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Based on kernel version 3.16. Page generated on 2014-08-06 21:40 EST.

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	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,
93	      implementations should then call rproc_add() to complete
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
98	      yet. Instead, when you need to unroll rproc_alloc(), use rproc_put().
99	
100	  void rproc_put(struct rproc *rproc)
101	    - Free an rproc handle that was allocated by rproc_alloc.
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.
106	
107	  int rproc_add(struct rproc *rproc)
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	
120	  int rproc_del(struct rproc *rproc)
121	    - Unroll rproc_add().
122	      This function should be called when the platform specific rproc
123	      implementation decides to remove the rproc device. it should
124	      _only_ be called if a previous invocation of rproc_add()
125	      has completed successfully.
126	
127	      After rproc_del() returns, @rproc is still valid, and its
128	      last refcount should be decremented by calling rproc_put().
129	
130	      Returns 0 on success and -EINVAL if @rproc isn't valid.
131	
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	
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
157	handlers. If rpmsg/virtio functionality is also desired, then the ->kick handler
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	
204	The resource table begins with this header:
205	
206	/**
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
230	 * @type: resource type
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.
236	 */
237	struct fw_rsc_hdr {
238		u32 type;
239		u8 data[0];
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
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).
248	
249	Here are the various resource types that are currently supported:
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
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.
267	 */
268	enum fw_resource_type {
269		RSC_CARVEOUT	= 0,
270		RSC_DEVMEM	= 1,
271		RSC_TRACE	= 2,
272		RSC_VDEV	= 3,
273		RSC_LAST	= 4,
274	};
275	
276	For more details regarding a specific resource type, please see its
277	dedicated structure in include/linux/remoteproc.h.
278	
279	We also expect that platform-specific resource entries will show up
280	at some point. When that happens, we could easily add a new RSC_PLATFORM
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
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
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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