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commitf64e4275efupstream. The Dell Latitude E6430 both with and without the optional NVidia dGPU has a bug in its ACPI tables which is causing Linux to assign the wrong ACPI fwnode / companion to the pci_device for the i915 iGPU. Specifically under the PCI root bridge there are these 2 ACPI Device()s : Scope (_SB.PCI0) { Device (GFX0) { Name (_ADR, 0x00020000) // _ADR: Address } ... Device (VID) { Name (_ADR, 0x00020000) // _ADR: Address ... Method (_DOS, 1, NotSerialized) // _DOS: Disable Output Switching { VDP8 = Arg0 VDP1 (One, VDP8) } Method (_DOD, 0, NotSerialized) // _DOD: Display Output Devices { ... } ... } } The non-functional GFX0 ACPI device is a problem, because this gets returned as ACPI companion-device by acpi_find_child_device() for the iGPU. This is a long standing problem and the i915 driver does use the ACPI companion for some things, but works fine without it. However since commit63f534b8ba("ACPI: PCI: Rework acpi_get_pci_dev()") acpi_get_pci_dev() relies on the physical-node pointer in the acpi_device and that is set on the wrong acpi_device because of the wrong acpi_find_child_device() return. This breaks the ACPI video code, leading to non working backlight control in some cases. Add a type.backlight flag, mark ACPI video bus devices with this and make find_child_checks() return a higher score for children with this flag set, so that it picks the right companion-device. Fixes:63f534b8ba("ACPI: PCI: Rework acpi_get_pci_dev()") Co-developed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Hans de Goede <hdegoede@redhat.com> Cc: 6.1+ <stable@vger.kernel.org> # 6.1+ 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.