Re: [RFC 1/2] arm64: PCI: Allow use arch-specific pci sysdata

On Fri, Mar 19, 2021 at 10:14 PM Bjorn Helgaas [off-list ref] wrote:

quoted

However, for a virtualized PCI bus, there might be no enough data in of
or acpi table to create a pci_config_window. This is similar to the case
where CONFIG_PCI_DOMAINS_GENERIC=n, IOW, architectures use their own
structure for sysdata, so no apci table lookup is required.

In order to enable Hyper-V's virtual PCI (which doesn't have acpi table
entry for PCI) on ARM64 (which selects CONFIG_PCI_DOMAINS_GENERIC), we
introduce arch-specific pci sysdata (similar to the one for x86) for
ARM64, and allow the core PCI code to detect the type of sysdata at the
runtime. The latter is achieved by adding a pci_ops::use_arch_sysdata
field.

Originally-by: Sunil Muthuswamy [off-list ref]
Signed-off-by: Boqun Feng (Microsoft) <redacted>
---
 arch/arm64/include/asm/pci.h | 29 +++++++++++++++++++++++++++++
 arch/arm64/kernel/pci.c      | 15 ++++++++++++---
 include/linux/pci.h          |  3 +++
 3 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/pci.h b/arch/arm64/include/asm/pci.h
index b33ca260e3c9..dade061a0658 100644
--- a/arch/arm64/include/asm/pci.h
+++ b/arch/arm64/include/asm/pci.h

@@ -22,6 +22,16 @@

 extern int isa_dma_bridge_buggy;

+struct pci_sysdata {
+     int domain;     /* PCI domain */
+     int node;       /* NUMA Node */
+#ifdef CONFIG_ACPI
+     struct acpi_device *companion;  /* ACPI companion device */
+#endif
+#ifdef CONFIG_PCI_MSI_IRQ_DOMAIN
+     void *fwnode;                   /* IRQ domain for MSI assignment */
+#endif
+};

Our PCI domain code is really a mess (mostly my fault) and I hate to
make it even more complicated by adding more switches, e.g.,
->use_arch_sysdata.

I think the design problem is that PCI host bridge drivers should
supply the PCI domain up front instead of having callbacks to extract
it.

We could put "int domain_nr" in struct pci_host_bridge, and the arch
code or host bridge driver (pcibios_init_hw(), *_pcie_probe(), VMD,
HV, etc) could fill in pci_host_bridge.domain_nr before calling
pci_scan_root_bus_bridge() or pci_host_probe().

Then maybe we could get rid of pci_bus_find_domain_nr() and some of
the needlessly arch-specific implementations of pci_domain_nr().
I think we likely could get rid of CONFIG_PCI_DOMAINS_GENERIC, too,
eventually.

Agreed. I actually still have a (not really tested) patch series to clean up
the pci host bridge registration, and this should make this a lot easier
to add on top.

I should dig that out of my backlog and post for review.

         Arnd