[PATCH v3 01/21] docs: fpga: add a document for Intel FPGA driver overview

[Wu Hao]

Add a document for Intel FPGA driver overview.

Signed-off-by: Enno Luebbers <enno.luebbers@xxxxxxxxx>
Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
Signed-off-by: Wu Hao <hao.wu@xxxxxxxxx>
----
v2: added FME fpga-mgr/bridge/region platform driver to driver organization.
    updated open discussion per current implementation.
    fixed some typos.
v3: use FPGA base region as container device instead of fpga-dev class.
    split common enumeration code from pcie driver to functions exposed by
    device feature list framework.
    update FME performance reporting which supports both integrated (iperf/)
    and discrete (dperf/) FPGA solutions.
---
 Documentation/fpga/intel-fpga.txt | 261 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 261 insertions(+)
 create mode 100644 Documentation/fpga/intel-fpga.txt

diff --git a/Documentation/fpga/intel-fpga.txt b/Documentation/fpga/intel-fpga.txt
new file mode 100644
index 0000000..0754733
--- /dev/null
+++ b/Documentation/fpga/intel-fpga.txt
@@ -0,0 +1,261 @@
+===============================================================================
+                    Intel FPGA driver Overview
+-------------------------------------------------------------------------------
+                Enno Luebbers <enno.luebbers@xxxxxxxxx>
+                Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
+                Wu Hao <hao.wu@xxxxxxxxx>
+
+The Intel FPGA driver provides interfaces for userspace applications to
+configure, enumerate, open, and access FPGA accelerators on platforms equipped
+with Intel(R) FPGA PCIe based solutions and enables system level management
+functions such as FPGA reconfiguration, power management, and virtualization.
+
+HW Architecture
+===============
+From the OS's point of view, the FPGA hardware appears as a regular PCIe device.
+The FPGA device memory is organized using a predefined data structure (Device
+Feature List). Features supported by the particular FPGA device are exposed
+through these data structures, as illustrated below:
+
+  +-------------------------------+  +-------------+
+  |              PF               |  |     VF      |
+  +-------------------------------+  +-------------+
+      ^            ^         ^              ^
+      |            |         |              |
++-----|------------|---------|--------------|-------+
+|     |            |         |              |       |
+|  +-----+     +-------+ +-------+      +-------+   |
+|  | FME |     | Port0 | | Port1 |      | Port2 |   |
+|  +-----+     +-------+ +-------+      +-------+   |
+|                  ^         ^              ^       |
+|                  |         |              |       |
+|              +-------+ +------+       +-------+   |
+|              |  AFU  | |  AFU |       |  AFU  |   |
+|              +-------+ +------+       +-------+   |
+|                                                   |
+|                 FPGA PCIe Device                  |
++---------------------------------------------------+
+
+The driver supports PCIe SR-IOV to create virtual functions (VFs) which can be
+used to assign individual accelerators to virtual machines.
+
+FME (FPGA Management Engine)
+============================
+The FPGA Management Engine performs power and thermal management, error
+reporting, reconfiguration, performance reporting for integrated and discrete
+solution, and other infrastructure functions. Each FPGA has one FME, which is
+always accessed through the physical function (PF).
+
+User-space applications can acquire exclusive access to the FME using open(),
+and release it using close().
+
+The following functions are exposed through ioctls:
+
+	Get driver API version (FPGA_GET_API_VERSION)
+	Check for extensions (FPGA_CHECK_EXTENSION)
+	Assign port to PF (FPGA_FME_PORT_ASSIGN)
+	Release port from PF (FPGA_FME_PORT_RELEASE)
+	Program bitstream (FPGA_FME_PORT_PR)
+
+More functions are exposed through sysfs
+(/sys/class/fpga_region/regionX/fpga-dfl-fme.n/):
+
+	Read bitstream ID (bitstream_id)
+	Read bitstream metadata (bitstream_metadata)
+	Read number of ports (ports_num)
+	Read socket ID (socket_id)
+	Read performance counters (iperf/ and dperf/)
+	Power management (power_mgmt/)
+	Thermal management (thermal_mgmt/)
+	Error reporting (errors/)
+
+PORT
+====
+A port represents the interface between the static FPGA fabric (the "blue
+bitstream") and a partially reconfigurable region containing an AFU (the "green
+bitstream"). It controls the communication from SW to the accelerator and
+exposes features such as reset and debug.
+
+A PCIe device may have several ports and each port can be released from PF by
+FPGA_FME_PORT_RELEASE ioctl on FME, and exposed through a VF via PCIe sriov
+sysfs interface.
+
+AFU
+===
+An AFU is attached to a port and exposes a 256k MMIO region to be used for
+accelerator-specific control registers.
+
+User-space applications can acquire exclusive access to an AFU attached to a
+port by using open() on the port device node, and release it using close().
+
+The following functions are exposed through ioctls:
+
+	Get driver API version (FPGA_GET_API_VERSION)
+	Check for extensions (FPGA_CHECK_EXTENSION)
+	Get port info (FPGA_PORT_GET_INFO)
+	Get MMIO region info (FPGA_PORT_GET_REGION_INFO)
+	Map DMA buffer (FPGA_PORT_DMA_MAP)
+	Unmap DMA buffer (FPGA_PORT_DMA_UNMAP)
+	Reset AFU (FPGA_PORT_RESET)
+	Enable UMsg (FPGA_PORT_UMSG_ENABLE)
+	Disable UMsg (FPGA_PORT_UMSG_DISABLE)
+	Set UMsg mode (FPGA_PORT_UMSG_SET_MODE)
+	Set UMsg base address (FPGA_PORT_UMSG_SET_BASE_ADDR)
+
+User-space applications can also mmap() accelerator MMIO regions.
+
+More functions are exposed through sysfs:
+(/sys/class/fpga_region/<regionX>/<fpga-dfl-port.m>/):
+
+	Read Accelerator GUID (afu_id)
+	Error reporting (errors/)
+
+Partial Reconfiguration
+=======================
+As mentioned above, accelerators can be reconfigured through partial
+reconfiguration of a green bitstream file (GBS). The green bitstream must have
+been generated for the exact blue bitstream and targeted reconfigurable region
+(port) of the FPGA; otherwise, the reconfiguration operation will fail and
+possibly cause system instability. This compatibility can be checked by
+comparing the interface ID noted in the GBS header against the interface ID
+exposed by the FME through sysfs (see above). This check is usually done by
+user-space before calling the reconfiguration IOCTL.
+
+FPGA virtualization
+===================
+To enable accessing an accelerator from applications running in a VM, the
+respective AFU's port needs to be assigned to a VF using the following steps:
+
+ a) The PF owns all AFU ports by default. Any port that needs to be reassigned
+ to a VF must first be released through the FPGA_FME_PORT_RELEASE ioctl on the
+ FME device.
+
+ b) Once N ports are released from PF, then user can use command below to
+ enable SRIOV and VFs. Each VF owns only one Port with AFU.
+
+ echo N > $PCI_DEVICE_PATH/sriov_numvfs
+
+ c) Pass through the VFs to VMs
+
+ d) The AFU under VF is accessible from applications in VM (using the same
+ driver inside the VF).
+
+Note that an FME can't be assigned to a VF, thus PR and other management
+functions are only available via the PF.
+
+
+Driver organization
+===================
+
+  +-------++------++------+             |
+  | FME   || FME  || FME  |             |
+  | FPGA  || FPGA || FPGA |             |
+  |Manager||Bridge||Region|             |
+  +-------++------++------+             |
+  +-----------------------+  +--------+ |             +--------+
+  |          FME          |  |  AFU   | |             |  AFU   |
+  |         Module        |  | Module | |             | Module |
+  +-----------------------+  +--------+ |             +--------+
+        +-----------------------+       |       +-----------------------+
+        | FPGA Container Device |       |       | FPGA Container Device |
+        |  (FPGA Base Region)   |       |       |  (FPGA Base Region)   |
+        +-----------------------+       |       +-----------------------+
+          +------------------+          |         +------------------+
+          | FPGA PCIE Module |          | Virtual | FPGA PCIE Module |
+          +------------------+   Host   | Machine +------------------+
+ -------------------------------------- | ------------------------------
+           +---------------+            |          +---------------+
+           | PCI PF Device |            |          | PCI VF Device |
+           +---------------+            |          +---------------+
+
+The FPGA devices appear as regular PCIe devices; thus, the FPGA PCIe device
+driver is always loaded first once a FPGA PCIE PF or VF device is detected. This
+driver plays an infrastructural role in the driver architecture.  It:
+
+	a) locates the Device Feature Lists in PCIE device BAR memory, handles
+	   them and related resources to common interfaces from DFL framework
+	   for enumeration.
+	b) supports SRIOV.
+
+The feature device infrastructure provides common interfaces to create container
+device (FPGA base region), discover feature devices and their sub features from
+the given Device Feature Lists, and create platform devices for feature devices
+with related resources under the container device. It also abstracts operations
+for sub features and exposes common interfaces to feature device drivers.
+
+The FPGA Management Engine (FME) driver is a platform driver which is loaded
+automatically after FME platform device creation from the PCIE driver. It
+provides the key features for FPGA management, including:
+
+	a) Power and thermal management, error reporting, performance reporting
+	   and other infrastructure functions. Users can access these functions
+	   via sysfs interfaces exposed by FME driver.
+	b) Partial Reconfiguration. The FME driver creates FPGA manager, FPGA
+	   bridges and FPGA regions during PR sub feature initialization; Once
+	   it receives an FPGA_FME_PORT_PR ioctl from user, it invokes the
+	   common interface function from FPGA Region to complete the partial
+	   reconfiguration of the bitstream to the given port.
+	c) Port management for virtualization. The FME driver introduces two
+	   ioctls, FPGA_FME_PORT_RELEASE (releases given port from PF) and
+	   FPGA_FME_PORT_ASSIGN (assigns the port back to PF). Once the port is
+	   released from the PF, it can be assigned to the VF through the SRIOV
+	   interfaces provided by PCIE driver. (Refer to "FPGA virtualization"
+	   for more details).
+
+Similar to the the FME driver, the FPGA Accelerated Function Unit (AFU) driver
+is probed once the AFU platform device is created. The main function of this
+module is to provide an interface for userspace applications to access the
+individual accelerators, including basic reset control on port, AFU MMIO region
+export, dma buffer mapping service, UMsg notification, and remote debug
+functions (see above).
+
+
+Device enumeration
+==================
+This section introduces how applications enumerate the fpga device from
+the sysfs hierarchy under /sys/class/fpga_region.
+
+In the example below, two Intel(R) FPGA devices are installed in the host. Each
+fpga device has one FME and two ports (AFUs).
+
+FPGA regions are created under /sys/class/fpga_region/
+
+	/sys/class/fpga_region/region0
+	/sys/class/fpga_region/region1
+	/sys/class/fpga_region/region2
+	...
+
+Application needs to search each regionX folder, if feature device is found,
+(e.g "fpga-dfl-port.n" or "fpga-dfl-fme.m" is found), then it's the base
+fpga region which represents the FPGA device.
+
+Each base region has one FME and two ports (AFUs) as child devices:
+
+	/sys/class/fpga_region/region0/fpga-dfl-fme.0
+	/sys/class/fpga_region/region0/fpga-dfl-port.0
+	/sys/class/fpga_region/region0/fpga-dfl-port.1
+	...
+
+	/sys/class/fpga_region/region3/fpga-dfl-fme.1
+	/sys/class/fpga_region/region3/fpga-dfl-port.2
+	/sys/class/fpga_region/region3/fpga-dfl-port.3
+	...
+
+In general, the FME/AFU sysfs interfaces are named as follows:
+
+	/sys/class/fpga_region/<regionX>/<fpga-dfl-fme.n>/
+	/sys/class/fpga_region/<regionX>/<fpga-dfl-port.m>/
+
+with 'n' consecutively numbering all FMEs and 'm' consecutively numbering all
+ports.
+
+The device nodes used for ioctl() or mmap() can be referenced through:
+
+	/sys/class/fpga_region/<regionX>/<fpga-dfl-fme.n>/dev
+	/sys/class/fpga_region/<regionX>/<fpga-dfl-port.n>/dev
+
+Open discussion
+===============
+FME driver exports one ioctl (FPGA_FME_PORT_PR) for partial reconfiguration to
+user now. In the future, if unified user interfaces for reconfiguration are
+added, FME driver should switch to them from ioctl interface.
-- 
1.8.3.1