xref: /openbmc/linux/Documentation/fpga/dfl.rst (revision 5b448065) 
1=================================================
2FPGA Device Feature List (DFL) Framework Overview
3=================================================
4
5Authors:
6
7- Enno Luebbers <enno.luebbers@intel.com>
8- Xiao Guangrong <guangrong.xiao@linux.intel.com>
9- Wu Hao <hao.wu@intel.com>
10- Xu Yilun <yilun.xu@intel.com>
11
12The Device Feature List (DFL) FPGA framework (and drivers according to
13this framework) hides the very details of low layer hardwares and provides
14unified interfaces to userspace. Applications could use these interfaces to
15configure, enumerate, open and access FPGA accelerators on platforms which
16implement the DFL in the device memory. Besides this, the DFL framework
17enables system level management functions such as FPGA reconfiguration.
18
19
20Device Feature List (DFL) Overview
21==================================
22Device Feature List (DFL) defines a linked list of feature headers within the
23device MMIO space to provide an extensible way of adding features. Software can
24walk through these predefined data structures to enumerate FPGA features:
25FPGA Interface Unit (FIU), Accelerated Function Unit (AFU) and Private Features,
26as illustrated below::
27
28    Header            Header            Header            Header
29 +----------+  +-->+----------+  +-->+----------+  +-->+----------+
30 |   Type   |  |   |  Type    |  |   |  Type    |  |   |  Type    |
31 |   FIU    |  |   | Private  |  |   | Private  |  |   | Private  |
32 +----------+  |   | Feature  |  |   | Feature  |  |   | Feature  |
33 | Next_DFH |--+   +----------+  |   +----------+  |   +----------+
34 +----------+      | Next_DFH |--+   | Next_DFH |--+   | Next_DFH |--> NULL
35 |    ID    |      +----------+      +----------+      +----------+
36 +----------+      |    ID    |      |    ID    |      |    ID    |
37 | Next_AFU |--+   +----------+      +----------+      +----------+
38 +----------+  |   | Feature  |      | Feature  |      | Feature  |
39 |  Header  |  |   | Register |      | Register |      | Register |
40 | Register |  |   |   Set    |      |   Set    |      |   Set    |
41 |   Set    |  |   +----------+      +----------+      +----------+
42 +----------+  |      Header
43               +-->+----------+
44                   |   Type   |
45                   |   AFU    |
46                   +----------+
47                   | Next_DFH |--> NULL
48                   +----------+
49                   |   GUID   |
50                   +----------+
51                   |  Header  |
52                   | Register |
53                   |   Set    |
54                   +----------+
55
56FPGA Interface Unit (FIU) represents a standalone functional unit for the
57interface to FPGA, e.g. the FPGA Management Engine (FME) and Port (more
58descriptions on FME and Port in later sections).
59
60Accelerated Function Unit (AFU) represents a FPGA programmable region and
61always connects to a FIU (e.g. a Port) as its child as illustrated above.
62
63Private Features represent sub features of the FIU and AFU. They could be
64various function blocks with different IDs, but all private features which
65belong to the same FIU or AFU, must be linked to one list via the Next Device
66Feature Header (Next_DFH) pointer.
67
68Each FIU, AFU and Private Feature could implement its own functional registers.
69The functional register set for FIU and AFU, is named as Header Register Set,
70e.g. FME Header Register Set, and the one for Private Feature, is named as
71Feature Register Set, e.g. FME Partial Reconfiguration Feature Register Set.
72
73This Device Feature List provides a way of linking features together, it's
74convenient for software to locate each feature by walking through this list,
75and can be implemented in register regions of any FPGA device.
76
77
78FIU - FME (FPGA Management Engine)
79==================================
80The FPGA Management Engine performs reconfiguration and other infrastructure
81functions. Each FPGA device only has one FME.
82
83User-space applications can acquire exclusive access to the FME using open(),
84and release it using close().
85
86The following functions are exposed through ioctls:
87
88- Get driver API version (DFL_FPGA_GET_API_VERSION)
89- Check for extensions (DFL_FPGA_CHECK_EXTENSION)
90- Program bitstream (DFL_FPGA_FME_PORT_PR)
91- Assign port to PF (DFL_FPGA_FME_PORT_ASSIGN)
92- Release port from PF (DFL_FPGA_FME_PORT_RELEASE)
93- Get number of irqs of FME global error (DFL_FPGA_FME_ERR_GET_IRQ_NUM)
94- Set interrupt trigger for FME error (DFL_FPGA_FME_ERR_SET_IRQ)
95
96More functions are exposed through sysfs
97(/sys/class/fpga_region/regionX/dfl-fme.n/):
98
99 Read bitstream ID (bitstream_id)
100     bitstream_id indicates version of the static FPGA region.
101
102 Read bitstream metadata (bitstream_metadata)
103     bitstream_metadata includes detailed information of static FPGA region,
104     e.g. synthesis date and seed.
105
106 Read number of ports (ports_num)
107     one FPGA device may have more than one port, this sysfs interface indicates
108     how many ports the FPGA device has.
109
110 Global error reporting management (errors/)
111     error reporting sysfs interfaces allow user to read errors detected by the
112     hardware, and clear the logged errors.
113
114 Power management (dfl_fme_power hwmon)
115     power management hwmon sysfs interfaces allow user to read power management
116     information (power consumption, thresholds, threshold status, limits, etc.)
117     and configure power thresholds for different throttling levels.
118
119 Thermal management (dfl_fme_thermal hwmon)
120     thermal management hwmon sysfs interfaces allow user to read thermal
121     management information (current temperature, thresholds, threshold status,
122     etc.).
123
124 Performance reporting
125     performance counters are exposed through perf PMU APIs. Standard perf tool
126     can be used to monitor all available perf events. Please see performance
127     counter section below for more detailed information.
128
129
130FIU - PORT
131==========
132A port represents the interface between the static FPGA fabric and a partially
133reconfigurable region containing an AFU. It controls the communication from SW
134to the accelerator and exposes features such as reset and debug. Each FPGA
135device may have more than one port, but always one AFU per port.
136
137
138AFU
139===
140An AFU is attached to a port FIU and exposes a fixed length MMIO region to be
141used for accelerator-specific control registers.
142
143User-space applications can acquire exclusive access to an AFU attached to a
144port by using open() on the port device node and release it using close().
145
146The following functions are exposed through ioctls:
147
148- Get driver API version (DFL_FPGA_GET_API_VERSION)
149- Check for extensions (DFL_FPGA_CHECK_EXTENSION)
150- Get port info (DFL_FPGA_PORT_GET_INFO)
151- Get MMIO region info (DFL_FPGA_PORT_GET_REGION_INFO)
152- Map DMA buffer (DFL_FPGA_PORT_DMA_MAP)
153- Unmap DMA buffer (DFL_FPGA_PORT_DMA_UNMAP)
154- Reset AFU (DFL_FPGA_PORT_RESET)
155- Get number of irqs of port error (DFL_FPGA_PORT_ERR_GET_IRQ_NUM)
156- Set interrupt trigger for port error (DFL_FPGA_PORT_ERR_SET_IRQ)
157- Get number of irqs of UINT (DFL_FPGA_PORT_UINT_GET_IRQ_NUM)
158- Set interrupt trigger for UINT (DFL_FPGA_PORT_UINT_SET_IRQ)
159
160DFL_FPGA_PORT_RESET:
161  reset the FPGA Port and its AFU. Userspace can do Port
162  reset at any time, e.g. during DMA or Partial Reconfiguration. But it should
163  never cause any system level issue, only functional failure (e.g. DMA or PR
164  operation failure) and be recoverable from the failure.
165
166User-space applications can also mmap() accelerator MMIO regions.
167
168More functions are exposed through sysfs:
169(/sys/class/fpga_region/<regionX>/<dfl-port.m>/):
170
171 Read Accelerator GUID (afu_id)
172     afu_id indicates which PR bitstream is programmed to this AFU.
173
174 Error reporting (errors/)
175     error reporting sysfs interfaces allow user to read port/afu errors
176     detected by the hardware, and clear the logged errors.
177
178
179DFL Framework Overview
180======================
181
182::
183
184         +----------+    +--------+ +--------+ +--------+
185         |   FME    |    |  AFU   | |  AFU   | |  AFU   |
186         |  Module  |    | Module | | Module | | Module |
187         +----------+    +--------+ +--------+ +--------+
188                 +-----------------------+
189                 | FPGA Container Device |    Device Feature List
190                 |  (FPGA Base Region)   |         Framework
191                 +-----------------------+
192  ------------------------------------------------------------------
193               +----------------------------+
194               |   FPGA DFL Device Module   |
195               | (e.g. PCIE/Platform Device)|
196               +----------------------------+
197                 +------------------------+
198                 |  FPGA Hardware Device  |
199                 +------------------------+
200
201DFL framework in kernel provides common interfaces to create container device
202(FPGA base region), discover feature devices and their private features from the
203given Device Feature Lists and create platform devices for feature devices
204(e.g. FME, Port and AFU) with related resources under the container device. It
205also abstracts operations for the private features and exposes common ops to
206feature device drivers.
207
208The FPGA DFL Device could be different hardwares, e.g. PCIe device, platform
209device and etc. Its driver module is always loaded first once the device is
210created by the system. This driver plays an infrastructural role in the
211driver architecture. It locates the DFLs in the device memory, handles them
212and related resources to common interfaces from DFL framework for enumeration.
213(Please refer to drivers/fpga/dfl.c for detailed enumeration APIs).
214
215The FPGA Management Engine (FME) driver is a platform driver which is loaded
216automatically after FME platform device creation from the DFL device module. It
217provides the key features for FPGA management, including:
218
219	a) Expose static FPGA region information, e.g. version and metadata.
220	   Users can read related information via sysfs interfaces exposed
221	   by FME driver.
222
223	b) Partial Reconfiguration. The FME driver creates FPGA manager, FPGA
224	   bridges and FPGA regions during PR sub feature initialization. Once
225	   it receives a DFL_FPGA_FME_PORT_PR ioctl from user, it invokes the
226	   common interface function from FPGA Region to complete the partial
227	   reconfiguration of the PR bitstream to the given port.
228
229Similar to the FME driver, the FPGA Accelerated Function Unit (AFU) driver is
230probed once the AFU platform device is created. The main function of this module
231is to provide an interface for userspace applications to access the individual
232accelerators, including basic reset control on port, AFU MMIO region export, dma
233buffer mapping service functions.
234
235After feature platform devices creation, matched platform drivers will be loaded
236automatically to handle different functionalities. Please refer to next sections
237for detailed information on functional units which have been already implemented
238under this DFL framework.
239
240
241Partial Reconfiguration
242=======================
243As mentioned above, accelerators can be reconfigured through partial
244reconfiguration of a PR bitstream file. The PR bitstream file must have been
245generated for the exact static FPGA region and targeted reconfigurable region
246(port) of the FPGA, otherwise, the reconfiguration operation will fail and
247possibly cause system instability. This compatibility can be checked by
248comparing the compatibility ID noted in the header of PR bitstream file against
249the compat_id exposed by the target FPGA region. This check is usually done by
250userspace before calling the reconfiguration IOCTL.
251
252
253FPGA virtualization - PCIe SRIOV
254================================
255This section describes the virtualization support on DFL based FPGA device to
256enable accessing an accelerator from applications running in a virtual machine
257(VM). This section only describes the PCIe based FPGA device with SRIOV support.
258
259Features supported by the particular FPGA device are exposed through Device
260Feature Lists, as illustrated below:
261
262::
263
264    +-------------------------------+  +-------------+
265    |              PF               |  |     VF      |
266    +-------------------------------+  +-------------+
267        ^            ^         ^              ^
268        |            |         |              |
269  +-----|------------|---------|--------------|-------+
270  |     |            |         |              |       |
271  |  +-----+     +-------+ +-------+      +-------+   |
272  |  | FME |     | Port0 | | Port1 |      | Port2 |   |
273  |  +-----+     +-------+ +-------+      +-------+   |
274  |                  ^         ^              ^       |
275  |                  |         |              |       |
276  |              +-------+ +------+       +-------+   |
277  |              |  AFU  | |  AFU |       |  AFU  |   |
278  |              +-------+ +------+       +-------+   |
279  |                                                   |
280  |            DFL based FPGA PCIe Device             |
281  +---------------------------------------------------+
282
283FME is always accessed through the physical function (PF).
284
285Ports (and related AFUs) are accessed via PF by default, but could be exposed
286through virtual function (VF) devices via PCIe SRIOV. Each VF only contains
2871 Port and 1 AFU for isolation. Users could assign individual VFs (accelerators)
288created via PCIe SRIOV interface, to virtual machines.
289
290The driver organization in virtualization case is illustrated below:
291::
292
293    +-------++------++------+             |
294    | FME   || FME  || FME  |             |
295    | FPGA  || FPGA || FPGA |             |
296    |Manager||Bridge||Region|             |
297    +-------++------++------+             |
298    +-----------------------+  +--------+ |             +--------+
299    |          FME          |  |  AFU   | |             |  AFU   |
300    |         Module        |  | Module | |             | Module |
301    +-----------------------+  +--------+ |             +--------+
302          +-----------------------+       |       +-----------------------+
303          | FPGA Container Device |       |       | FPGA Container Device |
304          |  (FPGA Base Region)   |       |       |  (FPGA Base Region)   |
305          +-----------------------+       |       +-----------------------+
306            +------------------+          |         +------------------+
307            | FPGA PCIE Module |          | Virtual | FPGA PCIE Module |
308            +------------------+   Host   | Machine +------------------+
309   -------------------------------------- | ------------------------------
310             +---------------+            |          +---------------+
311             | PCI PF Device |            |          | PCI VF Device |
312             +---------------+            |          +---------------+
313
314FPGA PCIe device driver is always loaded first once a FPGA PCIe PF or VF device
315is detected. It:
316
317* Finishes enumeration on both FPGA PCIe PF and VF device using common
318  interfaces from DFL framework.
319* Supports SRIOV.
320
321The FME device driver plays a management role in this driver architecture, it
322provides ioctls to release Port from PF and assign Port to PF. After release
323a port from PF, then it's safe to expose this port through a VF via PCIe SRIOV
324sysfs interface.
325
326To enable accessing an accelerator from applications running in a VM, the
327respective AFU's port needs to be assigned to a VF using the following steps:
328
329#. The PF owns all AFU ports by default. Any port that needs to be
330   reassigned to a VF must first be released through the
331   DFL_FPGA_FME_PORT_RELEASE ioctl on the FME device.
332
333#. Once N ports are released from PF, then user can use command below
334   to enable SRIOV and VFs. Each VF owns only one Port with AFU.
335
336   ::
337
338      echo N > $PCI_DEVICE_PATH/sriov_numvfs
339
340#. Pass through the VFs to VMs
341
342#. The AFU under VF is accessible from applications in VM (using the
343   same driver inside the VF).
344
345Note that an FME can't be assigned to a VF, thus PR and other management
346functions are only available via the PF.
347
348Device enumeration
349==================
350This section introduces how applications enumerate the fpga device from
351the sysfs hierarchy under /sys/class/fpga_region.
352
353In the example below, two DFL based FPGA devices are installed in the host. Each
354fpga device has one FME and two ports (AFUs).
355
356FPGA regions are created under /sys/class/fpga_region/::
357
358	/sys/class/fpga_region/region0
359	/sys/class/fpga_region/region1
360	/sys/class/fpga_region/region2
361	...
362
363Application needs to search each regionX folder, if feature device is found,
364(e.g. "dfl-port.n" or "dfl-fme.m" is found), then it's the base
365fpga region which represents the FPGA device.
366
367Each base region has one FME and two ports (AFUs) as child devices::
368
369	/sys/class/fpga_region/region0/dfl-fme.0
370	/sys/class/fpga_region/region0/dfl-port.0
371	/sys/class/fpga_region/region0/dfl-port.1
372	...
373
374	/sys/class/fpga_region/region3/dfl-fme.1
375	/sys/class/fpga_region/region3/dfl-port.2
376	/sys/class/fpga_region/region3/dfl-port.3
377	...
378
379In general, the FME/AFU sysfs interfaces are named as follows::
380
381	/sys/class/fpga_region/<regionX>/<dfl-fme.n>/
382	/sys/class/fpga_region/<regionX>/<dfl-port.m>/
383
384with 'n' consecutively numbering all FMEs and 'm' consecutively numbering all
385ports.
386
387The device nodes used for ioctl() or mmap() can be referenced through::
388
389	/sys/class/fpga_region/<regionX>/<dfl-fme.n>/dev
390	/sys/class/fpga_region/<regionX>/<dfl-port.n>/dev
391
392
393Performance Counters
394====================
395Performance reporting is one private feature implemented in FME. It could
396supports several independent, system-wide, device counter sets in hardware to
397monitor and count for performance events, including "basic", "cache", "fabric",
398"vtd" and "vtd_sip" counters. Users could use standard perf tool to monitor
399FPGA cache hit/miss rate, transaction number, interface clock counter of AFU
400and other FPGA performance events.
401
402Different FPGA devices may have different counter sets, depending on hardware
403implementation. E.g., some discrete FPGA cards don't have any cache. User could
404use "perf list" to check which perf events are supported by target hardware.
405
406In order to allow user to use standard perf API to access these performance
407counters, driver creates a perf PMU, and related sysfs interfaces in
408/sys/bus/event_source/devices/dfl_fme* to describe available perf events and
409configuration options.
410
411The "format" directory describes the format of the config field of struct
412perf_event_attr. There are 3 bitfields for config: "evtype" defines which type
413the perf event belongs to; "event" is the identity of the event within its
414category; "portid" is introduced to decide counters set to monitor on FPGA
415overall data or a specific port.
416
417The "events" directory describes the configuration templates for all available
418events which can be used with perf tool directly. For example, fab_mmio_read
419has the configuration "event=0x06,evtype=0x02,portid=0xff", which shows this
420event belongs to fabric type (0x02), the local event id is 0x06 and it is for
421overall monitoring (portid=0xff).
422
423Example usage of perf::
424
425  $# perf list |grep dfl_fme
426
427  dfl_fme0/fab_mmio_read/                              [Kernel PMU event]
428  <...>
429  dfl_fme0/fab_port_mmio_read,portid=?/                [Kernel PMU event]
430  <...>
431
432  $# perf stat -a -e dfl_fme0/fab_mmio_read/ <command>
433  or
434  $# perf stat -a -e dfl_fme0/event=0x06,evtype=0x02,portid=0xff/ <command>
435  or
436  $# perf stat -a -e dfl_fme0/config=0xff2006/ <command>
437
438Another example, fab_port_mmio_read monitors mmio read of a specific port. So
439its configuration template is "event=0x06,evtype=0x01,portid=?". The portid
440should be explicitly set.
441
442Its usage of perf::
443
444  $# perf stat -a -e dfl_fme0/fab_port_mmio_read,portid=0x0/ <command>
445  or
446  $# perf stat -a -e dfl_fme0/event=0x06,evtype=0x02,portid=0x0/ <command>
447  or
448  $# perf stat -a -e dfl_fme0/config=0x2006/ <command>
449
450Please note for fabric counters, overall perf events (fab_*) and port perf
451events (fab_port_*) actually share one set of counters in hardware, so it can't
452monitor both at the same time. If this set of counters is configured to monitor
453overall data, then per port perf data is not supported. See below example::
454
455  $# perf stat -e dfl_fme0/fab_mmio_read/,dfl_fme0/fab_port_mmio_write,\
456                                                    portid=0/ sleep 1
457
458  Performance counter stats for 'system wide':
459
460                 3      dfl_fme0/fab_mmio_read/
461   <not supported>      dfl_fme0/fab_port_mmio_write,portid=0x0/
462
463       1.001750904 seconds time elapsed
464
465The driver also provides a "cpumask" sysfs attribute, which contains only one
466CPU id used to access these perf events. Counting on multiple CPU is not allowed
467since they are system-wide counters on FPGA device.
468
469The current driver does not support sampling. So "perf record" is unsupported.
470
471
472Interrupt support
473=================
474Some FME and AFU private features are able to generate interrupts. As mentioned
475above, users could call ioctl (DFL_FPGA_*_GET_IRQ_NUM) to know whether or how
476many interrupts are supported for this private feature. Drivers also implement
477an eventfd based interrupt handling mechanism for users to get notified when
478interrupt happens. Users could set eventfds to driver via
479ioctl (DFL_FPGA_*_SET_IRQ), and then poll/select on these eventfds waiting for
480notification.
481In Current DFL, 3 sub features (Port error, FME global error and AFU interrupt)
482support interrupts.
483
484
485Add new FIUs support
486====================
487It's possible that developers made some new function blocks (FIUs) under this
488DFL framework, then new platform device driver needs to be developed for the
489new feature dev (FIU) following the same way as existing feature dev drivers
490(e.g. FME and Port/AFU platform device driver). Besides that, it requires
491modification on DFL framework enumeration code too, for new FIU type detection
492and related platform devices creation.
493
494
495Add new private features support
496================================
497In some cases, we may need to add some new private features to existing FIUs
498(e.g. FME or Port). Developers don't need to touch enumeration code in DFL
499framework, as each private feature will be parsed automatically and related
500mmio resources can be found under FIU platform device created by DFL framework.
501Developer only needs to provide a sub feature driver with matched feature id.
502FME Partial Reconfiguration Sub Feature driver (see drivers/fpga/dfl-fme-pr.c)
503could be a reference.
504
505Location of DFLs on a PCI Device
506================================
507The original method for finding a DFL on a PCI device assumed the start of the
508first DFL to offset 0 of bar 0.  If the first node of the DFL is an FME,
509then further DFLs in the port(s) are specified in FME header registers.
510Alternatively, a PCIe vendor specific capability structure can be used to
511specify the location of all the DFLs on the device, providing flexibility
512for the type of starting node in the DFL.  Intel has reserved the
513VSEC ID of 0x43 for this purpose.  The vendor specific
514data begins with a 4 byte vendor specific register for the number of DFLs followed 4 byte
515Offset/BIR vendor specific registers for each DFL. Bits 2:0 of Offset/BIR register
516indicates the BAR, and bits 31:3 form the 8 byte aligned offset where bits 2:0 are
517zero.
518::
519
520        +----------------------------+
521        |31     Number of DFLS      0|
522        +----------------------------+
523        |31     Offset     3|2 BIR  0|
524        +----------------------------+
525                      . . .
526        +----------------------------+
527        |31     Offset     3|2 BIR  0|
528        +----------------------------+
529
530Being able to specify more than one DFL per BAR has been considered, but it
531was determined the use case did not provide value.  Specifying a single DFL
532per BAR simplifies the implementation and allows for extra error checking.
533
534
535Userspace driver support for DFL devices
536========================================
537The purpose of an FPGA is to be reprogrammed with newly developed hardware
538components. New hardware can instantiate a new private feature in the DFL, and
539then present a DFL device in the system. In some cases users may need a
540userspace driver for the DFL device:
541
542* Users may need to run some diagnostic test for their hardware.
543* Users may prototype the kernel driver in user space.
544* Some hardware is designed for specific purposes and does not fit into one of
545  the standard kernel subsystems.
546
547This requires direct access to MMIO space and interrupt handling from
548userspace. The uio_dfl module exposes the UIO device interfaces for this
549purpose.
550
551Currently the uio_dfl driver only supports the Ether Group sub feature, which
552has no irq in hardware. So the interrupt handling is not added in this driver.
553
554UIO_DFL should be selected to enable the uio_dfl module driver. To support a
555new DFL feature via UIO direct access, its feature id should be added to the
556driver's id_table.
557
558
559Open discussion
560===============
561FME driver exports one ioctl (DFL_FPGA_FME_PORT_PR) for partial reconfiguration
562to user now. In the future, if unified user interfaces for reconfiguration are
563added, FME driver should switch to them from ioctl interface.
564