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ATM on x86 laptops where we want userspace to use the acpi_video backlight device we often register both the GPU's native backlight device and acpi_video's firmware acpi_video# backlight device. This relies on userspace preferring firmware type backlight devices over native ones, but registering 2 backlight devices for a single display really is undesirable. On x86 laptops where the native GPU backlight device should be used, the registering of other backlight devices is avoided by their drivers using acpi_video_get_backlight_type() and only registering their backlight if the return value matches their type. acpi_video_get_backlight_type() uses backlight_device_get_by_type(BACKLIGHT_RAW) to determine if a native driver is available and will never return native if this returns false. This means that the GPU's native backlight registering code cannot just call acpi_video_get_backlight_type() to determine if it should register its backlight, since acpi_video_get_backlight_type() will never return native until the native backlight has already registered. To fix this add a new internal native function parameter to acpi_video_get_backlight_type(), which when set to true will make acpi_video_get_backlight_type() behave as if a native backlight has already been registered. And add a new acpi_video_backlight_use_native() helper, which sets this to true, for use in native GPU backlight code. Changes in v2: - Replace adding a native parameter to acpi_video_get_backlight_type() with adding a new acpi_video_backlight_use_native() helper. Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
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.