How do PCIe devices advertise multiple virtual functions to Linux?

Question

SR-IOV lets PCIe devices expose a single physical function and multiple virtual functions. How does the kernel detect that a device supports virtual functions? Is it a part of the PCIe configuration registers? Where in the kernel are devices tested for how many functions they export?

EDIT: I'm looking for a line of code (or a file) in the kernel source that inspects a PCIe device in order to determine how many virtual functions it exports. I'd also settle for a link to the appropriate standard that lays out what information a device needs to send to the host in order to report that it supports multiple virtual functions.

score 2 · Accepted Answer · answered Feb 17 '18 at 05:53

2

An SR-IOV capable device defines the SR-IOV Capability (extended capability ID 10h).

This is specified in chapter 9 of the PCI Express Base specification revision 4.0. I'm not sure whether you can find a free copy online; you may need to be a PCI-SIG member.

In the Linux kernel, look for PCI_EXT_CAP_ID_SRIOV and PCI_SRIOV_TOTAL_VF in drivers/pci/iov.c.

answered Feb 17 '18 at 05:53

prl

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Perfect, exactly what I was looking for. Thanks! – Patrick Collins Feb 19 '18 at 21:14
Looking at a version of the "PCI Express Base Specification revision 4 ver 0.3," I see chapter 9 as "Physical Layer Electrical Sub-block Specification." Do I have the wrong document? – Patrick Collins Feb 20 '18 at 01:50
Oh, now that I have "ver 1.0" I see the section you're talking about -- "Single Root I/O Virtualization and Sharing" – Patrick Collins Feb 20 '18 at 02:02

How do PCIe devices advertise multiple virtual functions to Linux?

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