[PATCH v3 0/3] Adjust ACPI video detection fallback path

[Rafael J. Wysocki]

On Thu, Dec 15, 2022 at 8:20 PM Limonciello, Mario
<Mario.Limonciello at amd.com> wrote:
>
> [Public]
>
> > -----Original Message-----
> > From: Limonciello, Mario <Mario.Limonciello at amd.com>
> > Sent: Thursday, December 8, 2022 10:42
> > To: Rafael J . Wysocki <rafael at kernel.org>; Deucher, Alexander
> > <Alexander.Deucher at amd.com>; Hans de Goede
> > <hdegoede at redhat.com>
> > Cc: amd-gfx at lists.freedesktop.org; linux-acpi at vger.kernel.org; Daniel
> > Dadap <ddadap at nvidia.com>; Limonciello, Mario
> > <Mario.Limonciello at amd.com>
> > Subject: [PATCH v3 0/3] Adjust ACPI video detection fallback path
> >
> > In kernel 6.1 the backlight registration code was overhauled so that
> > at most one backlight device got registered. As part of this change
> > there was code added to still allow making an acpi_video0 device if the
> > BIOS contained backlight control methods but no native or vendor drivers
> > registered.
> >
> > Even after the overhaul this fallback logic is failing on the BIOS from
> > a number of motherboard manufacturers supporting Ryzen APUs.
> > What happens is the amdgpu driver finishes registration and as expected
> > doesn't create a backlight control device since no eDP panels are connected
> > to a desktop.
> >
> > Then 8 seconds later the ACPI video detection code creates an
> > acpi_video0 device that is non-operational. GNOME then creates a
> > backlight slider.
> >
> > To avoid this situation from happening make two sets of changes:
> >
> > Prevent desktop problems w/ fallback logic
> > ------------------------------------------
> > 1) Add support for the video detect code to let native drivers cancel the
> > fallback logic if they didn't find a panel.
> >
> > This is done this way so that if another driver decides that the ACPI
> > mechanism is still needed it can instead directly call the registration
> > function.
> >
> > 2) Add code to amdgpu to notify the ACPI video detection code that no panel
> > was detected on an APU.
> >
> > Disable fallback logic by default
> > ---------------------------------
> > This fallback logic was introduced to prevent regressions in the backlight
> > overhaul.  As it has been deemed unnecessary by Hans explicitly disable the
> > timeout.  If this turns out to be mistake and this part is reverted, the
> > other patches for preventing desktop problems will avoid regressions on
> > desktops.
> >
> > Mario Limonciello (3):
> >   ACPI: video: Allow GPU drivers to report no panels
> >   drm/amd/display: Report to ACPI video if no panels were found
> >   ACPI: video: Don't enable fallback path for creating ACPI backlight by
> >     default
> >
> >  drivers/acpi/acpi_video.c                       | 17 ++++++++++++-----
> >  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c   |  4 ++++
> >  include/acpi/video.h                            |  2 ++
> >  3 files changed, 18 insertions(+), 5 deletions(-)
> >
> > --
> > 2.34.1
>
> FYI, besides me, this series also tested successfully by one of the
> reporters to the Red Hat bugzilla.
>
> https://bugzilla.redhat.com/show_bug.cgi?id=1783786#c8

Thanks for letting me know!

I'll queue it up for 6.2-rc next week.