Precision 7730 -- brightness adjustment stops working in latest BIOS

I have a Dell Precision 7530, without the option to enable or disable GPU switching and just have an internal GPU. I've been experiencing the same problem and have managed to fix it by modifying the DSDT (which I would not recommend to others) and removing "External (_SB_.PCI0.PEG0.NHDA, UnknownObj)" and "External (NHDA, UnknownObj)" and anything trying to read or write those. Please don't use deflection techniques on people by saying it's not a HW issue if it works in BIOS as this is a software issues in ACPI, and while you may or may not be using DSDT in the Setup, OS will and need a clear documentation or specification on what NHDA is.

The reason backlight switching worked in BIOS version 1.10.1 was that the keypresses were passed to the OS instead of being handled in ACPI, and now it's different. Please try to be more succint in the changelogs on what's happening, rather than "Fix backlight...", which you haven't. The reason we buy Dell HW is because of its quality and compliance to standards which usually lead to great Linux support. I hope this will help you to escalate to managers on what's important...

WOW, that's some great sleuthing, @delta78561 .  I can't believe you modified the ACPI's DSDT.  You've been able to present the issue that we've all been saying, but couldn't prove.  Now we know why it affects multiple OS's but not the EFI.  Keypresses have been going to ACPI since 1.10.1 BIOS, instead of passed to the kernel.  Thanks! 

Now it's Dell's turn to work with the community and provide documentation of the ACPI methods, it seems.

I wrote another comment a few times, adding was confirmed, then whole post disappeared - strange, I'll try to add again, smaller parts

About second problem (laptop freezes after resume on battery supply): I tried latest intel-microcode and kernel versions (which are 3.20200616.1 and 5.7.0-1-amd64), additionally installed all missing firmwares, ex.:
W: Possible missing firmware /lib/firmware/i915/cml_huc_4.0.0.bin for module i915
but Dell 7730 still freezes. It is probably another BIOS change after version 1.10.1, so system updates won't resolve the problem.

Is this thread still monitored?  I wanted to mention I have exactly the same issue.  Whether trying to adjust brightness with Windows Settings slider or with FN keys, the values change (display brightness status bar in top left corner changes position, but actual screen brightness output does not change).  BIOS looks like vers 1.10.2 date 7/7/2020.

Doubtful, as 7750 is already there. I changed shortcuts for brightness controls to Win+Up and Win+Down, instead of Fn+Up|Down - it works in Linux Debian, Gnome. Maybe similar "workaround" is available in Windows to omit this bug?

Did anyone try 1.14 yet? Are we stuck forever?

Yep, we are, as described above. I installed latest version of firmware:

root@P7730:~# fwupdmgr get-devices
─System Firmware:
│ Identyfikator urządzenia:f6d8adf7724cb115dbb7e99b52f70ddbe1168be0
│ Obecna wersja: 1.14.4
│ Minimalna wersja: 1.14.4
│ Dostawca: Dell Inc. (DMI:Dell Inc.)
│ GUID: db72c932-b3c6-4640-b382-3f4619ab447b

root@P7730:~# fwupdmgr get-updates
Urządzenia bez dostępnych aktualizacji oprogramowania sprzętowego:
• ST8000DM004-2CX188
• UEFI dbx
Urządzenia z najnowszą dostępną wersją oprogramowania sprzętowego:
• Micron 2200 NVMe 256GB
• System Firmware
No updates available for remaining devices

Hi,

Prajwal here from Dell community.

I'm following up with you to check if you are available.

Please get back to us at your convenience so that we can further assist you.

Regards,

Prajwal

Hello,

I'm not sure what assistance are you talking about, Prajwal? As delta78561 user explained, brightness control ceased to work, because you've made changes to DSDT table in BIOS version 1.11 that prevented passing keypresses to operating system. More details you'll find in his message (posted in this thread at 07-11-2020 06:58 AM). He managed to fix it by modifying the DSDT - most users didn't heard about DSDT tables, not even mentioning fixing it on their own.

If you are talking about fixing DSDT table for users less technically advanced than delta78561, then such assistance would be most welcome.

I can tell DELL Cares!

Hi,

Prajwal here from Dell community.

I'm following up with you to check if you are available.

Please get back to us at your convenience so that we can further assist you.

Regards,

Prajwal

Any update on the permanent fix of the subject issue?