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Based on kernel version 3.16. Page generated on 2014-08-06 21:40 EST.

1			PCI Express I/O Virtualization Howto
2			Copyright (C) 2009 Intel Corporation
3			    Yu Zhao <yu.zhao@intel.com>
4	
5			Update: November 2012
6				-- sysfs-based SRIOV enable-/disable-ment
7			Donald Dutile <ddutile@redhat.com>
8	
9	1. Overview
10	
11	1.1 What is SR-IOV
12	
13	Single Root I/O Virtualization (SR-IOV) is a PCI Express Extended
14	capability which makes one physical device appear as multiple virtual
15	devices. The physical device is referred to as Physical Function (PF)
16	while the virtual devices are referred to as Virtual Functions (VF).
17	Allocation of the VF can be dynamically controlled by the PF via
18	registers encapsulated in the capability. By default, this feature is
19	not enabled and the PF behaves as traditional PCIe device. Once it's
20	turned on, each VF's PCI configuration space can be accessed by its own
21	Bus, Device and Function Number (Routing ID). And each VF also has PCI
22	Memory Space, which is used to map its register set. VF device driver
23	operates on the register set so it can be functional and appear as a
24	real existing PCI device.
25	
26	2. User Guide
27	
28	2.1 How can I enable SR-IOV capability
29	
30	Multiple methods are available for SR-IOV enablement.
31	In the first method, the device driver (PF driver) will control the
32	enabling and disabling of the capability via API provided by SR-IOV core.
33	If the hardware has SR-IOV capability, loading its PF driver would
34	enable it and all VFs associated with the PF.  Some PF drivers require
35	a module parameter to be set to determine the number of VFs to enable.
36	In the second method, a write to the sysfs file sriov_numvfs will
37	enable and disable the VFs associated with a PCIe PF.  This method
38	enables per-PF, VF enable/disable values versus the first method,
39	which applies to all PFs of the same device.  Additionally, the
40	PCI SRIOV core support ensures that enable/disable operations are
41	valid to reduce duplication in multiple drivers for the same
42	checks, e.g., check numvfs == 0 if enabling VFs, ensure
43	numvfs <= totalvfs.
44	The second method is the recommended method for new/future VF devices.
45	
46	2.2 How can I use the Virtual Functions
47	
48	The VF is treated as hot-plugged PCI devices in the kernel, so they
49	should be able to work in the same way as real PCI devices. The VF
50	requires device driver that is same as a normal PCI device's.
51	
52	3. Developer Guide
53	
54	3.1 SR-IOV API
55	
56	To enable SR-IOV capability:
57	(a) For the first method, in the driver:
58		int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn);
59		'nr_virtfn' is number of VFs to be enabled.
60	(b) For the second method, from sysfs:
61		echo 'nr_virtfn' > \
62	        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
63	
64	To disable SR-IOV capability:
65	(a) For the first method, in the driver:
66		void pci_disable_sriov(struct pci_dev *dev);
67	(b) For the second method, from sysfs:
68		echo  0 > \
69	        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
70	
71	3.2 Usage example
72	
73	Following piece of code illustrates the usage of the SR-IOV API.
74	
75	static int dev_probe(struct pci_dev *dev, const struct pci_device_id *id)
76	{
77		pci_enable_sriov(dev, NR_VIRTFN);
78	
79		...
80	
81		return 0;
82	}
83	
84	static void dev_remove(struct pci_dev *dev)
85	{
86		pci_disable_sriov(dev);
87	
88		...
89	}
90	
91	static int dev_suspend(struct pci_dev *dev, pm_message_t state)
92	{
93		...
94	
95		return 0;
96	}
97	
98	static int dev_resume(struct pci_dev *dev)
99	{
100		...
101	
102		return 0;
103	}
104	
105	static void dev_shutdown(struct pci_dev *dev)
106	{
107		...
108	}
109	
110	static int dev_sriov_configure(struct pci_dev *dev, int numvfs)
111	{
112		if (numvfs > 0) {
113			...
114			pci_enable_sriov(dev, numvfs);
115			...
116			return numvfs;
117		}
118		if (numvfs == 0) {
119			....
120			pci_disable_sriov(dev);
121			...
122			return 0;
123		}
124	}
125	
126	static struct pci_driver dev_driver = {
127		.name =		"SR-IOV Physical Function driver",
128		.id_table =	dev_id_table,
129		.probe =	dev_probe,
130		.remove =	dev_remove,
131		.suspend =	dev_suspend,
132		.resume =	dev_resume,
133		.shutdown =	dev_shutdown,
134		.sriov_configure = dev_sriov_configure,
135	};
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