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1 | Remote Processor Framework |
2 | ||
3 | 1. Introduction | |
4 | ||
5 | Modern SoCs typically have heterogeneous remote processor devices in asymmetric | |
6 | multiprocessing (AMP) configurations, which may be running different instances | |
7 | of operating system, whether it's Linux or any other flavor of real-time OS. | |
8 | ||
9 | OMAP4, for example, has dual Cortex-A9, dual Cortex-M3 and a C64x+ DSP. | |
10 | In a typical configuration, the dual cortex-A9 is running Linux in a SMP | |
11 | configuration, and each of the other three cores (two M3 cores and a DSP) | |
12 | is running its own instance of RTOS in an AMP configuration. | |
13 | ||
14 | The remoteproc framework allows different platforms/architectures to | |
15 | control (power on, load firmware, power off) those remote processors while | |
16 | abstracting the hardware differences, so the entire driver doesn't need to be | |
17 | duplicated. In addition, this framework also adds rpmsg virtio devices | |
18 | for remote processors that supports this kind of communication. This way, | |
19 | platform-specific remoteproc drivers only need to provide a few low-level | |
20 | handlers, and then all rpmsg drivers will then just work | |
21 | (for more information about the virtio-based rpmsg bus and its drivers, | |
22 | please read Documentation/rpmsg.txt). | |
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23 | Registration of other types of virtio devices is now also possible. Firmwares |
24 | just need to publish what kind of virtio devices do they support, and then | |
25 | remoteproc will add those devices. This makes it possible to reuse the | |
26 | existing virtio drivers with remote processor backends at a minimal development | |
27 | cost. | |
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28 | |
29 | 2. User API | |
30 | ||
31 | int rproc_boot(struct rproc *rproc) | |
32 | - Boot a remote processor (i.e. load its firmware, power it on, ...). | |
33 | If the remote processor is already powered on, this function immediately | |
34 | returns (successfully). | |
35 | Returns 0 on success, and an appropriate error value otherwise. | |
36 | Note: to use this function you should already have a valid rproc | |
37 | handle. There are several ways to achieve that cleanly (devres, pdata, | |
38 | the way remoteproc_rpmsg.c does this, or, if this becomes prevalent, we | |
39 | might also consider using dev_archdata for this). See also | |
40 | rproc_get_by_name() below. | |
41 | ||
42 | void rproc_shutdown(struct rproc *rproc) | |
43 | - Power off a remote processor (previously booted with rproc_boot()). | |
44 | In case @rproc is still being used by an additional user(s), then | |
45 | this function will just decrement the power refcount and exit, | |
46 | without really powering off the device. | |
47 | Every call to rproc_boot() must (eventually) be accompanied by a call | |
48 | to rproc_shutdown(). Calling rproc_shutdown() redundantly is a bug. | |
49 | Notes: | |
50 | - we're not decrementing the rproc's refcount, only the power refcount. | |
51 | which means that the @rproc handle stays valid even after | |
52 | rproc_shutdown() returns, and users can still use it with a subsequent | |
53 | rproc_boot(), if needed. | |
54 | - don't call rproc_shutdown() to unroll rproc_get_by_name(), exactly | |
55 | because rproc_shutdown() _does not_ decrement the refcount of @rproc. | |
56 | To decrement the refcount of @rproc, use rproc_put() (but _only_ if | |
57 | you acquired @rproc using rproc_get_by_name()). | |
58 | ||
59 | struct rproc *rproc_get_by_name(const char *name) | |
60 | - Find an rproc handle using the remote processor's name, and then | |
61 | boot it. If it's already powered on, then just immediately return | |
62 | (successfully). Returns the rproc handle on success, and NULL on failure. | |
63 | This function increments the remote processor's refcount, so always | |
64 | use rproc_put() to decrement it back once rproc isn't needed anymore. | |
65 | Note: currently rproc_get_by_name() and rproc_put() are not used anymore | |
66 | by the rpmsg bus and its drivers. We need to scrutinize the use cases | |
67 | that still need them, and see if we can migrate them to use the non | |
68 | name-based boot/shutdown interface. | |
69 | ||
70 | void rproc_put(struct rproc *rproc) | |
71 | - Decrement @rproc's power refcount and shut it down if it reaches zero | |
72 | (essentially by just calling rproc_shutdown), and then decrement @rproc's | |
73 | validity refcount too. | |
74 | After this function returns, @rproc may _not_ be used anymore, and its | |
75 | handle should be considered invalid. | |
76 | This function should be called _iff_ the @rproc handle was grabbed by | |
77 | calling rproc_get_by_name(). | |
78 | ||
79 | 3. Typical usage | |
80 | ||
81 | #include <linux/remoteproc.h> | |
82 | ||
83 | /* in case we were given a valid 'rproc' handle */ | |
84 | int dummy_rproc_example(struct rproc *my_rproc) | |
85 | { | |
86 | int ret; | |
87 | ||
88 | /* let's power on and boot our remote processor */ | |
89 | ret = rproc_boot(my_rproc); | |
90 | if (ret) { | |
91 | /* | |
92 | * something went wrong. handle it and leave. | |
93 | */ | |
94 | } | |
95 | ||
96 | /* | |
97 | * our remote processor is now powered on... give it some work | |
98 | */ | |
99 | ||
100 | /* let's shut it down now */ | |
101 | rproc_shutdown(my_rproc); | |
102 | } | |
103 | ||
104 | 4. API for implementors | |
105 | ||
106 | struct rproc *rproc_alloc(struct device *dev, const char *name, | |
107 | const struct rproc_ops *ops, | |
108 | const char *firmware, int len) | |
109 | - Allocate a new remote processor handle, but don't register | |
110 | it yet. Required parameters are the underlying device, the | |
111 | name of this remote processor, platform-specific ops handlers, | |
112 | the name of the firmware to boot this rproc with, and the | |
113 | length of private data needed by the allocating rproc driver (in bytes). | |
114 | ||
115 | This function should be used by rproc implementations during | |
116 | initialization of the remote processor. | |
117 | After creating an rproc handle using this function, and when ready, | |
118 | implementations should then call rproc_register() to complete | |
119 | the registration of the remote processor. | |
120 | On success, the new rproc is returned, and on failure, NULL. | |
121 | ||
122 | Note: _never_ directly deallocate @rproc, even if it was not registered | |
123 | yet. Instead, if you just need to unroll rproc_alloc(), use rproc_free(). | |
124 | ||
125 | void rproc_free(struct rproc *rproc) | |
126 | - Free an rproc handle that was allocated by rproc_alloc. | |
127 | This function should _only_ be used if @rproc was only allocated, | |
128 | but not registered yet. | |
129 | If @rproc was already successfully registered (by calling | |
130 | rproc_register()), then use rproc_unregister() instead. | |
131 | ||
132 | int rproc_register(struct rproc *rproc) | |
133 | - Register @rproc with the remoteproc framework, after it has been | |
134 | allocated with rproc_alloc(). | |
135 | This is called by the platform-specific rproc implementation, whenever | |
136 | a new remote processor device is probed. | |
137 | Returns 0 on success and an appropriate error code otherwise. | |
138 | Note: this function initiates an asynchronous firmware loading | |
139 | context, which will look for virtio devices supported by the rproc's | |
140 | firmware. | |
141 | If found, those virtio devices will be created and added, so as a result | |
142 | of registering this remote processor, additional virtio drivers might get | |
143 | probed. | |
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144 | |
145 | int rproc_unregister(struct rproc *rproc) | |
146 | - Unregister a remote processor, and decrement its refcount. | |
147 | If its refcount drops to zero, then @rproc will be freed. If not, | |
148 | it will be freed later once the last reference is dropped. | |
149 | ||
150 | This function should be called when the platform specific rproc | |
151 | implementation decides to remove the rproc device. it should | |
152 | _only_ be called if a previous invocation of rproc_register() | |
153 | has completed successfully. | |
154 | ||
155 | After rproc_unregister() returns, @rproc is _not_ valid anymore and | |
156 | it shouldn't be used. More specifically, don't call rproc_free() | |
157 | or try to directly free @rproc after rproc_unregister() returns; | |
158 | none of these are needed, and calling them is a bug. | |
159 | ||
160 | Returns 0 on success and -EINVAL if @rproc isn't valid. | |
161 | ||
162 | 5. Implementation callbacks | |
163 | ||
164 | These callbacks should be provided by platform-specific remoteproc | |
165 | drivers: | |
166 | ||
167 | /** | |
168 | * struct rproc_ops - platform-specific device handlers | |
169 | * @start: power on the device and boot it | |
170 | * @stop: power off the device | |
171 | * @kick: kick a virtqueue (virtqueue id given as a parameter) | |
172 | */ | |
173 | struct rproc_ops { | |
174 | int (*start)(struct rproc *rproc); | |
175 | int (*stop)(struct rproc *rproc); | |
176 | void (*kick)(struct rproc *rproc, int vqid); | |
177 | }; | |
178 | ||
179 | Every remoteproc implementation should at least provide the ->start and ->stop | |
7a186941 | 180 | handlers. If rpmsg/virtio functionality is also desired, then the ->kick handler |
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181 | should be provided as well. |
182 | ||
183 | The ->start() handler takes an rproc handle and should then power on the | |
184 | device and boot it (use rproc->priv to access platform-specific private data). | |
185 | The boot address, in case needed, can be found in rproc->bootaddr (remoteproc | |
186 | core puts there the ELF entry point). | |
187 | On success, 0 should be returned, and on failure, an appropriate error code. | |
188 | ||
189 | The ->stop() handler takes an rproc handle and powers the device down. | |
190 | On success, 0 is returned, and on failure, an appropriate error code. | |
191 | ||
192 | The ->kick() handler takes an rproc handle, and an index of a virtqueue | |
193 | where new message was placed in. Implementations should interrupt the remote | |
194 | processor and let it know it has pending messages. Notifying remote processors | |
195 | the exact virtqueue index to look in is optional: it is easy (and not | |
196 | too expensive) to go through the existing virtqueues and look for new buffers | |
197 | in the used rings. | |
198 | ||
199 | 6. Binary Firmware Structure | |
200 | ||
201 | At this point remoteproc only supports ELF32 firmware binaries. However, | |
202 | it is quite expected that other platforms/devices which we'd want to | |
203 | support with this framework will be based on different binary formats. | |
204 | ||
205 | When those use cases show up, we will have to decouple the binary format | |
206 | from the framework core, so we can support several binary formats without | |
207 | duplicating common code. | |
208 | ||
209 | When the firmware is parsed, its various segments are loaded to memory | |
210 | according to the specified device address (might be a physical address | |
211 | if the remote processor is accessing memory directly). | |
212 | ||
213 | In addition to the standard ELF segments, most remote processors would | |
214 | also include a special section which we call "the resource table". | |
215 | ||
216 | The resource table contains system resources that the remote processor | |
217 | requires before it should be powered on, such as allocation of physically | |
218 | contiguous memory, or iommu mapping of certain on-chip peripherals. | |
219 | Remotecore will only power up the device after all the resource table's | |
220 | requirement are met. | |
221 | ||
222 | In addition to system resources, the resource table may also contain | |
223 | resource entries that publish the existence of supported features | |
224 | or configurations by the remote processor, such as trace buffers and | |
225 | supported virtio devices (and their configurations). | |
226 | ||
fd2c15ec | 227 | The resource table begins with this header: |
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228 | |
229 | /** | |
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230 | * struct resource_table - firmware resource table header |
231 | * @ver: version number | |
232 | * @num: number of resource entries | |
233 | * @reserved: reserved (must be zero) | |
234 | * @offset: array of offsets pointing at the various resource entries | |
235 | * | |
236 | * The header of the resource table, as expressed by this structure, | |
237 | * contains a version number (should we need to change this format in the | |
238 | * future), the number of available resource entries, and their offsets | |
239 | * in the table. | |
240 | */ | |
241 | struct resource_table { | |
242 | u32 ver; | |
243 | u32 num; | |
244 | u32 reserved[2]; | |
245 | u32 offset[0]; | |
246 | } __packed; | |
247 | ||
248 | Immediately following this header are the resource entries themselves, | |
249 | each of which begins with the following resource entry header: | |
250 | ||
251 | /** | |
252 | * struct fw_rsc_hdr - firmware resource entry header | |
400e64df | 253 | * @type: resource type |
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254 | * @data: resource data |
255 | * | |
256 | * Every resource entry begins with a 'struct fw_rsc_hdr' header providing | |
257 | * its @type. The content of the entry itself will immediately follow | |
258 | * this header, and it should be parsed according to the resource type. | |
400e64df | 259 | */ |
fd2c15ec | 260 | struct fw_rsc_hdr { |
400e64df | 261 | u32 type; |
fd2c15ec | 262 | u8 data[0]; |
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263 | } __packed; |
264 | ||
265 | Some resources entries are mere announcements, where the host is informed | |
266 | of specific remoteproc configuration. Other entries require the host to | |
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267 | do something (e.g. allocate a system resource). Sometimes a negotiation |
268 | is expected, where the firmware requests a resource, and once allocated, | |
269 | the host should provide back its details (e.g. address of an allocated | |
270 | memory region). | |
400e64df | 271 | |
fd2c15ec | 272 | Here are the various resource types that are currently supported: |
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273 | |
274 | /** | |
275 | * enum fw_resource_type - types of resource entries | |
276 | * | |
277 | * @RSC_CARVEOUT: request for allocation of a physically contiguous | |
278 | * memory region. | |
279 | * @RSC_DEVMEM: request to iommu_map a memory-based peripheral. | |
280 | * @RSC_TRACE: announces the availability of a trace buffer into which | |
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281 | * the remote processor will be writing logs. |
282 | * @RSC_VDEV: declare support for a virtio device, and serve as its | |
283 | * virtio header. | |
284 | * @RSC_LAST: just keep this one at the end | |
285 | * | |
286 | * Please note that these values are used as indices to the rproc_handle_rsc | |
287 | * lookup table, so please keep them sane. Moreover, @RSC_LAST is used to | |
288 | * check the validity of an index before the lookup table is accessed, so | |
289 | * please update it as needed. | |
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290 | */ |
291 | enum fw_resource_type { | |
292 | RSC_CARVEOUT = 0, | |
293 | RSC_DEVMEM = 1, | |
294 | RSC_TRACE = 2, | |
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295 | RSC_VDEV = 3, |
296 | RSC_LAST = 4, | |
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297 | }; |
298 | ||
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299 | For more details regarding a specific resource type, please see its |
300 | dedicated structure in include/linux/remoteproc.h. | |
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301 | |
302 | We also expect that platform-specific resource entries will show up | |
fd2c15ec | 303 | at some point. When that happens, we could easily add a new RSC_PLATFORM |
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304 | type, and hand those resources to the platform-specific rproc driver to handle. |
305 | ||
306 | 7. Virtio and remoteproc | |
307 | ||
308 | The firmware should provide remoteproc information about virtio devices | |
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309 | that it supports, and their configurations: a RSC_VDEV resource entry |
310 | should specify the virtio device id (as in virtio_ids.h), virtio features, | |
311 | virtio config space, vrings information, etc. | |
312 | ||
313 | When a new remote processor is registered, the remoteproc framework | |
314 | will look for its resource table and will register the virtio devices | |
315 | it supports. A firmware may support any number of virtio devices, and | |
316 | of any type (a single remote processor can also easily support several | |
317 | rpmsg virtio devices this way, if desired). | |
318 | ||
319 | Of course, RSC_VDEV resource entries are only good enough for static | |
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320 | allocation of virtio devices. Dynamic allocations will also be made possible |
321 | using the rpmsg bus (similar to how we already do dynamic allocations of | |
322 | rpmsg channels; read more about it in rpmsg.txt). |