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Date: Thu, 17 Mar 2022 08:36:21 +0000
From: "Wu, Hao" <hao.wu@...el.com>
To: "Zhang, Tianfei" <tianfei.zhang@...el.com>,
"trix@...hat.com" <trix@...hat.com>,
"mdf@...nel.org" <mdf@...nel.org>,
"Xu, Yilun" <yilun.xu@...el.com>,
"linux-fpga@...r.kernel.org" <linux-fpga@...r.kernel.org>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"rdunlap@...radead.org" <rdunlap@...radead.org>
CC: "corbet@....net" <corbet@....net>
Subject: RE: [PATCH v6 6/6] Documentation: fpga: dfl: add description of OFS
> Subject: [PATCH v6 6/6] Documentation: fpga: dfl: add description of OFS
>
> From: Tianfei zhang <tianfei.zhang@...el.com>
>
> This patch adds description about OFS support for DFL.
I think another major extension is for SRIOV support, DFL needs to be extended to support
another SRIOV usage model, could we have some more descriptions for that?
e.g. In the new usage model, that PORT is not turned into VF and still can be accessed
in PF? how port release will be handled (or ignored) in this new model?
>
> ---
> 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@...el.com>
> ---
> 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
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