Asus z00l: Backlight doesn't turn on

[Ro-Den]

In my device (ASUS ZenFone 2 Laser ZE550KL aka z00l) back light refuses to turn on at all.

I've managed to turn it on once by
$ echo 50 > /sys/class/backlight/1a98000.dsi.0/brightness
$ echo 250 > /sys/class/backlight/1a98000.dsi.0/brightness

The issue persists on at least 3 user interfaces I've tested: Phosh (Wayland), Sxmo-de-sway (Wayland), Sxmo-de-dwm (X11).

Adding a udev rule as proposed by @Jakko3 in #268 has not resolved the issue.

There are no significant errors in dmesg output:

[    1.601106] msm_mdp 1a01000.display-controller: [drm:adreno_request_fw [msm]] *ERROR* failed to load a300_pm4.fw
[    5.123357] l13: voltage operation not allowed
[   21.692970] msm_mdp 1a01000.display-controller: [drm:adreno_request_fw [msm]] loaded qcom/a300_pm4.fw from new location
[   21.693420] msm_mdp 1a01000.display-controller: [drm:adreno_request_fw [msm]] loaded qcom/a300_pfp.fw from new location

P.S.: Unfortunately, my device is a little bit broken with the Power Button completely ripped off. But I don't think it has something to do with the issue ):

[stephan-gh]

There have been several reports of this issue but so far I have not been able to figure out why this happens. And I don't have this device myself.

It would be helpful if we knew if the display actually ever worked properly (perhaps there is some device-specific difference and it works only on some models like @antony-jr's?). It may help to build e.g. the good old v5.11.7-msm8916 tag again and see if it works there.

So far investigating this issue always failed because the reporters disappeared eventually or where not willing to go through the effort of building the kernel repeatedly to debug this issue. Someone needs to step up if we want to solve this properly.

If you need help with the build process etc please join the chat at #msm8916:postmarketos.org on Matrix since it's easier to help there.

[antony-jr]

My device display and battery is broken, but I've been meaning to repair and try the latest version of the kernel myself. But this is going to take some time to do the repairs. Give me a week or two, but can't promise anything.

[Ro-Den]

It would be helpful if we knew if the display actually ever worked properly

No, it never did in pmOS. There were no problems (except GPS) in Android though my device is not in a good shape ):

perhaps there is some device-specific difference and it works only on some models like @antony-jr's?

As far as I know Asus produced 2 models of ASUS ZenFone 2 Laser ZE550KL: z00lDD (for Southeast Asia: Malaysia, Indonesia etc) and z00lD (for the rest of the world).

My device is z00lD. @antony-jr what's yours?

[antony-jr]

My device is z00lD. @antony-jr what's yours?

Mine is Z00LD too.

Edit: Does TWRP work?

[Ro-Den]

Does TWRP work?

Yes, of course.

lk2nd works, too. Except for fastboot commands.

When my device boots, there's the Asus logo for a couple of seconds, then a grey screen for about a second, then boom - back light goes off. Is it normal behavior? Maybe some over voltage protection steps in?

[vknecht]

Edit : Sorry, meant to post this comment on #268

[Ro-Den]

I have finally tested a number of older kernels.

First, I tried to build the good old v5.11.7-msm8916 myself, but encountered a lot of issues. After that I switched to the relevant branch, added and built my device, but still could not get back light working. Then I tried a number of newer kernels same way, but the issue persisted.

[knuxify]

I don't own this device, but I checked the schematics out of curiosity, and it seems that this phone is most likely using the RT4532 chip for backlight control: manufacturer website, datasheet. Depending on how it's connected to the SoC, it may be possible to drive it separately from the panel driver, which might solve some of the issues.

(relevant excerpt from the ZE550KL schematic; if I should remove it, let me know.)

The site mentions PWM control; I'd start by checking if we can't use pwm-backlight to control the backlight, then move on to figuring out if a separate driver isn't necessary.

[Ro-Den]

The back light issue is solved in kernel 6.6.0

But now $ echo 50 > /sys/class/backlight/1a98000.dsi.0/brightness returns Access denied. And changing brightness level requires pressing the Power button.

[Jakko3]

The pmOS wiki page on LEDs contains some possibilities on the permissions in sysfs. This is mainly useful if you want to change it by command line or by script.

• https://wiki.postmarketos.org/wiki/LEDs#Access_via_sysfs

For backlight, however, actually it shouldn't be needed to handle this by command line or script. The brightness control of the user interface (desktop environment) should be able to manage it. In case you want to change something at boot, an udev rule like mentioned in #268 would work without changing persmissions. I'm not sure what you mean by pressing the power button, though.

[Ro-Den]

Thanks!

$ echo 50 | sudo tee /sys/class/backlight/1a98000.dsi.0/brightness works!

Anyway, I have to press the Power button or xdotool key 122 to turn off the display for the changes to come into effect.

[Jakko3]

Anyway, I have to press the Power button or xdotool key 122 to turn off the display for the changes to come into effect.

Ok, thanks for explaining. That seems to be something driver-specific.