Nouveau - Apr 2019 - [Bug 110407] New: /sys/class/backlight/nv_backlight doesn't work on Dell Precision 7530 GP107GLM [Quadro P1000 Mobile]

https://bugs.freedesktop.org/show_bug.cgi?id=110407

            Bug ID: 110407
           Summary: /sys/class/backlight/nv_backlight doesn't work on Dell
                    Precision 7530 GP107GLM [Quadro P1000 Mobile]
           Product: xorg
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/nouveau
          Assignee: nouveau at lists.freedesktop.org
          Reporter: kai.heng.feng at canonical.com
        QA Contact: xorg-team at lists.x.org

This laptop has an BIOS option "Switchable Graphics". When the options
is
selected, it behaves like a normal Optimus laptop. In this case, brightness
sysfs works since it's driven by Intel graphics.

When the options is deselected, the Intel graphics device disappears, Nvidia is
the only graphics device. The issue happens in this case.

Changing /sys/class/backlight/nv_backlight/brightness, the brightness level
remains the same - almost no backlight.

Using proprietary driver, brightness gets changed correctly by
/sys/class/backlight/nvidia_0/brightness.

No trace while using MMIOTRACE, under proprietary driver.

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--- Comment #1 from Ilia Mirkin <imirkin at alum.mit.edu> ---
When in non-switchable mode, are there other things in /sys/class/backlight?
e.g. acpi_video0?

Also, presumably this is on v5.0 or later? Prior to that, there was no
backlight support for Pascal.

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--- Comment #2 from Kai-Heng Feng <kai.heng.feng at canonical.com> ---
(In reply to Ilia Mirkin from comment #1)
> When in non-switchable mode, are there other things in
/sys/class/backlight?
> e.g. acpi_video0?
No, nv_backlight (or nvidia_0) is the only interface.

I also tried to call _BCM directly via acpidbg, but both Intel's and
Nvidia's
_BCM method changes nothing.

Please refer to the original bug report [1].
> 
> Also, presumably this is on v5.0 or later? Prior to that, there was no
> backlight support for Pascal.
Yes, on both v5.0 and linux-next.

[1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1821882

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--- Comment #3 from Kai-Heng Feng <kai.heng.feng at canonical.com> ---
Any further ideas that I can try?

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Martin Peres <martin.peres at free.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |MOVED

--- Comment #4 from Martin Peres <martin.peres at free.fr> ---
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