On Thu, May 06, 2021 at 05:25:30PM -0500, Bjorn Helgaas wrote:

Make your subject something like this so it matches previous practice:

  arm64: PCI: ...

Got it.

The "::" notation probably comes from C++, but doesn't really apply in
C.  In C, we would say "cfg.parent" or "cfg->parent".

But pci_config_window and cfg->parent are probably too low-level for
the subject anyway.  Seems like it should mention Hyper-V, for
instance.

I'm going to make the title something like:

   arm64: PCI: Support root bridge preparation for Hyper-V PCI

works for you? Also I will add comment inside the function as
explanation.

On Mon, May 03, 2021 at 10:46:34PM +0800, Boqun Feng wrote:

quoted

This is purely a hack, for ARM64 Hyper-V guest, there is no
corresponding ACPI device for the root bridge, so the best we can
provide is an all-zeroed pci_config_window, and in this case make
pcibios_root_bridge_prepare() act as the ACPI device is NULL.

Why is there no ACPI device?  Is this a needless arch dependency?  Or
is this related to using DT instead of ACPI?

For Hyper-V virtual PCI host bridges, neither DT or ACPI is used to
describe them, a hypervisor-specific mechanism (VMBus) is used to
enumerate PCI host bridges. So actually on x86, Hyper-V PCI host
bridge's ACPI companion is set as NULL.

The cover letter hints that this might be related to
PCI_DOMAINS_GENERIC=y, but that doesn't sound like a very convincing
reason (and the cover letter can provide an overview, but the commit
logs of individual patches shouldn't assume knowledge of the cover
letter).

Ok, I will add a better explanation in the commit log in the next
version. Thanks!

Regards,
Boqun

quoted

Signed-off-by: Boqun Feng <redacted>
---
 arch/arm64/kernel/pci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
index e9a6eeb6a694..f159df903ccb 100644
--- a/arch/arm64/kernel/pci.c
+++ b/arch/arm64/kernel/pci.c

@@ -83,7 +83,7 @@ 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);
+		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