[PATCH v5 5/5] guides/rawdevs: add description of ofs in ifpga doc

[Wei Huang <wei.huang@intel.com>]

OFS (Open FPGA Stack) specification is introduced briefly.

Signed-off-by: Wei Huang <wei.huang@intel.com>
Acked-by: Tianfei Zhang <tianfei.zhang@intel.com>
Reviewed-by: Rosen Xu <rosen.xu@intel.com>
---
v2: update description per Tianfei's comment
---
v3: update afu driver name in diagram
---
 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..bf557b2 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    |  |   AFU PMD   |        |
+     +--------+--------+  +------+------+        |
+              |                  |               |
+     +--------+------------------+---------------+------+
+     |                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