RE: [PATCH v2 1/2] PCI: Enable host bridge emulation for PCI_DOMAINS_GENERIC platforms

[<dan.j.williams@intel.com>]

Michael Kelley wrote:
> From: Dan Williams <dan.j.williams@intel.com> Sent: Friday, October 24, 2025 3:46 PM
> > 
> > The ability to emulate a host bridge is useful not only for hardware PCI
> > controllers like CONFIG_VMD, or virtual PCI controllers like
> > CONFIG_PCI_HYPERV, but also for test and development scenarios like
> > CONFIG_SAMPLES_DEVSEC [1].
> > 
> > One stumbling block for defining CONFIG_SAMPLES_DEVSEC, a sample
> > implementation of a platform TSM for PCI Device Security, is the need to
> > accommodate PCI_DOMAINS_GENERIC architectures alongside x86 [2].
> 
> There's not a [2] tag anywhere below.  Presumably it should be the "Closes:"
> link?

Yes, good catch.

> > In support of supplementing the existing CONFIG_PCI_BRIDGE_EMUL
> > infrastructure for host bridges:
> > 
> > * Introduce pci_bus_find_emul_domain_nr() as a common way to find a free
> >   PCI domain number whether that is to reuse the existing dynamic
> >   allocation code in the !ACPI case, or to assign an unused domain above
> >   the last ACPI segment.
> > 
> > * Convert pci-hyperv to the new allocator so that the PCI core can
> >   unconditionally assume that bridge->domain_nr != PCI_DOMAIN_NR_NOT_SET
> >   is the dynamically allocated case.
> > 
> > A follow on patch can also convert vmd to the new scheme. Currently vmd
> > is limited to CONFIG_PCI_DOMAINS_GENERIC=n (x86) so, unlike pci-hyperv,
> > it does not immediately conflict with this new
> > pci_bus_find_emul_domain_nr() mechanism.
> > 
> > Link: https://lore.kernel.org/all/174107249038.1288555.12362100502109498455.stgit@dwillia2-xfh.jf.intel.com [1]
> > Reported-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Closes: https://lore.kernel.org/all/20250311144601.145736-3-suzuki.poulose@arm.com 
> > Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
> > Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > Cc: Rob Herring <robh@kernel.org>
> > Cc: Bjorn Helgaas <bhelgaas@google.com>
> > Cc: "K. Y. Srinivasan" <kys@microsoft.com>
> > Cc: Haiyang Zhang <haiyangz@microsoft.com>
> > Cc: Wei Liu <wei.liu@kernel.org>
> > Cc: Dexuan Cui <decui@microsoft.com>
> > Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > [michael: maintain compatibility with userspace that expects 16-bit ids]
> 
> Is the above line spurious?  It doesn't seem to belong here.

That was documenting the change to make the @max argument to
pci_bus_find_emul_domain_nr() be U16_MAX in the Hyper-V case, but yeah
no need to note that in this case. You did not edit the patch directly.
I am ok if Bjorn deletes that on applying.

If you want a respin Bjorn, let me know.

> > Cc: Michael Kelley <mhklinux@outlook.com>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> 
> Tested on x86 and arm64 VMs in the Azure public cloud with
> multiple Hyper-V virtual PCI devices in each VM. So covered
> both the "CONFIG_PCI_DOMAINS_GENERIC=n" and "=y" cases.
> Did manual unbind/rebind of vPCI devices multiple times so the
> domain numbers would be freed and reallocated. All was good.
> I did not go to the trouble of simulating a domain number
> collision.
> 
> Reviewed-by: Michael Kelley <mhklinux@outlook.com>
> Tested-by: Michael Kelley <mhklinux@outlook.com>

Thanks, Michael much appreciated!