From: Tianfei zhang <tianfei.zhang@xxxxxxxxx> This patch adds description about OFS support for DFL. --- v6: fix documentation with Randy's comment. v5: fix documentation with Matthew and Randy's comment. v4: add description about access the AFU on "multiple VFs per PR slot" model. v3: change IOFS to OFS in documentation. v2: * Fixs some typos. * Adds more detail description about the models of AFU access which supported in OFS. Signed-off-by: Tianfei zhang <tianfei.zhang@xxxxxxxxx> --- Documentation/fpga/dfl.rst | 114 +++++++++++++++++++++++++++++++++++++ 1 file changed, 114 insertions(+) diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst index ef9eec71f6f3..93f262fe7b8c 100644 --- a/Documentation/fpga/dfl.rst +++ b/Documentation/fpga/dfl.rst @@ -556,6 +556,120 @@ new DFL feature via UIO direct access, its feature id should be added to the driver's id_table. +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 two +PFs and two VFs. In this example, it will export the management functions via PF0, +PF1 will bind with virtio-net driver presenting itself as a network interface to +the OS. The other functions, VF0 and VF1, leverage VFIO to export the MMIO space +to an application or assign to a VM. +:: + + +-----------------+ +--------------+ +-------------+ +------------+ + | FPGA Management | | VirtIO | | User App | | Virtual | + | App | | App | | | | Machine | + +--------+--------+ +------+-------+ +------+------+ +-----+------+ + | | | | + +--------+--------+ +------+-------+ +------+------+ | + | DFL Driver | |VirtIO driver | | VFIO | | + +--------+--------+ +------+-------+ +------+------+ | + | | | | + | | | | + +--------+--------+ +------+-------+ +------+------+ +----+------+ + | PF0 | | PF1 | | 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, so in AFU driver perspective, there is no AFU MMIO region managed by + AFU driver. On the other hand, each VF can start with an AFU feature header without + being connected to a FIU Port feature header. + +In multiple VFs per PR slot model, the port device can still be accessed using +ioctls API which expose /dev/dfl-port.h device nodes, like port reset, get +port info, whose APIs were mentioned in AFU section in this documentation. But +it cannot access the AFU MMIO space via AFU ioctl APIs like DFL_FPGA_PORT_DMA_MAP +because there is no AFU MMIO space managed in the AFU driver. Users can access +the AFU resource by creating VF devices via PCIe SRIOV interface, and then access +the VF via VFIO driver or assign the VF to VM. + +In multiple VFs per PR slot model, the steps to enable VFs are compatible with +legacy mode which are mentioned in "FPGA virtualization - PCIe SRIOV" section +in this documentation. + +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 virtio-net driver +presenting itself as a network interface to the OS. PF2 will bind to the +vfio-pci driver allowing the user space software to discover and interface +with the specific workload like diagnostic test. To access the AFU resource, +it uses SR-IOV to partition workload interfaces across various VFs. +:: + + +----------------------+ + | 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 | + +------------------------------------------+ + + Open discussion =============== FME driver exports one ioctl (DFL_FPGA_FME_PORT_PR) for partial reconfiguration -- 2.26.2
