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.
Hans de Goede
authored
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 commit 63f534b8 ("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: 63f534b8 ("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>