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diff --git a/Documentation/PCI/pci-iov-howto.rst b/Documentation/PCI/pci-iov-howto.rst new file mode 100644 index 000000000..b9fd00320 --- /dev/null +++ b/Documentation/PCI/pci-iov-howto.rst @@ -0,0 +1,172 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: <isonum.txt> + +==================================== +PCI Express I/O Virtualization Howto +==================================== + +:Copyright: |copy| 2009 Intel Corporation +:Authors: - Yu Zhao <yu.zhao@intel.com> + - Donald Dutile <ddutile@redhat.com> + +Overview +======== + +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. + +User Guide +========== + +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. + +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. + +Developer Guide +=============== + +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 + +To enable auto probing VFs by a compatible driver on the host, run +command below before enabling SR-IOV capabilities. This is the +default behavior. +:: + + echo 1 > \ + /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_drivers_autoprobe + +To disable auto probing VFs by a compatible driver on the host, run +command below before enabling SR-IOV capabilities. Updating this +entry will not affect VFs which are already probed. +:: + + echo 0 > \ + /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_drivers_autoprobe + +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, + }; |