Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 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 To enable auto probing VFs by a compatible driver on the host, run 72 command below before enabling SR-IOV capabilities. This is the 73 default behavior. 74 echo 1 > \ 75 /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_drivers_autoprobe 76 77 To disable auto probing VFs by a compatible driver on the host, run 78 command below before enabling SR-IOV capabilities. Updating this 79 entry will not affect VFs which are already probed. 80 echo 0 > \ 81 /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_drivers_autoprobe 82 83 3.2 Usage example 84 85 Following piece of code illustrates the usage of the SR-IOV API. 86 87 static int dev_probe(struct pci_dev *dev, const struct pci_device_id *id) 88 { 89 pci_enable_sriov(dev, NR_VIRTFN); 90 91 ... 92 93 return 0; 94 } 95 96 static void dev_remove(struct pci_dev *dev) 97 { 98 pci_disable_sriov(dev); 99 100 ... 101 } 102 103 static int dev_suspend(struct pci_dev *dev, pm_message_t state) 104 { 105 ... 106 107 return 0; 108 } 109 110 static int dev_resume(struct pci_dev *dev) 111 { 112 ... 113 114 return 0; 115 } 116 117 static void dev_shutdown(struct pci_dev *dev) 118 { 119 ... 120 } 121 122 static int dev_sriov_configure(struct pci_dev *dev, int numvfs) 123 { 124 if (numvfs > 0) { 125 ... 126 pci_enable_sriov(dev, numvfs); 127 ... 128 return numvfs; 129 } 130 if (numvfs == 0) { 131 .... 132 pci_disable_sriov(dev); 133 ... 134 return 0; 135 } 136 } 137 138 static struct pci_driver dev_driver = { 139 .name = "SR-IOV Physical Function driver", 140 .id_table = dev_id_table, 141 .probe = dev_probe, 142 .remove = dev_remove, 143 .suspend = dev_suspend, 144 .resume = dev_resume, 145 .shutdown = dev_shutdown, 146 .sriov_configure = dev_sriov_configure, 147 };