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Subject[PATCH v5 01/28] docs: fpga: add a document for FPGA Device Feature List (DFL) Framework Overview
Add a document for FPGA Device Feature List (DFL) Framework Overview.

Signed-off-by: Enno Luebbers <>
Signed-off-by: Xiao Guangrong <>
Signed-off-by: Wu Hao <>
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.
v4: rename this doc to Device Feature List (DFL) Framework Overview (dfl.txt)
add Device Feature List introduction and re-organize the content.
add description for port reset, bitstream_id/metadata and etc.
v5: remove introduction of the APIs/features which aren't covered in this patchset.
replace "blue/green bitstream" terminology with "static region" and "PR bitstream".
add a "DFL_" prefix to IOCTL APIs introduced by DFL framework.
s/FPGA Bus Device Module/FPGA DFL Device Module/
fix typos, improve descriptions per comments from Alan Tull against v4.
Documentation/fpga/dfl.txt | 285 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 285 insertions(+)
create mode 100644 Documentation/fpga/dfl.txt

diff --git a/Documentation/fpga/dfl.txt b/Documentation/fpga/dfl.txt
new file mode 100644
index 0000000..ba2a1ee
--- /dev/null
+++ b/Documentation/fpga/dfl.txt
@@ -0,0 +1,285 @@
+ FPGA Device Feature List (DFL) Framework Overview
+ Enno Luebbers <>
+ Xiao Guangrong <>
+ Wu Hao <>
+The Device Feature List (DFL) FPGA framework (and drivers according to this
+this framework) hides the very details of low layer hardwares and provides
+unified interfaces to userspace. Applications could use these interfaces to
+configure, enumerate, open and access FPGA accelerators on platforms which
+implemented the DFL in the device memory. Besides this, the DFL framework
+enables system level management functions such as FPGA reconfiguration.
+Device Feature List (DFL) Overview
+Device Feature List (DFL) defines a linked list of feature headers within the
+device MMIO space to provide an extensible way of adding features. Software can
+walk through these predefined data structures to enumerate FPGA features:
+FPGA Interface Unit (FIU), Accelerated Function Unit (AFU) and Private Features,
+as illustrated below:
+ Header Header Header Header
+ +----------+ +-->+----------+ +-->+----------+ +-->+----------+
+ | Type | | | Type | | | Type | | | Type |
+ | FIU | | | Private | | | Private | | | Private |
+ +----------+ | | Feature | | | Feature | | | Feature |
+ | Next_DFH |--+ +----------+ | +----------+ | +----------+
+ +----------+ | Next_DFH |--+ | Next_DFH |--+ | Next_DFH |--> NULL
+ | ID | +----------+ +----------+ +----------+
+ +----------+ | ID | | ID | | ID |
+ | Next_AFU |--+ +----------+ +----------+ +----------+
+ +----------+ | | Feature | | Feature | | Feature |
+ | Header | | | Register | | Register | | Register |
+ | Register | | | Set | | Set | | Set |
+ | Set | | +----------+ +----------+ +----------+
+ +----------+ | Header
+ +-->+----------+
+ | Type |
+ | AFU |
+ +----------+
+ | Next_DFH |--> NULL
+ +----------+
+ | GUID |
+ +----------+
+ | Header |
+ | Register |
+ | Set |
+ +----------+
+FPGA Interface Unit (FIU) represents a standalone functional unit for the
+interface to FPGA, e.g the FPGA Management Engine (FME) and Port (more
+descriptions on FME and Port in later sections).
+Accelerated Function Unit (AFU) represents a FPGA programmable region, and
+always connects to a FIU (e.g a Port) as its child as illustrated above.
+Private Features represent sub features of the FIU and AFU. They could be
+various function blocks with different IDs, but all private features which
+belong to the same FIU or AFU, must be linked to one list via the Next Device
+Feature Header (Next_DFH) pointer.
+Each FIU, AFU and Private Feature could implement its own functional registers.
+The functional register set for FIU and AFU, is named as Header Register Set,
+e.g FME Header Register Set, and the one for Private Feature, is named as
+Feature Register Set, e.g FME Partial Reconfiguration Feature Register Set.
+This Device Feature List provides a way of linking features together, it's
+convenient for software to locate each feature by walking through this list,
+and can be implemented in register regions of any FPGA device.
+FIU - FME (FPGA Management Engine)
+The FPGA Management Engine performs reconfiguration, and other infrastructure
+functions. Each FPGA device only has one FME.
+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 (DFL_FPGA_GET_API_VERSION)
+ Check for extensions (DFL_FPGA_CHECK_EXTENSION)
+ Program bitstream (DFL_FPGA_FME_PORT_PR)
+More functions are exposed through sysfs
+ Read bitstream ID (bitstream_id)
+ bitstream_id indicates version of the static FPGA region.
+ Read bitstream metadata (bitstream_metadata)
+ bitstream_metadata includes detailed information of static FPGA region,
+ e.g synthesis date and seed.
+ Read number of ports (ports_num)
+ one FPGA device may have more than 1 port, this sysfs interface indicates
+ how many ports the FPGA device has.
+A port represents the interface between the static FPGA fabric and a partially
+reconfigurable region containing an AFU. It controls the communication from SW
+to the accelerator and exposes features such as reset and debug. Each FPGA
+device may have more than 1 port, but always 1 AFU per port.
+An AFU is attached to a port FIU and exposes a fixed length 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 (DFL_FPGA_GET_API_VERSION)
+ Check for extensions (DFL_FPGA_CHECK_EXTENSION)
+ Get port info (DFL_FPGA_PORT_GET_INFO)
+*DFL_FPGA_PORT_RESET: reset the FPGA Port and its AFU. Userspace can do Port
+reset at any time, e.g during DMA or Partial Reconfiguration. But it should
+never cause any system level issue, only functional failure (e.g DMA or PR
+operation failure) and be recoverable from the failure.
+User-space applications can also mmap() accelerator MMIO regions.
+More functions are exposed through sysfs:
+ Read Accelerator GUID (afu_id)
+ afu_id indicates which PR bitstream is programmed to this AFU.
+DFL Framework Overview
+ +----------+ +--------+ +--------+ +--------+
+ | FME | | AFU | | AFU | | AFU |
+ | Module | | Module | | Module | | Module |
+ +----------+ +--------+ +--------+ +--------+
+ +-----------------------+
+ | FPGA Container Device | Device Feature List
+ | (FPGA Base Region) | Framework
+ +-----------------------+
+ +----------------------------+
+ | FPGA DFL Device Module |
+ | (e.g PCIE/Platform Device) |
+ +----------------------------+
+ +------------------------+
+ | FPGA Hardware Device |
+ +------------------------+
+DFL framework in kernel provides common interfaces to create container device
+(FPGA base region), discover feature devices and their private features from the
+given Device Feature Lists, and create platform devices for feature devices
+(e.g FME, Port and AFU) with related resources under the container device. It
+also abstracts operations for the private features and exposes common ops to
+feature device drivers.
+The FPGA DFL Device could be different hardwares, e.g PCIe device, platform
+device and etc. Its driver module is always loaded first once the device is
+created by the system. This driver plays an infrastructural role in the
+driver architecture. It locates the DFLs in the device memory, handles them
+and related resources to common interfaces from DFL framework for enumeration.
+(Please refer to drivers/fpga/dfl.c for detailed enumeration APIs).
+The FPGA Management Engine (FME) driver is a platform driver which is loaded
+automatically after FME platform device creation from the DFL device module. It
+provides the key features for FPGA management, including:
+ a) Expose static FPGA region information, e.g version and metadata.
+ Users can read related information 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 a DFL_FPGA_FME_PORT_PR ioctl from user, it invokes the
+ common interface function from FPGA Region to complete the partial
+ reconfiguration of the PR bitstream to the given port.
+Similar to 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 functions.
+After feature platform devices creation, matched platform drivers will be loaded
+automatically to handle different functionalities. Please refer to next sections
+for detailed information on functional units which have been already implemented
+under this DFL framework.
+Partial Reconfiguration
+As mentioned above, accelerators can be reconfigured through partial
+reconfiguration of a PR bitstream file. The PR bitstream file must have been
+generated for the exact static FPGA region 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 compatibility ID noted in the header of PR bitstream file against
+the compat_id exposed by the target FPGA region. This check is usually done by
+userspace before calling the reconfiguration IOCTL.
+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 DFL based 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 "dfl-port.n" or "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/dfl-fme.0
+ /sys/class/fpga_region/region0/dfl-port.0
+ /sys/class/fpga_region/region0/dfl-port.1
+ ...
+ /sys/class/fpga_region/region3/dfl-fme.1
+ /sys/class/fpga_region/region3/dfl-port.2
+ /sys/class/fpga_region/region3/dfl-port.3
+ ...
+In general, the FME/AFU sysfs interfaces are named as follows:
+ /sys/class/fpga_region/<regionX>/<dfl-fme.n>/
+ /sys/class/fpga_region/<regionX>/<dfl-port.m>/
+with 'n' consecutively numbering all FMEs and 'm' consecutively numbering all
+The device nodes used for ioctl() or mmap() can be referenced through:
+ /sys/class/fpga_region/<regionX>/<dfl-fme.n>/dev
+ /sys/class/fpga_region/<regionX>/<dfl-port.n>/dev
+Add new FIUs support
+It's possible that developers made some new function blocks (FIUs) under this
+DFL framework, then new platform device driver needs to be developed for the
+new feature dev (FIU) following the same way as existing feature dev drivers
+(e.g FME and Port/AFU platform device driver). Besides that, it requires
+modification on DFL framework enumeration code too, for new FIU type detection
+and related platform devices creation.
+Add new private features support
+In some cases, we may need to add some new private features to existing FIUs
+(e.g FME or Port). Developers don't need to touch enumeration code in DFL
+framework, as each private feature will be parsed automatically, and related
+mmio resources can be found under FIU platform device created by DFL framework.
+Developer only needs to provide a sub feature driver with matched feature id.
+FME Partial Reconfiguration Sub Feature driver (see drivers/fpga/dfl-fme-pr.c)
+could be a reference.
+Open discussion
+FME driver exports one ioctl (DFL_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.
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