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+ PCI Express I/O Virtualization Howto
+ Copyright (C) 2009 Intel Corporation
+ Yu Zhao <yu.zhao@intel.com>
+
+ Update: November 2012
+ -- sysfs-based SRIOV enable-/disable-ment
+ Donald Dutile <ddutile@redhat.com>
+
+1. Overview
+
+1.1 What is SR-IOV
+
+Single Root I/O Virtualization (SR-IOV) is a PCI Express Extended
+capability which makes one physical device appear as multiple virtual
+devices. The physical device is referred to as Physical Function (PF)
+while the virtual devices are referred to as Virtual Functions (VF).
+Allocation of the VF can be dynamically controlled by the PF via
+registers encapsulated in the capability. By default, this feature is
+not enabled and the PF behaves as traditional PCIe device. Once it's
+turned on, each VF's PCI configuration space can be accessed by its own
+Bus, Device and Function Number (Routing ID). And each VF also has PCI
+Memory Space, which is used to map its register set. VF device driver
+operates on the register set so it can be functional and appear as a
+real existing PCI device.
+
+2. User Guide
+
+2.1 How can I enable SR-IOV capability
+
+Multiple methods are available for SR-IOV enablement.
+In the first method, the device driver (PF driver) will control the
+enabling and disabling of the capability via API provided by SR-IOV core.
+If the hardware has SR-IOV capability, loading its PF driver would
+enable it and all VFs associated with the PF. Some PF drivers require
+a module parameter to be set to determine the number of VFs to enable.
+In the second method, a write to the sysfs file sriov_numvfs will
+enable and disable the VFs associated with a PCIe PF. This method
+enables per-PF, VF enable/disable values versus the first method,
+which applies to all PFs of the same device. Additionally, the
+PCI SRIOV core support ensures that enable/disable operations are
+valid to reduce duplication in multiple drivers for the same
+checks, e.g., check numvfs == 0 if enabling VFs, ensure
+numvfs <= totalvfs.
+The second method is the recommended method for new/future VF devices.
+
+2.2 How can I use the Virtual Functions
+
+The VF is treated as hot-plugged PCI devices in the kernel, so they
+should be able to work in the same way as real PCI devices. The VF
+requires device driver that is same as a normal PCI device's.
+
+3. Developer Guide
+
+3.1 SR-IOV API
+
+To enable SR-IOV capability:
+(a) For the first method, in the driver:
+ int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn);
+ 'nr_virtfn' is number of VFs to be enabled.
+(b) For the second method, from sysfs:
+ echo 'nr_virtfn' > \
+ /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
+
+To disable SR-IOV capability:
+(a) For the first method, in the driver:
+ void pci_disable_sriov(struct pci_dev *dev);
+(b) For the second method, from sysfs:
+ echo 0 > \
+ /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
+
+3.2 Usage example
+
+Following piece of code illustrates the usage of the SR-IOV API.
+
+static int dev_probe(struct pci_dev *dev, const struct pci_device_id *id)
+{
+ pci_enable_sriov(dev, NR_VIRTFN);
+
+ ...
+
+ return 0;
+}
+
+static void dev_remove(struct pci_dev *dev)
+{
+ pci_disable_sriov(dev);
+
+ ...
+}
+
+static int dev_suspend(struct pci_dev *dev, pm_message_t state)
+{
+ ...
+
+ return 0;
+}
+
+static int dev_resume(struct pci_dev *dev)
+{
+ ...
+
+ return 0;
+}
+
+static void dev_shutdown(struct pci_dev *dev)
+{
+ ...
+}
+
+static int dev_sriov_configure(struct pci_dev *dev, int numvfs)
+{
+ if (numvfs > 0) {
+ ...
+ pci_enable_sriov(dev, numvfs);
+ ...
+ return numvfs;
+ }
+ if (numvfs == 0) {
+ ....
+ pci_disable_sriov(dev);
+ ...
+ return 0;
+ }
+}
+
+static struct pci_driver dev_driver = {
+ .name = "SR-IOV Physical Function driver",
+ .id_table = dev_id_table,
+ .probe = dev_probe,
+ .remove = dev_remove,
+ .suspend = dev_suspend,
+ .resume = dev_resume,
+ .shutdown = dev_shutdown,
+ .sriov_configure = dev_sriov_configure,
+};
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