OFS (Open FPGA Stack) specification is introduced briefly. Signed-off-by: Wei Huang <wei.hu...@intel.com> Reviewed-by: Rosen Xu <rosen...@intel.com> --- v2: update description per Tianfei's comment --- doc/guides/rawdevs/ifpga.rst | 105 ++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 104 insertions(+), 1 deletion(-)
diff --git a/doc/guides/rawdevs/ifpga.rst b/doc/guides/rawdevs/ifpga.rst index dbd0d6e..3dce57a 100644 --- a/doc/guides/rawdevs/ifpga.rst +++ b/doc/guides/rawdevs/ifpga.rst @@ -1,5 +1,5 @@ .. SPDX-License-Identifier: BSD-3-Clause - Copyright(c) 2018 Intel Corporation. + Copyright(c) 2018-2022 Intel Corporation. IFPGA Rawdev Driver ====================== @@ -100,3 +100,106 @@ The following device parameters are supported: If null, the AFU Bit Stream has been PR in FPGA, if not forces PR and identifies AFU Bit Stream file. + + +Open FPGA Stack +===================== + +Open FPGA Stack (OFS) is a collection of RTL and open source software providing +interfaces to access the instantiated RTL easily in an FPGA. OFS leverages the +DFL for the implementation of the FPGA RTL design. + +OFS designs allow for the arrangement of software interfaces across multiple +PCIe endpoints. Some of these interfaces may be PFs defined in the static region +that connect to interfaces in an IP that is loaded via Partial Reconfiguration (PR). +And some of these interfaces may be VFs defined in the PR region that can be +reconfigured by the end-user. Furthermore, these PFs/VFs may use DFLs such that +features may be discovered and accessed in user space with the aid of a generic +kernel driver like vfio-pci. The diagram below depicts an example design with one +PF and two VFs. In this example, it will export the management functions via PF0 +and acceleration functions via VF0 and VF1, leverage VFIO to export the MMIO space +to an application.:: + + +-----------------+ +-------------+ +------------+ + | FPGA Management | | DPDK App | | User App | + | App | | | | | + +--------+--------+ +------+------+ +-----+------+ + | | | + +--------+--------+ +------+------+ | + |IFPGA PMD driver | |AFU MF driver| | + +--------+--------+ +------+------+ | + | | | + +--------+------------------+---------------+------+ + | VFIO-PCI | + +--------+------------------+---------------+------+ + | | | + +--------+--------+ +------+------+ +----+------+ + | PF0 | | PF0_VF0 | | PF0_VF1 | + +-----------------+ +-------------+ +-----------+ + +As accelerators are specialized hardware, they are typically limited in the +number installed in a given system. Many use cases require them to be shared +across multiple software contexts or threads of software execution, either +through partitioning of individual dedicated resources, or virtualization of +shared resources. OFS provides several models to share the AFU resources via +PR mechanism and hardware-based virtualization schemes. + +1. Legacy model. + With legacy model FPGA cards like Intel PAC N3000 or N5000, there is + a notion that the boundary between the AFU and the shell is also the unit of + PR for those FPGA platforms. This model is only able to handle a + single context, because it only has one PR engine, and one PR region which + has an associated Port device. +2. Multiple VFs per PR slot. + In this model, available AFU resources may allow instantiation of many VFs + which have a dedicated PCIe function with their own dedicated MMIO space, or + partition a region of MMIO space on a single PCIe function. Intel PAC N6000 + card has implemented this model. + In this model, the AFU/PR slot was not connected to port device. For DFL's view, + the Next_AFU pointer in FIU feature header of port device points to NULL in this + model. On the other hand, each VF can start with an AFU feature header without + being connected to a FIU Port feature header. + +The VFs are created through the Linux kernel driver before we use them in DPDK. + +OFS provides the diversity for accessing the AFU resource to RTL developer. +An IP designer may choose to add more than one PF for interfacing with IP +on the FPGA and choose different model to access the AFU resource. + +There is one reference architecture design using the "Multiple VFs per PR slot" +model for OFS as illustrated below. In this reference design, it exports the +FPGA management functions via PF0. PF1 will bind with DPDK virtio driver +presenting itself as a network interface to the application. PF2 will bind to the +vfio-pci driver allowing the user space software to discover and interface +with the specific workload like diagnostic test. It leverages AFU PMD driver to +access the AFU resources in DPDK.:: + + +----------------------+ + | PF/VF mux/demux | + +--+--+-----+------+-+-+ + | | | | | + +------------------------+ | | | | + PF0 | +---------+ +-+ | | + +---+---+ | +---+----+ | | + | DFH | | | DFH | | | + +-------+ +-----+----+ +--------+ | | + | FME | | VirtIO | | Test | | | + +---+---+ +----------+ +--------+ | | + | PF1 PF2 | | + | | | + | +----------+ | + | | ++ + | | | + | | PF0_VF0 | PF0_VF1 + | +-----------------+-----------+------------+ + | | +-----+-----------+--------+ | + | | | | | | | + | | +------+ | +--+ -+ +--+---+ | | + | | | Port | | | DFH | | DFH | | | + +-----------+ +------+ | +-----+ +------+ | | + | | | DEV | | DEV | | | + | | +-----+ +------+ | | + | | PR Slot | | + | +--------------------------+ | + | Port Gasket | + +------------------------------------------+ -- 1.8.3.1
