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commita5b2781dcaupstream. The Lenovo ThinkPad W530 uses a nvidia k1000m GPU. When this gets used together with one of the older nvidia binary driver series (the latest series does not support it), then backlight control does not work. This is caused by commit3dbc80a3e4("ACPI: video: Make backlight class device registration a separate step (v2)") combined with commit5aa9d943e9("ACPI: video: Don't enable fallback path for creating ACPI backlight by default"). After these changes the acpi_video# backlight device is only registered when requested by a GPU driver calling acpi_video_register_backlight() which the nvidia binary driver does not do. I realize that using the nvidia binary driver is not a supported use-case and users can workaround this by adding acpi_backlight=video on the kernel commandline, but the ThinkPad W530 is a popular model under Linux users, so it seems worthwhile to add a quirk for this. I will also email Nvidia asking them to make the driver call acpi_video_register_backlight() when an internal LCD panel is detected. So maybe the next maintenance release of the drivers will fix this... Fixes:5aa9d943e9("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.