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There have been 2 separate reports now about a non working "dell_backlight" device getting registered under /sys/class/backlight 1 report for a Raptor Lake based Dell and 1 report for a Meteor Lake (development) platform. On hw from the last 10 years dell-laptop will not register "dell_backlight" because acpi_video_get_backlight_type() will return acpi_backlight_video there if called before the GPU/kms driver loads. So it does not matter if the GPU driver's native backlight is registered after dell-laptop loads. But it seems that on the latest generation laptops the ACPI tables no longer contain acpi_video backlight control support which causes acpi_video_get_backlight_type() to return acpi_backlight_vendor causing "dell_backlight" to get registered if the dell-laptop module is loaded before the GPU/kms driver. Vendor specific backlight control like the "dell_backlight" device is only necessary on quite old hw (from before acpi_video backlight control was introduced). Work around "dell_backlight" registering on very new hw (where acpi_video backlight control seems to be no more) by making acpi_video_get_backlight_type() return acpi_backlight_none instead of acpi_backlight_vendor as final fallback when the ACPI tables have support for Windows 8 or later (laptops from after ~2012). Suggested-by: Matthew Garrett <mjg59@srcf.ucam.org> Reported-by: AceLan Kao <acelan.kao@canonical.com> Closes: https://lore.kernel.org/platform-driver-x86/20230607034331.576623-1-acelan.kao@canonical.com/ Signed-off-by: Hans de Goede <hdegoede@redhat.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.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.