[Bug 208661] New: Backlight doesn't work with both nv_backlight and acpi_video

[Bug 208661] New: Backlight doesn't work with both nv_backlight and acpi_video

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=208661

            Bug ID: 208661
           Summary: Backlight doesn't work with both nv_backlight and
                    acpi_video
           Product: Drivers
           Version: 2.5
    Kernel Version: 5.7.0-1-amd64
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri@kernel-bugs.osdl.org
          Reporter: iknstudio@protonmail.com
        Regression: No

Created attachment 290457
  --> https://bugzilla.kernel.org/attachment.cgi?id=290457&action=edit
vbios.rom

Hi,

I'm trying to get backlight working on this laptop. I am using the nouveau
driver, and kernel 5.7.
I tried a few different parameters for acpi_osi=, like the following:
 - acpi_osi=linux
 - acpi_osi=! acpi_osi="Windows 2012"
 - acpi_osi=! acpi_osi="Windows 2015"
however, none of them worked. /sys/class/backlight/*/bl_power is 0 for both
devices at boot. acpi_video0 has a max_brightness of 10 while nv_backlight has
a max brightness of 100.

I am attaching the vbios. The graphics card is nVidia GT540M.

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[Bug 208661] Backlight doesn't work with both nv_backlight and acpi_video

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=208661

--- Comment #1 from Shannon Gaines (iknstudio@protonmail.com) ---
Created attachment 290477
  --> https://bugzilla.kernel.org/attachment.cgi?id=290477&action=edit
acpidump.txt

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[Bug 208661] Backlight doesn't work with both nv_backlight and acpi_video

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=208661

--- Comment #2 from Shannon Gaines (iknstudio@protonmail.com) ---
Update: nvidia-legacy-390xx driver allows me to change the backlight via
acpi_video0, however nouveau doesn't under any circumstances. No clue why.

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[Bug 208661] Backlight doesn't work with both nv_backlight and acpi_video

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=208661

Ilia Mirkin (imirkin@alum.mit.edu) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |imirkin@alum.mit.edu

--- Comment #3 from Ilia Mirkin (imirkin@alum.mit.edu) ---
So given that this works via acpi_video with NVIDIA's drivers, this suggests to
me that nouveau is either doing something it shouldn't, which breaks the acpi
method, or it doesn't do something which enables the acpi method to work.

Unfortunately I'm not an expert on the ACPI stuff, so we need to

1. Figure out how acpi_video works (BCL method? something like that)
2. Find the method in the acpi dump, and decode it
3. Profit...

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[Bug 208661] Backlight doesn't work with both nv_backlight and acpi_video

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=208661

--- Comment #4 from Shannon Gaines (iknstudio@protonmail.com) ---
As suggested in IRC, I tried nouveau.modeset=0. It didn't help with the
backlight issue, without or without non-free firmware. So I believe the issue
isn't related to modesetting.

To be clear, I tested:
 - nouveau + modeset=0 + no firmware
 - nouveau + no firmware
 - nouveau + modeset=0 + firmware
 - nouveau + firmware

And nothing helped.

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[Bug 208661] Backlight doesn't work with both nv_backlight and acpi_video

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=208661

--- Comment #5 from Shannon Gaines (iknstudio@protonmail.com) ---
Created attachment 290549
  --> https://bugzilla.kernel.org/attachment.cgi?id=290549&action=edit
mmiotrace for nvidia initialization

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[Bug 208661] Backlight doesn't work with both nv_backlight and acpi_video

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=208661

--- Comment #6 from Ilia Mirkin (imirkin@alum.mit.edu) ---
After a lot of debugging on IRC, here are a few facts that are worth recording:

1. The nv_backlight "method" works -- i.e. the backlight is hooked up to the
GPU. Adjusting brightness via acpi_video connects to the same mechanism
somehow. We didn't dig too deep to figure out how, since it's not really
important.

2. At the start of the mmiotrace, the NVIDIA driver fixes up 0xe100
("PNVIO.GPIO_MODE_0") to be have the 0x4 bit set of the SOR mask. On bootup
it's 0x00180100, while it should be 0x001c0100.

3. This is equivalent to what we do in nv50_gpio_reset. This function is called
in response to the "GPIO" init table method (which, one might mention, is
present in the init tables).

4. Manually setting this value (via nvapoke) makes nv_backlight work. Doing
suspend/resume, which causes init tables to be re-run, makes nv_backlight also
work, since the init table contains the GPIO opcode.

5. Regular boot with NvForcePost=1 kills the panel (and maybe other things).

Not sure what the solution is. Right now we run nv50_gpio_reset unconditionally
on MBP10,1. We can start extending the DMI table with random laptops, or maybe
we can just run that function unconditionally. Is there a downside?

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[Bug 208661] Backlight doesn't work with both nv_backlight and acpi_video

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=208661

--- Comment #7 from Shannon Gaines (iknstudio@protonmail.com) ---
Created attachment 290619
  --> https://bugzilla.kernel.org/attachment.cgi?id=290619&action=edit
Patch to add NvForceGpioReset config option

I created a patch that allows users to force a GPIO reset everytime the GPU is
initialized as a work-around for this bug. I've attached it.

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