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400e64d @ohadbc remoteproc: add framework for controlling remote processors
ohadbc authored
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
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39 might also consider using dev_archdata for this).
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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 3. Typical usage
55
56 #include <linux/remoteproc.h>
57
58 /* in case we were given a valid 'rproc' handle */
59 int dummy_rproc_example(struct rproc *my_rproc)
60 {
61 int ret;
62
63 /* let's power on and boot our remote processor */
64 ret = rproc_boot(my_rproc);
65 if (ret) {
66 /*
67 * something went wrong. handle it and leave.
68 */
69 }
70
71 /*
72 * our remote processor is now powered on... give it some work
73 */
74
75 /* let's shut it down now */
76 rproc_shutdown(my_rproc);
77 }
78
79 4. API for implementors
80
81 struct rproc *rproc_alloc(struct device *dev, const char *name,
82 const struct rproc_ops *ops,
83 const char *firmware, int len)
84 - Allocate a new remote processor handle, but don't register
85 it yet. Required parameters are the underlying device, the
86 name of this remote processor, platform-specific ops handlers,
87 the name of the firmware to boot this rproc with, and the
88 length of private data needed by the allocating rproc driver (in bytes).
89
90 This function should be used by rproc implementations during
91 initialization of the remote processor.
92 After creating an rproc handle using this function, and when ready,
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93 implementations should then call rproc_add() to complete
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94 the registration of the remote processor.
95 On success, the new rproc is returned, and on failure, NULL.
96
97 Note: _never_ directly deallocate @rproc, even if it was not registered
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98 yet. Instead, when you need to unroll rproc_alloc(), use rproc_put().
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99
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100 void rproc_put(struct rproc *rproc)
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101 - Free an rproc handle that was allocated by rproc_alloc.
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102 This function essentially unrolls rproc_alloc(), by decrementing the
103 rproc's refcount. It doesn't directly free rproc; that would happen
104 only if there are no other references to rproc and its refcount now
105 dropped to zero.
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106
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107 int rproc_add(struct rproc *rproc)
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108 - Register @rproc with the remoteproc framework, after it has been
109 allocated with rproc_alloc().
110 This is called by the platform-specific rproc implementation, whenever
111 a new remote processor device is probed.
112 Returns 0 on success and an appropriate error code otherwise.
113 Note: this function initiates an asynchronous firmware loading
114 context, which will look for virtio devices supported by the rproc's
115 firmware.
116 If found, those virtio devices will be created and added, so as a result
117 of registering this remote processor, additional virtio drivers might get
118 probed.
119
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120 int rproc_del(struct rproc *rproc)
121 - Unroll rproc_add().
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122 This function should be called when the platform specific rproc
123 implementation decides to remove the rproc device. it should
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124 _only_ be called if a previous invocation of rproc_add()
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125 has completed successfully.
126
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127 After rproc_del() returns, @rproc is still valid, and its
128 last refcount should be decremented by calling rproc_put().
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129
130 Returns 0 on success and -EINVAL if @rproc isn't valid.
131
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132 void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type)
133 - Report a crash in a remoteproc
134 This function must be called every time a crash is detected by the
135 platform specific rproc implementation. This should not be called from a
136 non-remoteproc driver. This function can be called from atomic/interrupt
137 context.
138
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139 5. Implementation callbacks
140
141 These callbacks should be provided by platform-specific remoteproc
142 drivers:
143
144 /**
145 * struct rproc_ops - platform-specific device handlers
146 * @start: power on the device and boot it
147 * @stop: power off the device
148 * @kick: kick a virtqueue (virtqueue id given as a parameter)
149 */
150 struct rproc_ops {
151 int (*start)(struct rproc *rproc);
152 int (*stop)(struct rproc *rproc);
153 void (*kick)(struct rproc *rproc, int vqid);
154 };
155
156 Every remoteproc implementation should at least provide the ->start and ->stop
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157 handlers. If rpmsg/virtio functionality is also desired, then the ->kick handler
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158 should be provided as well.
159
160 The ->start() handler takes an rproc handle and should then power on the
161 device and boot it (use rproc->priv to access platform-specific private data).
162 The boot address, in case needed, can be found in rproc->bootaddr (remoteproc
163 core puts there the ELF entry point).
164 On success, 0 should be returned, and on failure, an appropriate error code.
165
166 The ->stop() handler takes an rproc handle and powers the device down.
167 On success, 0 is returned, and on failure, an appropriate error code.
168
169 The ->kick() handler takes an rproc handle, and an index of a virtqueue
170 where new message was placed in. Implementations should interrupt the remote
171 processor and let it know it has pending messages. Notifying remote processors
172 the exact virtqueue index to look in is optional: it is easy (and not
173 too expensive) to go through the existing virtqueues and look for new buffers
174 in the used rings.
175
176 6. Binary Firmware Structure
177
178 At this point remoteproc only supports ELF32 firmware binaries. However,
179 it is quite expected that other platforms/devices which we'd want to
180 support with this framework will be based on different binary formats.
181
182 When those use cases show up, we will have to decouple the binary format
183 from the framework core, so we can support several binary formats without
184 duplicating common code.
185
186 When the firmware is parsed, its various segments are loaded to memory
187 according to the specified device address (might be a physical address
188 if the remote processor is accessing memory directly).
189
190 In addition to the standard ELF segments, most remote processors would
191 also include a special section which we call "the resource table".
192
193 The resource table contains system resources that the remote processor
194 requires before it should be powered on, such as allocation of physically
195 contiguous memory, or iommu mapping of certain on-chip peripherals.
196 Remotecore will only power up the device after all the resource table's
197 requirement are met.
198
199 In addition to system resources, the resource table may also contain
200 resource entries that publish the existence of supported features
201 or configurations by the remote processor, such as trace buffers and
202 supported virtio devices (and their configurations).
203
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204 The resource table begins with this header:
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205
206 /**
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207 * struct resource_table - firmware resource table header
208 * @ver: version number
209 * @num: number of resource entries
210 * @reserved: reserved (must be zero)
211 * @offset: array of offsets pointing at the various resource entries
212 *
213 * The header of the resource table, as expressed by this structure,
214 * contains a version number (should we need to change this format in the
215 * future), the number of available resource entries, and their offsets
216 * in the table.
217 */
218 struct resource_table {
219 u32 ver;
220 u32 num;
221 u32 reserved[2];
222 u32 offset[0];
223 } __packed;
224
225 Immediately following this header are the resource entries themselves,
226 each of which begins with the following resource entry header:
227
228 /**
229 * struct fw_rsc_hdr - firmware resource entry header
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230 * @type: resource type
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231 * @data: resource data
232 *
233 * Every resource entry begins with a 'struct fw_rsc_hdr' header providing
234 * its @type. The content of the entry itself will immediately follow
235 * this header, and it should be parsed according to the resource type.
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236 */
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237 struct fw_rsc_hdr {
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238 u32 type;
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239 u8 data[0];
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240 } __packed;
241
242 Some resources entries are mere announcements, where the host is informed
243 of specific remoteproc configuration. Other entries require the host to
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244 do something (e.g. allocate a system resource). Sometimes a negotiation
245 is expected, where the firmware requests a resource, and once allocated,
246 the host should provide back its details (e.g. address of an allocated
247 memory region).
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248
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249 Here are the various resource types that are currently supported:
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250
251 /**
252 * enum fw_resource_type - types of resource entries
253 *
254 * @RSC_CARVEOUT: request for allocation of a physically contiguous
255 * memory region.
256 * @RSC_DEVMEM: request to iommu_map a memory-based peripheral.
257 * @RSC_TRACE: announces the availability of a trace buffer into which
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258 * the remote processor will be writing logs.
259 * @RSC_VDEV: declare support for a virtio device, and serve as its
260 * virtio header.
261 * @RSC_LAST: just keep this one at the end
262 *
263 * Please note that these values are used as indices to the rproc_handle_rsc
264 * lookup table, so please keep them sane. Moreover, @RSC_LAST is used to
265 * check the validity of an index before the lookup table is accessed, so
266 * please update it as needed.
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267 */
268 enum fw_resource_type {
269 RSC_CARVEOUT = 0,
270 RSC_DEVMEM = 1,
271 RSC_TRACE = 2,
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272 RSC_VDEV = 3,
273 RSC_LAST = 4,
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274 };
275
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276 For more details regarding a specific resource type, please see its
277 dedicated structure in include/linux/remoteproc.h.
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278
279 We also expect that platform-specific resource entries will show up
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280 at some point. When that happens, we could easily add a new RSC_PLATFORM
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281 type, and hand those resources to the platform-specific rproc driver to handle.
282
283 7. Virtio and remoteproc
284
285 The firmware should provide remoteproc information about virtio devices
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286 that it supports, and their configurations: a RSC_VDEV resource entry
287 should specify the virtio device id (as in virtio_ids.h), virtio features,
288 virtio config space, vrings information, etc.
289
290 When a new remote processor is registered, the remoteproc framework
291 will look for its resource table and will register the virtio devices
292 it supports. A firmware may support any number of virtio devices, and
293 of any type (a single remote processor can also easily support several
294 rpmsg virtio devices this way, if desired).
295
296 Of course, RSC_VDEV resource entries are only good enough for static
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297 allocation of virtio devices. Dynamic allocations will also be made possible
298 using the rpmsg bus (similar to how we already do dynamic allocations of
299 rpmsg channels; read more about it in rpmsg.txt).
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