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diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst new file mode 100644 index 000000000000..2f125abd777f --- /dev/null +++ b/Documentation/fpga/dfl.rst @@ -0,0 +1,291 @@ +================================================= +FPGA Device Feature List (DFL) Framework Overview +================================================= + +Authors: + +- Enno Luebbers <enno.luebbers@intel.com> +- Xiao Guangrong <guangrong.xiao@linux.intel.com> +- Wu Hao <hao.wu@intel.com> + +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 +implement 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 +(/sys/class/fpga_region/regionX/dfl-fme.n/): + + 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 one port, this sysfs interface indicates + how many ports the FPGA device has. + + +FIU - PORT +========== +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 one port, but always one AFU per port. + + +AFU +=== +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) +- Get MMIO region info (DFL_FPGA_PORT_GET_REGION_INFO) +- Map DMA buffer (DFL_FPGA_PORT_DMA_MAP) +- Unmap DMA buffer (DFL_FPGA_PORT_DMA_UNMAP) +- Reset AFU (DFL_FPGA_PORT_RESET) + +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: +(/sys/class/fpga_region/<regionX>/<dfl-port.m>/): + + 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 +ports. + +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. |