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[ Upstream commit3cf3b7f012] The apple-gmux driver only binds to old GMUX devices which have an IORESOURCE_IO resource (using inb()/outb()) rather then memory-mapped IO (IORESOURCE_MEM). T2 MacBooks use the new style GMUX devices (with IORESOURCE_MEM access), so these are not supported by the apple-gmux driver. This is not a problem since they have working ACPI video backlight support. But the apple_gmux_present() helper only checks if an ACPI device with the "APP000B" HID is present, causing acpi_video_get_backlight_type() to return acpi_backlight_apple_gmux disabling the acpi_video backlight device. Add a new apple_gmux_backlight_present() helper which checks that the "APP000B" device actually is an old GMUX device with an IORESOURCE_IO resource. This fixes the acpi_video0 backlight no longer registering on T2 MacBooks. Note people are working to add support for the new style GMUX to Linux: https://github.com/kekrby/linux-t2/commits/wip/hybrid-graphics Once this lands this patch should be reverted so that acpi_video_get_backlight_type() also prefers the gmux on new style GMUX MacBooks, but for now this is necessary to avoid regressing backlight control on T2 Macs. Fixes:21245df307("ACPI: video: Add Apple GMUX brightness control detection") Reported-and-tested-by: Aditya Garg <gargaditya08@live.com> Signed-off-by: Hans de Goede <hdegoede@redhat.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Sasha Levin <sashal@kernel.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.