On Tue, Jul 27, 2021 at 02:06:53AM +0800, Boqun Feng wrote: > 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. > > Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx> Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
