9610adf8b2
commit e506731c8f35699d746c615164ed620cd53c00ca upstream.
Commit 3dbc80a3e4c5 ("ACPI: video: Make backlight class device
registration a separate step (v2)") combined with
commit 5aa9d943e9b6 ("ACPI: video: Don't enable fallback path for
creating ACPI backlight by default")
Means that the video.ko code now fully depends on the GPU driver calling
acpi_video_register_backlight() for the acpi_video# backlight class
devices to get registered.
This means that if the GPU driver does not do this, acpi_backlight=video
on the cmdline, or DMI quirks for selecting acpi_video# will not work.
This is a problem on for example Apple iMac14,1 all-in-ones where
the monitor's LCD panel shows up as a regular DP connection instead of
eDP so the GPU driver will not call acpi_video_register_backlight() [1].
Fix this by making video.ko directly register the acpi_video# devices
when these have been explicitly requested either on the cmdline or
through DMI quirks (rather then auto-detection being used).
[1] GPU drivers only call acpi_video_register_backlight() when an internal
panel is detected, to avoid non working acpi_video# devices getting
registered on desktops which unfortunately is a real issue.
Fixes: 5aa9d943e9b6 ("ACPI: video: Don't enable fallback path for creating ACPI backlight by default")
Cc: All applicable <stable@vger.kernel.org>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.