[RFC v4 3/7] arm64: PCI: Support root bridge preparation for Hyper-V PCI

[Boqun Feng]

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.

Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
---
 arch/arm64/kernel/pci.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
index 1006ed2d7c60..3b81ac42bc1f 100644
--- a/arch/arm64/kernel/pci.c
+++ b/arch/arm64/kernel/pci.c
@@ -84,7 +84,13 @@ int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
 {
 	if (!acpi_disabled) {
 		struct pci_config_window *cfg = bridge->bus->sysdata;
-		struct acpi_device *adev = to_acpi_device(cfg->parent);
+		/*
+		 * On Hyper-V there is no corresponding APCI device for a root
+		 * bridge, therefore ->parent is set as NULL by the driver. And
+		 * set 'adev` as NULL in this case because there is no proper
+		 * ACPI device.
+		 */
+		struct acpi_device *adev = cfg->parent ? to_acpi_device(cfg->parent) : NULL;
 		struct device *bus_dev = &bridge->bus->dev;
 
 		ACPI_COMPANION_SET(&bridge->dev, adev);
-- 
2.30.2