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1 | ================================================= |
2 | FPGA Device Feature List (DFL) Framework Overview | |
3 | ================================================= | |
4 | ||
5 | Authors: | |
6 | ||
7 | - Enno Luebbers <enno.luebbers@intel.com> | |
8 | - Xiao Guangrong <guangrong.xiao@linux.intel.com> | |
9 | - Wu Hao <hao.wu@intel.com> | |
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10 | |
11 | The Device Feature List (DFL) FPGA framework (and drivers according to this | |
12 | this framework) hides the very details of low layer hardwares and provides | |
13 | unified interfaces to userspace. Applications could use these interfaces to | |
14 | configure, enumerate, open and access FPGA accelerators on platforms which | |
15 | implement the DFL in the device memory. Besides this, the DFL framework | |
16 | enables system level management functions such as FPGA reconfiguration. | |
17 | ||
18 | ||
19 | Device Feature List (DFL) Overview | |
20 | ================================== | |
21 | Device Feature List (DFL) defines a linked list of feature headers within the | |
22 | device MMIO space to provide an extensible way of adding features. Software can | |
23 | walk through these predefined data structures to enumerate FPGA features: | |
24 | FPGA Interface Unit (FIU), Accelerated Function Unit (AFU) and Private Features, | |
c220a1fa | 25 | as illustrated below:: |
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26 | |
27 | Header Header Header Header | |
28 | +----------+ +-->+----------+ +-->+----------+ +-->+----------+ | |
29 | | Type | | | Type | | | Type | | | Type | | |
30 | | FIU | | | Private | | | Private | | | Private | | |
31 | +----------+ | | Feature | | | Feature | | | Feature | | |
32 | | Next_DFH |--+ +----------+ | +----------+ | +----------+ | |
33 | +----------+ | Next_DFH |--+ | Next_DFH |--+ | Next_DFH |--> NULL | |
34 | | ID | +----------+ +----------+ +----------+ | |
35 | +----------+ | ID | | ID | | ID | | |
36 | | Next_AFU |--+ +----------+ +----------+ +----------+ | |
37 | +----------+ | | Feature | | Feature | | Feature | | |
38 | | Header | | | Register | | Register | | Register | | |
39 | | Register | | | Set | | Set | | Set | | |
40 | | Set | | +----------+ +----------+ +----------+ | |
41 | +----------+ | Header | |
42 | +-->+----------+ | |
43 | | Type | | |
44 | | AFU | | |
45 | +----------+ | |
46 | | Next_DFH |--> NULL | |
47 | +----------+ | |
48 | | GUID | | |
49 | +----------+ | |
50 | | Header | | |
51 | | Register | | |
52 | | Set | | |
53 | +----------+ | |
54 | ||
55 | FPGA Interface Unit (FIU) represents a standalone functional unit for the | |
56 | interface to FPGA, e.g. the FPGA Management Engine (FME) and Port (more | |
57 | descriptions on FME and Port in later sections). | |
58 | ||
59 | Accelerated Function Unit (AFU) represents a FPGA programmable region and | |
60 | always connects to a FIU (e.g. a Port) as its child as illustrated above. | |
61 | ||
62 | Private Features represent sub features of the FIU and AFU. They could be | |
63 | various function blocks with different IDs, but all private features which | |
64 | belong to the same FIU or AFU, must be linked to one list via the Next Device | |
65 | Feature Header (Next_DFH) pointer. | |
66 | ||
67 | Each FIU, AFU and Private Feature could implement its own functional registers. | |
68 | The functional register set for FIU and AFU, is named as Header Register Set, | |
69 | e.g. FME Header Register Set, and the one for Private Feature, is named as | |
70 | Feature Register Set, e.g. FME Partial Reconfiguration Feature Register Set. | |
71 | ||
72 | This Device Feature List provides a way of linking features together, it's | |
73 | convenient for software to locate each feature by walking through this list, | |
74 | and can be implemented in register regions of any FPGA device. | |
75 | ||
76 | ||
77 | FIU - FME (FPGA Management Engine) | |
78 | ================================== | |
79 | The FPGA Management Engine performs reconfiguration and other infrastructure | |
80 | functions. Each FPGA device only has one FME. | |
81 | ||
82 | User-space applications can acquire exclusive access to the FME using open(), | |
83 | and release it using close(). | |
84 | ||
85 | The following functions are exposed through ioctls: | |
86 | ||
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87 | - Get driver API version (DFL_FPGA_GET_API_VERSION) |
88 | - Check for extensions (DFL_FPGA_CHECK_EXTENSION) | |
89 | - Program bitstream (DFL_FPGA_FME_PORT_PR) | |
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90 | - Assign port to PF (DFL_FPGA_FME_PORT_ASSIGN) |
91 | - Release port from PF (DFL_FPGA_FME_PORT_RELEASE) | |
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92 | |
93 | More functions are exposed through sysfs | |
94 | (/sys/class/fpga_region/regionX/dfl-fme.n/): | |
95 | ||
96 | Read bitstream ID (bitstream_id) | |
97 | bitstream_id indicates version of the static FPGA region. | |
98 | ||
99 | Read bitstream metadata (bitstream_metadata) | |
100 | bitstream_metadata includes detailed information of static FPGA region, | |
101 | e.g. synthesis date and seed. | |
102 | ||
103 | Read number of ports (ports_num) | |
104 | one FPGA device may have more than one port, this sysfs interface indicates | |
105 | how many ports the FPGA device has. | |
106 | ||
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107 | Global error reporting management (errors/) |
108 | error reporting sysfs interfaces allow user to read errors detected by the | |
109 | hardware, and clear the logged errors. | |
110 | ||
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111 | |
112 | FIU - PORT | |
113 | ========== | |
114 | A port represents the interface between the static FPGA fabric and a partially | |
115 | reconfigurable region containing an AFU. It controls the communication from SW | |
116 | to the accelerator and exposes features such as reset and debug. Each FPGA | |
117 | device may have more than one port, but always one AFU per port. | |
118 | ||
119 | ||
120 | AFU | |
121 | === | |
122 | An AFU is attached to a port FIU and exposes a fixed length MMIO region to be | |
123 | used for accelerator-specific control registers. | |
124 | ||
125 | User-space applications can acquire exclusive access to an AFU attached to a | |
126 | port by using open() on the port device node and release it using close(). | |
127 | ||
128 | The following functions are exposed through ioctls: | |
129 | ||
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130 | - Get driver API version (DFL_FPGA_GET_API_VERSION) |
131 | - Check for extensions (DFL_FPGA_CHECK_EXTENSION) | |
132 | - Get port info (DFL_FPGA_PORT_GET_INFO) | |
133 | - Get MMIO region info (DFL_FPGA_PORT_GET_REGION_INFO) | |
134 | - Map DMA buffer (DFL_FPGA_PORT_DMA_MAP) | |
135 | - Unmap DMA buffer (DFL_FPGA_PORT_DMA_UNMAP) | |
136 | - Reset AFU (DFL_FPGA_PORT_RESET) | |
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138 | DFL_FPGA_PORT_RESET: |
139 | reset the FPGA Port and its AFU. Userspace can do Port | |
140 | reset at any time, e.g. during DMA or Partial Reconfiguration. But it should | |
141 | never cause any system level issue, only functional failure (e.g. DMA or PR | |
142 | operation failure) and be recoverable from the failure. | |
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143 | |
144 | User-space applications can also mmap() accelerator MMIO regions. | |
145 | ||
146 | More functions are exposed through sysfs: | |
147 | (/sys/class/fpga_region/<regionX>/<dfl-port.m>/): | |
148 | ||
149 | Read Accelerator GUID (afu_id) | |
150 | afu_id indicates which PR bitstream is programmed to this AFU. | |
151 | ||
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152 | Error reporting (errors/) |
153 | error reporting sysfs interfaces allow user to read port/afu errors | |
154 | detected by the hardware, and clear the logged errors. | |
155 | ||
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156 | |
157 | DFL Framework Overview | |
158 | ====================== | |
159 | ||
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160 | :: |
161 | ||
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162 | +----------+ +--------+ +--------+ +--------+ |
163 | | FME | | AFU | | AFU | | AFU | | |
164 | | Module | | Module | | Module | | Module | | |
165 | +----------+ +--------+ +--------+ +--------+ | |
166 | +-----------------------+ | |
167 | | FPGA Container Device | Device Feature List | |
168 | | (FPGA Base Region) | Framework | |
169 | +-----------------------+ | |
c220a1fa | 170 | ------------------------------------------------------------------ |
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171 | +----------------------------+ |
172 | | FPGA DFL Device Module | | |
173 | | (e.g. PCIE/Platform Device)| | |
174 | +----------------------------+ | |
175 | +------------------------+ | |
176 | | FPGA Hardware Device | | |
177 | +------------------------+ | |
178 | ||
179 | DFL framework in kernel provides common interfaces to create container device | |
180 | (FPGA base region), discover feature devices and their private features from the | |
181 | given Device Feature Lists and create platform devices for feature devices | |
182 | (e.g. FME, Port and AFU) with related resources under the container device. It | |
183 | also abstracts operations for the private features and exposes common ops to | |
184 | feature device drivers. | |
185 | ||
186 | The FPGA DFL Device could be different hardwares, e.g. PCIe device, platform | |
187 | device and etc. Its driver module is always loaded first once the device is | |
188 | created by the system. This driver plays an infrastructural role in the | |
189 | driver architecture. It locates the DFLs in the device memory, handles them | |
190 | and related resources to common interfaces from DFL framework for enumeration. | |
191 | (Please refer to drivers/fpga/dfl.c for detailed enumeration APIs). | |
192 | ||
193 | The FPGA Management Engine (FME) driver is a platform driver which is loaded | |
194 | automatically after FME platform device creation from the DFL device module. It | |
195 | provides the key features for FPGA management, including: | |
196 | ||
197 | a) Expose static FPGA region information, e.g. version and metadata. | |
198 | Users can read related information via sysfs interfaces exposed | |
199 | by FME driver. | |
200 | ||
201 | b) Partial Reconfiguration. The FME driver creates FPGA manager, FPGA | |
202 | bridges and FPGA regions during PR sub feature initialization. Once | |
203 | it receives a DFL_FPGA_FME_PORT_PR ioctl from user, it invokes the | |
204 | common interface function from FPGA Region to complete the partial | |
205 | reconfiguration of the PR bitstream to the given port. | |
206 | ||
207 | Similar to the FME driver, the FPGA Accelerated Function Unit (AFU) driver is | |
208 | probed once the AFU platform device is created. The main function of this module | |
209 | is to provide an interface for userspace applications to access the individual | |
210 | accelerators, including basic reset control on port, AFU MMIO region export, dma | |
211 | buffer mapping service functions. | |
212 | ||
213 | After feature platform devices creation, matched platform drivers will be loaded | |
214 | automatically to handle different functionalities. Please refer to next sections | |
215 | for detailed information on functional units which have been already implemented | |
216 | under this DFL framework. | |
217 | ||
218 | ||
219 | Partial Reconfiguration | |
220 | ======================= | |
221 | As mentioned above, accelerators can be reconfigured through partial | |
222 | reconfiguration of a PR bitstream file. The PR bitstream file must have been | |
223 | generated for the exact static FPGA region and targeted reconfigurable region | |
224 | (port) of the FPGA, otherwise, the reconfiguration operation will fail and | |
225 | possibly cause system instability. This compatibility can be checked by | |
226 | comparing the compatibility ID noted in the header of PR bitstream file against | |
227 | the compat_id exposed by the target FPGA region. This check is usually done by | |
228 | userspace before calling the reconfiguration IOCTL. | |
229 | ||
230 | ||
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231 | FPGA virtualization - PCIe SRIOV |
232 | ================================ | |
233 | This section describes the virtualization support on DFL based FPGA device to | |
234 | enable accessing an accelerator from applications running in a virtual machine | |
235 | (VM). This section only describes the PCIe based FPGA device with SRIOV support. | |
236 | ||
237 | Features supported by the particular FPGA device are exposed through Device | |
238 | Feature Lists, as illustrated below: | |
239 | ||
240 | :: | |
241 | ||
242 | +-------------------------------+ +-------------+ | |
243 | | PF | | VF | | |
244 | +-------------------------------+ +-------------+ | |
245 | ^ ^ ^ ^ | |
246 | | | | | | |
247 | +-----|------------|---------|--------------|-------+ | |
248 | | | | | | | | |
249 | | +-----+ +-------+ +-------+ +-------+ | | |
250 | | | FME | | Port0 | | Port1 | | Port2 | | | |
251 | | +-----+ +-------+ +-------+ +-------+ | | |
252 | | ^ ^ ^ | | |
253 | | | | | | | |
254 | | +-------+ +------+ +-------+ | | |
255 | | | AFU | | AFU | | AFU | | | |
256 | | +-------+ +------+ +-------+ | | |
257 | | | | |
258 | | DFL based FPGA PCIe Device | | |
259 | +---------------------------------------------------+ | |
260 | ||
261 | FME is always accessed through the physical function (PF). | |
262 | ||
263 | Ports (and related AFUs) are accessed via PF by default, but could be exposed | |
264 | through virtual function (VF) devices via PCIe SRIOV. Each VF only contains | |
265 | 1 Port and 1 AFU for isolation. Users could assign individual VFs (accelerators) | |
266 | created via PCIe SRIOV interface, to virtual machines. | |
267 | ||
268 | The driver organization in virtualization case is illustrated below: | |
269 | :: | |
270 | ||
271 | +-------++------++------+ | | |
272 | | FME || FME || FME | | | |
273 | | FPGA || FPGA || FPGA | | | |
274 | |Manager||Bridge||Region| | | |
275 | +-------++------++------+ | | |
276 | +-----------------------+ +--------+ | +--------+ | |
277 | | FME | | AFU | | | AFU | | |
278 | | Module | | Module | | | Module | | |
279 | +-----------------------+ +--------+ | +--------+ | |
280 | +-----------------------+ | +-----------------------+ | |
281 | | FPGA Container Device | | | FPGA Container Device | | |
282 | | (FPGA Base Region) | | | (FPGA Base Region) | | |
283 | +-----------------------+ | +-----------------------+ | |
284 | +------------------+ | +------------------+ | |
285 | | FPGA PCIE Module | | Virtual | FPGA PCIE Module | | |
286 | +------------------+ Host | Machine +------------------+ | |
287 | -------------------------------------- | ------------------------------ | |
288 | +---------------+ | +---------------+ | |
289 | | PCI PF Device | | | PCI VF Device | | |
290 | +---------------+ | +---------------+ | |
291 | ||
292 | FPGA PCIe device driver is always loaded first once a FPGA PCIe PF or VF device | |
293 | is detected. It: | |
294 | ||
295 | * Finishes enumeration on both FPGA PCIe PF and VF device using common | |
296 | interfaces from DFL framework. | |
297 | * Supports SRIOV. | |
298 | ||
299 | The FME device driver plays a management role in this driver architecture, it | |
300 | provides ioctls to release Port from PF and assign Port to PF. After release | |
301 | a port from PF, then it's safe to expose this port through a VF via PCIe SRIOV | |
302 | sysfs interface. | |
303 | ||
304 | To enable accessing an accelerator from applications running in a VM, the | |
305 | respective AFU's port needs to be assigned to a VF using the following steps: | |
306 | ||
307 | #. The PF owns all AFU ports by default. Any port that needs to be | |
308 | reassigned to a VF must first be released through the | |
309 | DFL_FPGA_FME_PORT_RELEASE ioctl on the FME device. | |
310 | ||
311 | #. Once N ports are released from PF, then user can use command below | |
312 | to enable SRIOV and VFs. Each VF owns only one Port with AFU. | |
313 | ||
314 | :: | |
315 | ||
316 | echo N > $PCI_DEVICE_PATH/sriov_numvfs | |
317 | ||
318 | #. Pass through the VFs to VMs | |
319 | ||
320 | #. The AFU under VF is accessible from applications in VM (using the | |
321 | same driver inside the VF). | |
322 | ||
323 | Note that an FME can't be assigned to a VF, thus PR and other management | |
324 | functions are only available via the PF. | |
325 | ||
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326 | Device enumeration |
327 | ================== | |
328 | This section introduces how applications enumerate the fpga device from | |
329 | the sysfs hierarchy under /sys/class/fpga_region. | |
330 | ||
331 | In the example below, two DFL based FPGA devices are installed in the host. Each | |
332 | fpga device has one FME and two ports (AFUs). | |
333 | ||
c220a1fa | 334 | FPGA regions are created under /sys/class/fpga_region/:: |
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335 | |
336 | /sys/class/fpga_region/region0 | |
337 | /sys/class/fpga_region/region1 | |
338 | /sys/class/fpga_region/region2 | |
339 | ... | |
340 | ||
341 | Application needs to search each regionX folder, if feature device is found, | |
342 | (e.g. "dfl-port.n" or "dfl-fme.m" is found), then it's the base | |
343 | fpga region which represents the FPGA device. | |
344 | ||
c220a1fa | 345 | Each base region has one FME and two ports (AFUs) as child devices:: |
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346 | |
347 | /sys/class/fpga_region/region0/dfl-fme.0 | |
348 | /sys/class/fpga_region/region0/dfl-port.0 | |
349 | /sys/class/fpga_region/region0/dfl-port.1 | |
350 | ... | |
351 | ||
352 | /sys/class/fpga_region/region3/dfl-fme.1 | |
353 | /sys/class/fpga_region/region3/dfl-port.2 | |
354 | /sys/class/fpga_region/region3/dfl-port.3 | |
355 | ... | |
356 | ||
c220a1fa | 357 | In general, the FME/AFU sysfs interfaces are named as follows:: |
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358 | |
359 | /sys/class/fpga_region/<regionX>/<dfl-fme.n>/ | |
360 | /sys/class/fpga_region/<regionX>/<dfl-port.m>/ | |
361 | ||
362 | with 'n' consecutively numbering all FMEs and 'm' consecutively numbering all | |
363 | ports. | |
364 | ||
c220a1fa | 365 | The device nodes used for ioctl() or mmap() can be referenced through:: |
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366 | |
367 | /sys/class/fpga_region/<regionX>/<dfl-fme.n>/dev | |
368 | /sys/class/fpga_region/<regionX>/<dfl-port.n>/dev | |
369 | ||
370 | ||
371 | Add new FIUs support | |
372 | ==================== | |
373 | It's possible that developers made some new function blocks (FIUs) under this | |
374 | DFL framework, then new platform device driver needs to be developed for the | |
375 | new feature dev (FIU) following the same way as existing feature dev drivers | |
376 | (e.g. FME and Port/AFU platform device driver). Besides that, it requires | |
377 | modification on DFL framework enumeration code too, for new FIU type detection | |
378 | and related platform devices creation. | |
379 | ||
380 | ||
381 | Add new private features support | |
382 | ================================ | |
383 | In some cases, we may need to add some new private features to existing FIUs | |
384 | (e.g. FME or Port). Developers don't need to touch enumeration code in DFL | |
385 | framework, as each private feature will be parsed automatically and related | |
386 | mmio resources can be found under FIU platform device created by DFL framework. | |
387 | Developer only needs to provide a sub feature driver with matched feature id. | |
388 | FME Partial Reconfiguration Sub Feature driver (see drivers/fpga/dfl-fme-pr.c) | |
389 | could be a reference. | |
390 | ||
391 | ||
392 | Open discussion | |
393 | =============== | |
394 | FME driver exports one ioctl (DFL_FPGA_FME_PORT_PR) for partial reconfiguration | |
395 | to user now. In the future, if unified user interfaces for reconfiguration are | |
396 | added, FME driver should switch to them from ioctl interface. |