From: Knut Omang <knut.om...@oracle.com>
Add a small intro + minimal documentation for how to
implement SR/IOV support for an emulated device.
Signed-off-by: Knut Omang <kn...@ifi.uio.no>
---
docs/pcie_sriov.txt | 115 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 115 insertions(+)
create mode 100644 docs/pcie_sriov.txt
diff --git a/docs/pcie_sriov.txt b/docs/pcie_sriov.txt
new file mode 100644
index 0000000000..f5e891e1d4
--- /dev/null
+++ b/docs/pcie_sriov.txt
@@ -0,0 +1,115 @@
+PCI SR/IOV EMULATION SUPPORT
+============================
+
+Description
+===========
+SR/IOV (Single Root I/O Virtualization) is an optional extended capability
+of a PCI Express device. It allows a single physical function (PF) to appear
as multiple
+virtual functions (VFs) for the main purpose of eliminating software
+overhead in I/O from virtual machines.
+
+Qemu now implements the basic common functionality to enable an emulated device
+to support SR/IOV. Yet no fully implemented devices exists in Qemu, but a
+proof-of-concept hack of the Intel igb can be found here:
+
+git://github.com/knuto/qemu.git sriov_patches_v5
+
+Implementation
+==============
+Implementing emulation of an SR/IOV capable device typically consists of
+implementing support for two types of device classes; the "normal" physical
device
+(PF) and the virtual device (VF). From Qemu's perspective, the VFs are just
+like other devices, except that some of their properties are derived from
+the PF.
+
+A virtual function is different from a physical function in that the BAR
+space for all VFs are defined by the BAR registers in the PFs SR/IOV
+capability. All VFs have the same BARs and BAR sizes.
+
+Accesses to these virtual BARs then is computed as
+
+ <VF BAR start> + <VF number> * <BAR sz> + <offset>
+
+From our emulation perspective this means that there is a separate call for
+setting up a BAR for a VF.
+
+1) To enable SR/IOV support in the PF, it must be a PCI Express device so
+ you would need to add a PCI Express capability in the normal PCI
+ capability list. You might also want to add an ARI (Alternative
+ Routing-ID Interpretation) capability to indicate that your device
+ supports functions beyond it's "own" function space (0-7),
+ which is necessary to support more than 7 functions, or
+ if functions extends beyond offset 7 because they are placed at an
+ offset > 1 or have stride > 1.
+
+ ...
+ #include "hw/pci/pcie.h"
+ #include "hw/pci/pcie_sriov.h"
+
+ pci_your_pf_dev_realize( ... )
+ {
+ ...
+ int ret = pcie_endpoint_cap_init(d, 0x70);
+ ...
+ pcie_ari_init(d, 0x100, 1);
+ ...
+
+ /* Add and initialize the SR/IOV capability */
+ pcie_sriov_pf_init(d, 0x200, "your_virtual_dev",
+ vf_devid, initial_vfs, total_vfs,
+ fun_offset, stride);
+
+ /* Set up individual VF BARs (parameters as for normal BARs) */
+ pcie_sriov_pf_init_vf_bar( ... )
+ ...
+ }
+
+ For cleanup, you simply call:
+
+ pcie_sriov_pf_exit(device);
+
+ which will delete all the virtual functions and associated resources.
+
+2) Similarly in the implementation of the virtual function, you need to
+ make it a PCI Express device and add a similar set of capabilities
+ except for the SR/IOV capability. Then you need to set up the VF BARs as
+ subregions of the PFs SR/IOV VF BARs by calling
+ pcie_sriov_vf_register_bar() instead of the normal pci_register_bar() call:
+
+ pci_your_vf_dev_realize( ... )
+ {
+ ...
+ int ret = pcie_endpoint_cap_init(d, 0x60);
+ ...
+ pcie_ari_init(d, 0x100, 1);
+ ...
+ memory_region_init(mr, ... )
+ pcie_sriov_vf_register_bar(d, bar_nr, mr);
+ ...
+ }
+
+Testing on Linux guest
+======================
+The easiest is if your device driver supports sysfs based SR/IOV
+enabling. Support for this was added in kernel v.3.8, so not all drivers
+support it yet.
+
+To enable 4 VFs for a device at 01:00.0:
+
+ modprobe yourdriver
+ echo 4 > /sys/bus/pci/devices/0000:01:00.0/sriov_numvfs
+
+You should now see 4 VFs with lspci.
+To turn SR/IOV off again - the standard requires you to turn it off before you
can enable
+another VF count, and the emulation enforces this:
+
+ echo 0 > /sys/bus/pci/devices/0000:01:00.0/sriov_numvfs
+
+Older drivers typically provide a max_vfs module parameter
+to enable it at load time:
+
+ modprobe yourdriver max_vfs=4
+
+To disable the VFs again then, you simply have to unload the driver:
+
+ rmmod yourdriver
--
2.25.1
