel also blocks the new backlight userspace API work which I have planned.

This first round of testing has shown that native works well even on systems so old that they don't have acpi_video backlight control support.

So I have prepared a patch series to try again with 6.2 by making native be preferred over vendor, which should avoid the problems seen with the 6.1 changes before the fixes.

Second request for Linux backlight testing for changes planned for 6.2

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.