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