1.. SPDX-License-Identifier: GPL-2.0
  2.. include:: <isonum.txt>
  3
  4====================================
  5PCI Express I/O Virtualization Howto
  6====================================
  7
  8:Copyright: |copy| 2009 Intel Corporation
  9:Authors: - Yu Zhao <yu.zhao@intel.com>
 10          - Donald Dutile <ddutile@redhat.com>
 11
 12Overview
 13========
 14
 15What is SR-IOV
 16--------------
 17
 18Single Root I/O Virtualization (SR-IOV) is a PCI Express Extended
 19capability which makes one physical device appear as multiple virtual
 20devices. The physical device is referred to as Physical Function (PF)
 21while the virtual devices are referred to as Virtual Functions (VF).
 22Allocation of the VF can be dynamically controlled by the PF via
 23registers encapsulated in the capability. By default, this feature is
 24not enabled and the PF behaves as traditional PCIe device. Once it's
 25turned on, each VF's PCI configuration space can be accessed by its own
 26Bus, Device and Function Number (Routing ID). And each VF also has PCI
 27Memory Space, which is used to map its register set. VF device driver
 28operates on the register set so it can be functional and appear as a
 29real existing PCI device.
 30
 31User Guide
 32==========
 33
 34How can I enable SR-IOV capability
 35----------------------------------
 36
 37Multiple methods are available for SR-IOV enablement.
 38In the first method, the device driver (PF driver) will control the
 39enabling and disabling of the capability via API provided by SR-IOV core.
 40If the hardware has SR-IOV capability, loading its PF driver would
 41enable it and all VFs associated with the PF.  Some PF drivers require
 42a module parameter to be set to determine the number of VFs to enable.
 43In the second method, a write to the sysfs file sriov_numvfs will
 44enable and disable the VFs associated with a PCIe PF.  This method
 45enables per-PF, VF enable/disable values versus the first method,
 46which applies to all PFs of the same device.  Additionally, the
 47PCI SRIOV core support ensures that enable/disable operations are
 48valid to reduce duplication in multiple drivers for the same
 49checks, e.g., check numvfs == 0 if enabling VFs, ensure
 50numvfs <= totalvfs.
 51The second method is the recommended method for new/future VF devices.
 52
 53How can I use the Virtual Functions
 54-----------------------------------
 55
 56The VF is treated as hot-plugged PCI devices in the kernel, so they
 57should be able to work in the same way as real PCI devices. The VF
 58requires device driver that is same as a normal PCI device's.
 59
 60Developer Guide
 61===============
 62
 63SR-IOV API
 64----------
 65
 66To enable SR-IOV capability:
 67
 68(a) For the first method, in the driver::
 69
 70	int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn);
 71
 72'nr_virtfn' is number of VFs to be enabled.
 73
 74(b) For the second method, from sysfs::
 75
 76	echo 'nr_virtfn' > \
 77        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
 78
 79To disable SR-IOV capability:
 80
 81(a) For the first method, in the driver::
 82
 83	void pci_disable_sriov(struct pci_dev *dev);
 84
 85(b) For the second method, from sysfs::
 86
 87	echo  0 > \
 88        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
 89
 90To enable auto probing VFs by a compatible driver on the host, run
 91command below before enabling SR-IOV capabilities. This is the
 92default behavior.
 93::
 94
 95	echo 1 > \
 96        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_drivers_autoprobe
 97
 98To disable auto probing VFs by a compatible driver on the host, run
 99command below before enabling SR-IOV capabilities. Updating this
100entry will not affect VFs which are already probed.
101::
102
103	echo  0 > \
104        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_drivers_autoprobe
105
106Usage example
107-------------
108
109Following piece of code illustrates the usage of the SR-IOV API.
110::
111
112	static int dev_probe(struct pci_dev *dev, const struct pci_device_id *id)
113	{
114		pci_enable_sriov(dev, NR_VIRTFN);
115
116		...
117
118		return 0;
119	}
120
121	static void dev_remove(struct pci_dev *dev)
122	{
123		pci_disable_sriov(dev);
124
125		...
126	}
127
128	static int dev_suspend(struct device *dev)
129	{
130		...
131
132		return 0;
133	}
134
135	static int dev_resume(struct device *dev)
136	{
137		...
138
139		return 0;
140	}
141
142	static void dev_shutdown(struct pci_dev *dev)
143	{
144		...
145	}
146
147	static int dev_sriov_configure(struct pci_dev *dev, int numvfs)
148	{
149		if (numvfs > 0) {
150			...
151			pci_enable_sriov(dev, numvfs);
152			...
153			return numvfs;
154		}
155		if (numvfs == 0) {
156			....
157			pci_disable_sriov(dev);
158			...
159			return 0;
160		}
161	}
162
163	static struct pci_driver dev_driver = {
164		.name =		"SR-IOV Physical Function driver",
165		.id_table =	dev_id_table,
166		.probe =	dev_probe,
167		.remove =	dev_remove,
168		.driver.pm =	&dev_pm_ops,
169		.shutdown =	dev_shutdown,
170		.sriov_configure = dev_sriov_configure,
171	};