7d40c0f70d
Currently at root bridge preparation, the corresponding ACPI device will be set as the companion, however for a Hyper-V virtual PCI root bridge, there is no corresponding ACPI device, because a Hyper-V virtual PCI root bridge is discovered via VMBus rather than ACPI table. In order to support this, we need to make pcibios_root_bridge_prepare() work with cfg->parent being NULL. Use a NULL pointer as the ACPI device if there is no corresponding ACPI device, and this is fine because: 1) ACPI_COMPANION_SET() can work with the second parameter being NULL, 2) semantically, if a NULL pointer is set via ACPI_COMPANION_SET(), ACPI_COMPANION() (the read API for this field) will return NULL, and since ACPI_COMPANION() may return NULL, so users must have handled the cases where it returns NULL, and 3) since there is no corresponding ACPI device, it would be wrong to use any other value here. Link: https://lore.kernel.org/r/20210726180657.142727-5-boqun.feng@gmail.com Signed-off-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> Acked-by: Catalin Marinas <catalin.marinas@arm.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.