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Date: Sun, 13 Mar 2022 09:32:05 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Tianfei Zhang <tianfei.zhang@...el.com>, hao.wu@...el.com,
trix@...hat.com, mdf@...nel.org, yilun.xu@...el.com,
linux-fpga@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: corbet@....net
Subject: Re: [PATCH v5 6/6] Documentation: fpga: dfl: add description of OFS
Hi--
On 3/13/22 03:52, Tianfei Zhang wrote:
> From: Tianfei zhang <tianfei.zhang@...el.com>
>
> This patch adds description about OFS support for DFL.
>
> ---
> 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..4c1f9cb82ccb 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
Add a space after the comma.
> + a notion that the boundary between the AFU and the shell is also the unit of
> + PR for those FPGA platforms. This model can only able to handle a
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 of VFs
of many VFs
> + which has a dedicated PCIe function with their own dedicated MMIO space, or
which have
or something different. I couldn't quite tell what is meant here.
> + 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 are no AFU MMIO region managed by
there is no
> + AFU driver. On the other hand, each VF can start with an AFU feature header without
> + connected to a FIU Port feature header.
being connected
or
connecting
> +
> +In multiple VFs per PR slot model, the port device can still be accessed using
> +ioctls API which expose by /dev/dfl-port.n device node, like port reset, get
which expose /dev/dfl-port.h device nodes,
> +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 no AFU MMIO space managed in AFU driver. Users can access the AFU resource
because there is no AFU MMIO space managed in the AFU driver.
> +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 enable VFs are compatible with
to enable VFs
> +legacy mode which mentioned in "FPGA virtualization - PCIe SRIOV" section
which are mentioned
> +in this documentation.
> +
> +OFS provides the diversity for access the AFU resource to RTL developer.
for accessing the AFU resource
> +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 bound to the
bind
> +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
--
~Randy
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