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Based on kernel version 4.9. Page generated on 2016-12-21 14:36 EST.

1	Remote Processor Framework
3	1. Introduction
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.
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.
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.
29	2. User API
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).
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.
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.
60	3. Typical usage
62	#include <linux/remoteproc.h>
64	/* in case we were given a valid 'rproc' handle */
65	int dummy_rproc_example(struct rproc *my_rproc)
66	{
67		int ret;
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		}
77		/*
78		 * our remote processor is now powered on... give it some work
79		 */
81		/* let's shut it down now */
82		rproc_shutdown(my_rproc);
83	}
85	4. API for implementors
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).
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.
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().
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.
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.
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.
133	      After rproc_del() returns, @rproc is still valid, and its
134	      last refcount should be decremented by calling rproc_free().
136	      Returns 0 on success and -EINVAL if @rproc isn't valid.
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.
145	5. Implementation callbacks
147	These callbacks should be provided by platform-specific remoteproc
148	drivers:
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	};
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.
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.
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.
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.
182	6. Binary Firmware Structure
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.
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.
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).
196	In addition to the standard ELF segments, most remote processors would
197	also include a special section which we call "the resource table".
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.
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).
210	The resource table begins with this header:
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;
231	Immediately following this header are the resource entries themselves,
232	each of which begins with the following resource entry header:
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;
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).
255	Here are the various resource types that are currently supported:
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	};
282	For more details regarding a specific resource type, please see its
283	dedicated structure in include/linux/remoteproc.h.
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.
289	7. Virtio and remoteproc
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.
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).
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).
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