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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:56 EST.

1	==========================
2	Remote Processor Framework
3	==========================
4	
5	Introduction
6	============
7	
8	Modern SoCs typically have heterogeneous remote processor devices in asymmetric
9	multiprocessing (AMP) configurations, which may be running different instances
10	of operating system, whether it's Linux or any other flavor of real-time OS.
11	
12	OMAP4, for example, has dual Cortex-A9, dual Cortex-M3 and a C64x+ DSP.
13	In a typical configuration, the dual cortex-A9 is running Linux in a SMP
14	configuration, and each of the other three cores (two M3 cores and a DSP)
15	is running its own instance of RTOS in an AMP configuration.
16	
17	The remoteproc framework allows different platforms/architectures to
18	control (power on, load firmware, power off) those remote processors while
19	abstracting the hardware differences, so the entire driver doesn't need to be
20	duplicated. In addition, this framework also adds rpmsg virtio devices
21	for remote processors that supports this kind of communication. This way,
22	platform-specific remoteproc drivers only need to provide a few low-level
23	handlers, and then all rpmsg drivers will then just work
24	(for more information about the virtio-based rpmsg bus and its drivers,
25	please read Documentation/rpmsg.txt).
26	Registration of other types of virtio devices is now also possible. Firmwares
27	just need to publish what kind of virtio devices do they support, and then
28	remoteproc will add those devices. This makes it possible to reuse the
29	existing virtio drivers with remote processor backends at a minimal development
30	cost.
31	
32	User API
33	========
34	
35	::
36	
37	  int rproc_boot(struct rproc *rproc)
38	
39	Boot a remote processor (i.e. load its firmware, power it on, ...).
40	
41	If the remote processor is already powered on, this function immediately
42	returns (successfully).
43	
44	Returns 0 on success, and an appropriate error value otherwise.
45	Note: to use this function you should already have a valid rproc
46	handle. There are several ways to achieve that cleanly (devres, pdata,
47	the way remoteproc_rpmsg.c does this, or, if this becomes prevalent, we
48	might also consider using dev_archdata for this).
49	
50	::
51	
52	  void rproc_shutdown(struct rproc *rproc)
53	
54	Power off a remote processor (previously booted with rproc_boot()).
55	In case @rproc is still being used by an additional user(s), then
56	this function will just decrement the power refcount and exit,
57	without really powering off the device.
58	
59	Every call to rproc_boot() must (eventually) be accompanied by a call
60	to rproc_shutdown(). Calling rproc_shutdown() redundantly is a bug.
61	
62	.. note::
63	
64	  we're not decrementing the rproc's refcount, only the power refcount.
65	  which means that the @rproc handle stays valid even after
66	  rproc_shutdown() returns, and users can still use it with a subsequent
67	  rproc_boot(), if needed.
68	
69	::
70	
71	  struct rproc *rproc_get_by_phandle(phandle phandle)
72	
73	Find an rproc handle using a device tree phandle. Returns the rproc
74	handle on success, and NULL on failure. This function increments
75	the remote processor's refcount, so always use rproc_put() to
76	decrement it back once rproc isn't needed anymore.
77	
78	Typical usage
79	=============
80	
81	::
82	
83	  #include <linux/remoteproc.h>
84	
85	  /* in case we were given a valid 'rproc' handle */
86	  int dummy_rproc_example(struct rproc *my_rproc)
87	  {
88		int ret;
89	
90		/* let's power on and boot our remote processor */
91		ret = rproc_boot(my_rproc);
92		if (ret) {
93			/*
94			 * something went wrong. handle it and leave.
95			 */
96		}
97	
98		/*
99		 * our remote processor is now powered on... give it some work
100		 */
101	
102		/* let's shut it down now */
103		rproc_shutdown(my_rproc);
104	  }
105	
106	API for implementors
107	====================
108	
109	::
110	
111	  struct rproc *rproc_alloc(struct device *dev, const char *name,
112					const struct rproc_ops *ops,
113					const char *firmware, int len)
114	
115	Allocate a new remote processor handle, but don't register
116	it yet. Required parameters are the underlying device, the
117	name of this remote processor, platform-specific ops handlers,
118	the name of the firmware to boot this rproc with, and the
119	length of private data needed by the allocating rproc driver (in bytes).
120	
121	This function should be used by rproc implementations during
122	initialization of the remote processor.
123	
124	After creating an rproc handle using this function, and when ready,
125	implementations should then call rproc_add() to complete
126	the registration of the remote processor.
127	
128	On success, the new rproc is returned, and on failure, NULL.
129	
130	.. note::
131	
132	  **never** directly deallocate @rproc, even if it was not registered
133	  yet. Instead, when you need to unroll rproc_alloc(), use rproc_free().
134	
135	::
136	
137	  void rproc_free(struct rproc *rproc)
138	
139	Free an rproc handle that was allocated by rproc_alloc.
140	
141	This function essentially unrolls rproc_alloc(), by decrementing the
142	rproc's refcount. It doesn't directly free rproc; that would happen
143	only if there are no other references to rproc and its refcount now
144	dropped to zero.
145	
146	::
147	
148	  int rproc_add(struct rproc *rproc)
149	
150	Register @rproc with the remoteproc framework, after it has been
151	allocated with rproc_alloc().
152	
153	This is called by the platform-specific rproc implementation, whenever
154	a new remote processor device is probed.
155	
156	Returns 0 on success and an appropriate error code otherwise.
157	Note: this function initiates an asynchronous firmware loading
158	context, which will look for virtio devices supported by the rproc's
159	firmware.
160	
161	If found, those virtio devices will be created and added, so as a result
162	of registering this remote processor, additional virtio drivers might get
163	probed.
164	
165	::
166	
167	  int rproc_del(struct rproc *rproc)
168	
169	Unroll rproc_add().
170	
171	This function should be called when the platform specific rproc
172	implementation decides to remove the rproc device. it should
173	_only_ be called if a previous invocation of rproc_add()
174	has completed successfully.
175	
176	After rproc_del() returns, @rproc is still valid, and its
177	last refcount should be decremented by calling rproc_free().
178	
179	Returns 0 on success and -EINVAL if @rproc isn't valid.
180	
181	::
182	
183	  void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type)
184	
185	Report a crash in a remoteproc
186	
187	This function must be called every time a crash is detected by the
188	platform specific rproc implementation. This should not be called from a
189	non-remoteproc driver. This function can be called from atomic/interrupt
190	context.
191	
192	Implementation callbacks
193	========================
194	
195	These callbacks should be provided by platform-specific remoteproc
196	drivers::
197	
198	  /**
199	   * struct rproc_ops - platform-specific device handlers
200	   * @start:	power on the device and boot it
201	   * @stop:	power off the device
202	   * @kick:	kick a virtqueue (virtqueue id given as a parameter)
203	   */
204	  struct rproc_ops {
205		int (*start)(struct rproc *rproc);
206		int (*stop)(struct rproc *rproc);
207		void (*kick)(struct rproc *rproc, int vqid);
208	  };
209	
210	Every remoteproc implementation should at least provide the ->start and ->stop
211	handlers. If rpmsg/virtio functionality is also desired, then the ->kick handler
212	should be provided as well.
213	
214	The ->start() handler takes an rproc handle and should then power on the
215	device and boot it (use rproc->priv to access platform-specific private data).
216	The boot address, in case needed, can be found in rproc->bootaddr (remoteproc
217	core puts there the ELF entry point).
218	On success, 0 should be returned, and on failure, an appropriate error code.
219	
220	The ->stop() handler takes an rproc handle and powers the device down.
221	On success, 0 is returned, and on failure, an appropriate error code.
222	
223	The ->kick() handler takes an rproc handle, and an index of a virtqueue
224	where new message was placed in. Implementations should interrupt the remote
225	processor and let it know it has pending messages. Notifying remote processors
226	the exact virtqueue index to look in is optional: it is easy (and not
227	too expensive) to go through the existing virtqueues and look for new buffers
228	in the used rings.
229	
230	Binary Firmware Structure
231	=========================
232	
233	At this point remoteproc only supports ELF32 firmware binaries. However,
234	it is quite expected that other platforms/devices which we'd want to
235	support with this framework will be based on different binary formats.
236	
237	When those use cases show up, we will have to decouple the binary format
238	from the framework core, so we can support several binary formats without
239	duplicating common code.
240	
241	When the firmware is parsed, its various segments are loaded to memory
242	according to the specified device address (might be a physical address
243	if the remote processor is accessing memory directly).
244	
245	In addition to the standard ELF segments, most remote processors would
246	also include a special section which we call "the resource table".
247	
248	The resource table contains system resources that the remote processor
249	requires before it should be powered on, such as allocation of physically
250	contiguous memory, or iommu mapping of certain on-chip peripherals.
251	Remotecore will only power up the device after all the resource table's
252	requirement are met.
253	
254	In addition to system resources, the resource table may also contain
255	resource entries that publish the existence of supported features
256	or configurations by the remote processor, such as trace buffers and
257	supported virtio devices (and their configurations).
258	
259	The resource table begins with this header::
260	
261	  /**
262	   * struct resource_table - firmware resource table header
263	   * @ver: version number
264	   * @num: number of resource entries
265	   * @reserved: reserved (must be zero)
266	   * @offset: array of offsets pointing at the various resource entries
267	   *
268	   * The header of the resource table, as expressed by this structure,
269	   * contains a version number (should we need to change this format in the
270	   * future), the number of available resource entries, and their offsets
271	   * in the table.
272	   */
273	  struct resource_table {
274		u32 ver;
275		u32 num;
276		u32 reserved[2];
277		u32 offset[0];
278	  } __packed;
279	
280	Immediately following this header are the resource entries themselves,
281	each of which begins with the following resource entry header::
282	
283	  /**
284	   * struct fw_rsc_hdr - firmware resource entry header
285	   * @type: resource type
286	   * @data: resource data
287	   *
288	   * Every resource entry begins with a 'struct fw_rsc_hdr' header providing
289	   * its @type. The content of the entry itself will immediately follow
290	   * this header, and it should be parsed according to the resource type.
291	   */
292	  struct fw_rsc_hdr {
293		u32 type;
294		u8 data[0];
295	  } __packed;
296	
297	Some resources entries are mere announcements, where the host is informed
298	of specific remoteproc configuration. Other entries require the host to
299	do something (e.g. allocate a system resource). Sometimes a negotiation
300	is expected, where the firmware requests a resource, and once allocated,
301	the host should provide back its details (e.g. address of an allocated
302	memory region).
303	
304	Here are the various resource types that are currently supported::
305	
306	  /**
307	   * enum fw_resource_type - types of resource entries
308	   *
309	   * @RSC_CARVEOUT:   request for allocation of a physically contiguous
310	   *		    memory region.
311	   * @RSC_DEVMEM:     request to iommu_map a memory-based peripheral.
312	   * @RSC_TRACE:	    announces the availability of a trace buffer into which
313	   *		    the remote processor will be writing logs.
314	   * @RSC_VDEV:       declare support for a virtio device, and serve as its
315	   *		    virtio header.
316	   * @RSC_LAST:       just keep this one at the end
317	   *
318	   * Please note that these values are used as indices to the rproc_handle_rsc
319	   * lookup table, so please keep them sane. Moreover, @RSC_LAST is used to
320	   * check the validity of an index before the lookup table is accessed, so
321	   * please update it as needed.
322	   */
323	  enum fw_resource_type {
324		RSC_CARVEOUT	= 0,
325		RSC_DEVMEM	= 1,
326		RSC_TRACE	= 2,
327		RSC_VDEV	= 3,
328		RSC_LAST	= 4,
329	  };
330	
331	For more details regarding a specific resource type, please see its
332	dedicated structure in include/linux/remoteproc.h.
333	
334	We also expect that platform-specific resource entries will show up
335	at some point. When that happens, we could easily add a new RSC_PLATFORM
336	type, and hand those resources to the platform-specific rproc driver to handle.
337	
338	Virtio and remoteproc
339	=====================
340	
341	The firmware should provide remoteproc information about virtio devices
342	that it supports, and their configurations: a RSC_VDEV resource entry
343	should specify the virtio device id (as in virtio_ids.h), virtio features,
344	virtio config space, vrings information, etc.
345	
346	When a new remote processor is registered, the remoteproc framework
347	will look for its resource table and will register the virtio devices
348	it supports. A firmware may support any number of virtio devices, and
349	of any type (a single remote processor can also easily support several
350	rpmsg virtio devices this way, if desired).
351	
352	Of course, RSC_VDEV resource entries are only good enough for static
353	allocation of virtio devices. Dynamic allocations will also be made possible
354	using the rpmsg bus (similar to how we already do dynamic allocations of
355	rpmsg channels; read more about it in rpmsg.txt).
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