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  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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