Re: [RFC v1 1/5] PCI: hv: Create and export hv_build_logical_dev_id()

Yu Zhang
2025-12-11T08:31:21Z

On Wed, Dec 10, 2025 at 03:39:45PM -0600, Bjorn Helgaas wrote:
> On Tue, Dec 09, 2025 at 01:11:24PM +0800, Yu Zhang wrote:
> > From: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>
> >
> > Hyper-V uses a logical device ID to identify a PCI endpoint device for
> > child partitions. This ID will also be required for future hypercalls
> > used by the Hyper-V IOMMU driver.
> >
> > Refactor the logic for building this logical device ID into a standalone
> > helper function and export the interface for wider use.
> >
> > Signed-off-by: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>
> > Signed-off-by: Yu Zhang <zhangyu1@linux.microsoft.com>
>
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
>
> > ---
> > drivers/pci/controller/pci-hyperv.c | 28 ++++++++++++++++++++--------
> > include/asm-generic/mshyperv.h | 2 ++
> > 2 files changed, 22 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> > index 146b43981b27..4b82e06b5d93 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -598,15 +598,31 @@ static unsigned int hv_msi_get_int_vector(struct irq_data *data)
> >
> > #define hv_msi_prepare pci_msi_prepare
> >
> > +/**
> > + * Build a "Device Logical ID" out of this PCI bus's instance GUID and the
> > + * function number of the device.
> > + */
> > +u64 hv_build_logical_dev_id(struct pci_dev *pdev)
> > +{
> > + struct pci_bus *pbus = pdev->bus;
> > + struct hv_pcibus_device *hbus = container_of(pbus->sysdata,
> > + struct hv_pcibus_device, sysdata);
> > +
> > + return (u64)((hbus->hdev->dev_instance.b[5] << 24) |
> > + (hbus->hdev->dev_instance.b[4] << 16) |
> > + (hbus->hdev->dev_instance.b[7] << 8) |
> > + (hbus->hdev->dev_instance.b[6] & 0xf8) |
> > + PCI_FUNC(pdev->devfn));
> > +}
> > +EXPORT_SYMBOL_GPL(hv_build_logical_dev_id);
> > +
> > /**
> > * hv_irq_retarget_interrupt() - "Unmask" the IRQ by setting its current
> > * affinity.
> > * @data: Describes the IRQ
> > *
> > * Build new a destination for the MSI and make a hypercall to
> > - * update the Interrupt Redirection Table. "Device Logical ID"
> > - * is built out of this PCI bus's instance GUID and the function
> > - * number of the device.
> > + * update the Interrupt Redirection Table.
> > */
> > static void hv_irq_retarget_interrupt(struct irq_data *data)
> > {
> > @@ -642,11 +658,7 @@ static void hv_irq_retarget_interrupt(struct irq_data *data)
> > params->int_entry.source = HV_INTERRUPT_SOURCE_MSI;
> > params->int_entry.msi_entry.address.as_uint32 = int_desc->address & 0xffffffff;
> > params->int_entry.msi_entry.data.as_uint32 = int_desc->data;
> > - params->device_id = (hbus->hdev->dev_instance.b[5] << 24) |
> > - (hbus->hdev->dev_instance.b[4] << 16) |
> > - (hbus->hdev->dev_instance.b[7] << 8) |
> > - (hbus->hdev->dev_instance.b[6] & 0xf8) |
> > - PCI_FUNC(pdev->devfn);
> > + params->device_id = hv_build_logical_dev_id(pdev);
> > params->int_target.vector = hv_msi_get_int_vector(data);
> >
> > if (hbus->protocol_version >= PCI_PROTOCOL_VERSION_1_2) {
> > diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> > index 64ba6bc807d9..1a205ed69435 100644
> > --- a/include/asm-generic/mshyperv.h
> > +++ b/include/asm-generic/mshyperv.h
> > @@ -71,6 +71,8 @@ extern enum hv_partition_type hv_curr_partition_type;
> > extern void * __percpu *hyperv_pcpu_input_arg;
> > extern void * __percpu *hyperv_pcpu_output_arg;
> >
> > +extern u64 hv_build_logical_dev_id(struct pci_dev *pdev);
>
> Curious why you would include the "extern" in this declaration? It's
> not *wrong*, but it's not necessary, and other declarations in this
> file omit it, e.g., the ones below:
>

Thank you, Bjorn.
Actually I don't think it is necessary. Will remove it in v2. :)

B.R.
Yu