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