linux-kernel - Re: [RFC v1 1/5] PCI: hv: Create and export hv_build_logical_dev

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Message-ID: <oqpivhhbgcc3hcmkq3cumn6d7rxxjgqmmdwlfpejjo2ztsth6u@ejhydql5xmsx>
Date: Thu, 11 Dec 2025 16:31:18 +0800
From: Yu Zhang <zhangyu1@...ux.microsoft.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org, 
	iommu@...ts.linux.dev, linux-pci@...r.kernel.org, kys@...rosoft.com, 
	haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com, lpieralisi@...nel.org, 
	kwilczynski@...nel.org, mani@...nel.org, robh@...nel.org, bhelgaas@...gle.com, 
	arnd@...db.de, joro@...tes.org, will@...nel.org, robin.murphy@....com, 
	easwar.hariharan@...ux.microsoft.com, jacob.pan@...ux.microsoft.com, nunodasneves@...ux.microsoft.com, 
	mrathor@...ux.microsoft.com, mhklinux@...look.com, peterz@...radead.org, 
	linux-arch@...r.kernel.org
Subject: Re: [RFC v1 1/5] PCI: hv: Create and export hv_build_logical_dev_id()

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@...ux.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@...ux.microsoft.com>
> > Signed-off-by: Yu Zhang <zhangyu1@...ux.microsoft.com>
> 
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.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