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

[Rafael J. Wysocki]

On Thu, Dec 15, 2022 at 8:38 PM Rafael J. Wysocki <rafael at kernel.org> wrote:
>
> 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.

Done now, thanks!