RE: [PATCH v3 5/5] guides/rawdevs: add description of ofs in ifpga doc

["Zhang, Tianfei" <tianfei.zhang@intel.com>]

> -----Original Message-----
> From: Huang, Wei <wei.huang@intel.com>
> Sent: Thursday, May 26, 2022 11:33 AM
> To: dev@dpdk.org; thomas@monjalon.net; nipun.gupta@nxp.com;
> hemant.agrawal@nxp.com
> Cc: stable@dpdk.org; Xu, Rosen <rosen.xu@intel.com>; Zhang, Tianfei
> <tianfei.zhang@intel.com>; Zhang, Qi Z <qi.z.zhang@intel.com>; Huang, Wei
> <wei.huang@intel.com>
> Subject: [PATCH v3 5/5] guides/rawdevs: add description of ofs in ifpga doc
> 
> OFS (Open FPGA Stack) specification is introduced briefly.
> 
> Signed-off-by: Wei Huang <wei.huang@intel.com>
> ---
>  doc/guides/rawdevs/ifpga.rst | 114
> ++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 113 insertions(+), 1 deletion(-)
> 
> diff --git a/doc/guides/rawdevs/ifpga.rst b/doc/guides/rawdevs/ifpga.rst index
> dbd0d6e..8809bfc 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 +100,115 @@ 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 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  |
> +     +-----------------+  +--------------+  +-------------+   +-----------+
> +
This diagram those Applications are DPDK application?

> +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.

This section is not mentioned for DPDK?

> +
> +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.

The same of above.

I think we can add a little description how to leverage the  virtualization for DPDK usage for PAC card.
> +
> +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                              |
> +                    +------------------------------------------+
> --
> 1.8.3.1