| ================================================= |
| 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) |
| - Assign port to PF (DFL_FPGA_FME_PORT_ASSIGN) |
| - Release port from PF (DFL_FPGA_FME_PORT_RELEASE) |
| |
| 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. |
| |
| Global error reporting management (errors/) |
| error reporting sysfs interfaces allow user to read errors detected by the |
| hardware, and clear the logged errors. |
| |
| Power management (dfl_fme_power hwmon) |
| power management hwmon sysfs interfaces allow user to read power management |
| information (power consumption, thresholds, threshold status, limits, etc.) |
| and configure power thresholds for different throttling levels. |
| |
| Thermal management (dfl_fme_thermal hwmon) |
| thermal management hwmon sysfs interfaces allow user to read thermal |
| management information (current temperature, thresholds, threshold status, |
| etc.). |
| |
| Performance reporting |
| performance counters are exposed through perf PMU APIs. Standard perf tool |
| can be used to monitor all available perf events. Please see performance |
| counter section below for more detailed information. |
| |
| |
| 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. |
| |
| Error reporting (errors/) |
| error reporting sysfs interfaces allow user to read port/afu errors |
| detected by the hardware, and clear the logged errors. |
| |
| |
| 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. |
| |
| |
| FPGA virtualization - PCIe SRIOV |
| ================================ |
| This section describes the virtualization support on DFL based FPGA device to |
| enable accessing an accelerator from applications running in a virtual machine |
| (VM). This section only describes the PCIe based FPGA device with SRIOV support. |
| |
| Features supported by the particular FPGA device are exposed through Device |
| Feature Lists, as illustrated below: |
| |
| :: |
| |
| +-------------------------------+ +-------------+ |
| | PF | | VF | |
| +-------------------------------+ +-------------+ |
| ^ ^ ^ ^ |
| | | | | |
| +-----|------------|---------|--------------|-------+ |
| | | | | | | |
| | +-----+ +-------+ +-------+ +-------+ | |
| | | FME | | Port0 | | Port1 | | Port2 | | |
| | +-----+ +-------+ +-------+ +-------+ | |
| | ^ ^ ^ | |
| | | | | | |
| | +-------+ +------+ +-------+ | |
| | | AFU | | AFU | | AFU | | |
| | +-------+ +------+ +-------+ | |
| | | |
| | DFL based FPGA PCIe Device | |
| +---------------------------------------------------+ |
| |
| FME is always accessed through the physical function (PF). |
| |
| Ports (and related AFUs) are accessed via PF by default, but could be exposed |
| through virtual function (VF) devices via PCIe SRIOV. Each VF only contains |
| 1 Port and 1 AFU for isolation. Users could assign individual VFs (accelerators) |
| created via PCIe SRIOV interface, to virtual machines. |
| |
| The driver organization in virtualization case is illustrated below: |
| :: |
| |
| +-------++------++------+ | |
| | 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 | |
| +---------------+ | +---------------+ |
| |
| FPGA PCIe device driver is always loaded first once a FPGA PCIe PF or VF device |
| is detected. It: |
| |
| * Finishes enumeration on both FPGA PCIe PF and VF device using common |
| interfaces from DFL framework. |
| * Supports SRIOV. |
| |
| The FME device driver plays a management role in this driver architecture, it |
| provides ioctls to release Port from PF and assign Port to PF. After release |
| a port from PF, then it's safe to expose this port through a VF via PCIe SRIOV |
| sysfs interface. |
| |
| 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: |
| |
| #. The PF owns all AFU ports by default. Any port that needs to be |
| reassigned to a VF must first be released through the |
| DFL_FPGA_FME_PORT_RELEASE ioctl on the FME device. |
| |
| #. 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 |
| |
| #. Pass through the VFs to VMs |
| |
| #. 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. |
| |
| 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 |
| |
| |
| Performance Counters |
| ==================== |
| Performance reporting is one private feature implemented in FME. It could |
| supports several independent, system-wide, device counter sets in hardware to |
| monitor and count for performance events, including "basic", "cache", "fabric", |
| "vtd" and "vtd_sip" counters. Users could use standard perf tool to monitor |
| FPGA cache hit/miss rate, transaction number, interface clock counter of AFU |
| and other FPGA performance events. |
| |
| Different FPGA devices may have different counter sets, depending on hardware |
| implementation. E.g., some discrete FPGA cards don't have any cache. User could |
| use "perf list" to check which perf events are supported by target hardware. |
| |
| In order to allow user to use standard perf API to access these performance |
| counters, driver creates a perf PMU, and related sysfs interfaces in |
| /sys/bus/event_source/devices/dfl_fme* to describe available perf events and |
| configuration options. |
| |
| The "format" directory describes the format of the config field of struct |
| perf_event_attr. There are 3 bitfields for config: "evtype" defines which type |
| the perf event belongs to; "event" is the identity of the event within its |
| category; "portid" is introduced to decide counters set to monitor on FPGA |
| overall data or a specific port. |
| |
| The "events" directory describes the configuration templates for all available |
| events which can be used with perf tool directly. For example, fab_mmio_read |
| has the configuration "event=0x06,evtype=0x02,portid=0xff", which shows this |
| event belongs to fabric type (0x02), the local event id is 0x06 and it is for |
| overall monitoring (portid=0xff). |
| |
| Example usage of perf:: |
| |
| $# perf list |grep dfl_fme |
| |
| dfl_fme0/fab_mmio_read/ [Kernel PMU event] |
| <...> |
| dfl_fme0/fab_port_mmio_read,portid=?/ [Kernel PMU event] |
| <...> |
| |
| $# perf stat -a -e dfl_fme0/fab_mmio_read/ <command> |
| or |
| $# perf stat -a -e dfl_fme0/event=0x06,evtype=0x02,portid=0xff/ <command> |
| or |
| $# perf stat -a -e dfl_fme0/config=0xff2006/ <command> |
| |
| Another example, fab_port_mmio_read monitors mmio read of a specific port. So |
| its configuration template is "event=0x06,evtype=0x01,portid=?". The portid |
| should be explicitly set. |
| |
| Its usage of perf:: |
| |
| $# perf stat -a -e dfl_fme0/fab_port_mmio_read,portid=0x0/ <command> |
| or |
| $# perf stat -a -e dfl_fme0/event=0x06,evtype=0x02,portid=0x0/ <command> |
| or |
| $# perf stat -a -e dfl_fme0/config=0x2006/ <command> |
| |
| Please note for fabric counters, overall perf events (fab_*) and port perf |
| events (fab_port_*) actually share one set of counters in hardware, so it can't |
| monitor both at the same time. If this set of counters is configured to monitor |
| overall data, then per port perf data is not supported. See below example:: |
| |
| $# perf stat -e dfl_fme0/fab_mmio_read/,dfl_fme0/fab_port_mmio_write,\ |
| portid=0/ sleep 1 |
| |
| Performance counter stats for 'system wide': |
| |
| 3 dfl_fme0/fab_mmio_read/ |
| <not supported> dfl_fme0/fab_port_mmio_write,portid=0x0/ |
| |
| 1.001750904 seconds time elapsed |
| |
| The driver also provides a "cpumask" sysfs attribute, which contains only one |
| CPU id used to access these perf events. Counting on multiple CPU is not allowed |
| since they are system-wide counters on FPGA device. |
| |
| The current driver does not support sampling. So "perf record" is unsupported. |
| |
| |
| 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. |
