1========================== 2Remote Processor Framework 3========================== 4 5Introduction 6============ 7 8Modern SoCs typically have heterogeneous remote processor devices in asymmetric 9multiprocessing (AMP) configurations, which may be running different instances 10of operating system, whether it's Linux or any other flavor of real-time OS. 11 12OMAP4, for example, has dual Cortex-A9, dual Cortex-M3 and a C64x+ DSP. 13In a typical configuration, the dual cortex-A9 is running Linux in a SMP 14configuration, and each of the other three cores (two M3 cores and a DSP) 15is running its own instance of RTOS in an AMP configuration. 16 17The remoteproc framework allows different platforms/architectures to 18control (power on, load firmware, power off) those remote processors while 19abstracting the hardware differences, so the entire driver doesn't need to be 20duplicated. In addition, this framework also adds rpmsg virtio devices 21for remote processors that supports this kind of communication. This way, 22platform-specific remoteproc drivers only need to provide a few low-level 23handlers, and then all rpmsg drivers will then just work 24(for more information about the virtio-based rpmsg bus and its drivers, 25please read Documentation/staging/rpmsg.rst). 26Registration of other types of virtio devices is now also possible. Firmwares 27just need to publish what kind of virtio devices do they support, and then 28remoteproc will add those devices. This makes it possible to reuse the 29existing virtio drivers with remote processor backends at a minimal development 30cost. 31 32User API 33======== 34 35:: 36 37 int rproc_boot(struct rproc *rproc) 38 39Boot a remote processor (i.e. load its firmware, power it on, ...). 40 41If the remote processor is already powered on, this function immediately 42returns (successfully). 43 44Returns 0 on success, and an appropriate error value otherwise. 45Note: to use this function you should already have a valid rproc 46handle. There are several ways to achieve that cleanly (devres, pdata, 47the way remoteproc_rpmsg.c does this, or, if this becomes prevalent, we 48might also consider using dev_archdata for this). 49 50:: 51 52 int rproc_shutdown(struct rproc *rproc) 53 54Power off a remote processor (previously booted with rproc_boot()). 55In case @rproc is still being used by an additional user(s), then 56this function will just decrement the power refcount and exit, 57without really powering off the device. 58 59Returns 0 on success, and an appropriate error value otherwise. 60Every call to rproc_boot() must (eventually) be accompanied by a call 61to rproc_shutdown(). Calling rproc_shutdown() redundantly is a bug. 62 63.. note:: 64 65 we're not decrementing the rproc's refcount, only the power refcount. 66 which means that the @rproc handle stays valid even after 67 rproc_shutdown() returns, and users can still use it with a subsequent 68 rproc_boot(), if needed. 69 70:: 71 72 struct rproc *rproc_get_by_phandle(phandle phandle) 73 74Find an rproc handle using a device tree phandle. Returns the rproc 75handle on success, and NULL on failure. This function increments 76the remote processor's refcount, so always use rproc_put() to 77decrement it back once rproc isn't needed anymore. 78 79Typical usage 80============= 81 82:: 83 84 #include <linux/remoteproc.h> 85 86 /* in case we were given a valid 'rproc' handle */ 87 int dummy_rproc_example(struct rproc *my_rproc) 88 { 89 int ret; 90 91 /* let's power on and boot our remote processor */ 92 ret = rproc_boot(my_rproc); 93 if (ret) { 94 /* 95 * something went wrong. handle it and leave. 96 */ 97 } 98 99 /* 100 * our remote processor is now powered on... give it some work 101 */ 102 103 /* let's shut it down now */ 104 rproc_shutdown(my_rproc); 105 } 106 107API for implementors 108==================== 109 110:: 111 112 struct rproc *rproc_alloc(struct device *dev, const char *name, 113 const struct rproc_ops *ops, 114 const char *firmware, int len) 115 116Allocate a new remote processor handle, but don't register 117it yet. Required parameters are the underlying device, the 118name of this remote processor, platform-specific ops handlers, 119the name of the firmware to boot this rproc with, and the 120length of private data needed by the allocating rproc driver (in bytes). 121 122This function should be used by rproc implementations during 123initialization of the remote processor. 124 125After creating an rproc handle using this function, and when ready, 126implementations should then call rproc_add() to complete 127the registration of the remote processor. 128 129On success, the new rproc is returned, and on failure, NULL. 130 131.. note:: 132 133 **never** directly deallocate @rproc, even if it was not registered 134 yet. Instead, when you need to unroll rproc_alloc(), use rproc_free(). 135 136:: 137 138 void rproc_free(struct rproc *rproc) 139 140Free an rproc handle that was allocated by rproc_alloc. 141 142This function essentially unrolls rproc_alloc(), by decrementing the 143rproc's refcount. It doesn't directly free rproc; that would happen 144only if there are no other references to rproc and its refcount now 145dropped to zero. 146 147:: 148 149 int rproc_add(struct rproc *rproc) 150 151Register @rproc with the remoteproc framework, after it has been 152allocated with rproc_alloc(). 153 154This is called by the platform-specific rproc implementation, whenever 155a new remote processor device is probed. 156 157Returns 0 on success and an appropriate error code otherwise. 158Note: this function initiates an asynchronous firmware loading 159context, which will look for virtio devices supported by the rproc's 160firmware. 161 162If found, those virtio devices will be created and added, so as a result 163of registering this remote processor, additional virtio drivers might get 164probed. 165 166:: 167 168 int rproc_del(struct rproc *rproc) 169 170Unroll rproc_add(). 171 172This function should be called when the platform specific rproc 173implementation decides to remove the rproc device. it should 174_only_ be called if a previous invocation of rproc_add() 175has completed successfully. 176 177After rproc_del() returns, @rproc is still valid, and its 178last refcount should be decremented by calling rproc_free(). 179 180Returns 0 on success and -EINVAL if @rproc isn't valid. 181 182:: 183 184 void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type) 185 186Report a crash in a remoteproc 187 188This function must be called every time a crash is detected by the 189platform specific rproc implementation. This should not be called from a 190non-remoteproc driver. This function can be called from atomic/interrupt 191context. 192 193Implementation callbacks 194======================== 195 196These callbacks should be provided by platform-specific remoteproc 197drivers:: 198 199 /** 200 * struct rproc_ops - platform-specific device handlers 201 * @start: power on the device and boot it 202 * @stop: power off the device 203 * @kick: kick a virtqueue (virtqueue id given as a parameter) 204 */ 205 struct rproc_ops { 206 int (*start)(struct rproc *rproc); 207 int (*stop)(struct rproc *rproc); 208 void (*kick)(struct rproc *rproc, int vqid); 209 }; 210 211Every remoteproc implementation should at least provide the ->start and ->stop 212handlers. If rpmsg/virtio functionality is also desired, then the ->kick handler 213should be provided as well. 214 215The ->start() handler takes an rproc handle and should then power on the 216device and boot it (use rproc->priv to access platform-specific private data). 217The boot address, in case needed, can be found in rproc->bootaddr (remoteproc 218core puts there the ELF entry point). 219On success, 0 should be returned, and on failure, an appropriate error code. 220 221The ->stop() handler takes an rproc handle and powers the device down. 222On success, 0 is returned, and on failure, an appropriate error code. 223 224The ->kick() handler takes an rproc handle, and an index of a virtqueue 225where new message was placed in. Implementations should interrupt the remote 226processor and let it know it has pending messages. Notifying remote processors 227the exact virtqueue index to look in is optional: it is easy (and not 228too expensive) to go through the existing virtqueues and look for new buffers 229in the used rings. 230 231Binary Firmware Structure 232========================= 233 234At this point remoteproc supports ELF32 and ELF64 firmware binaries. However, 235it is quite expected that other platforms/devices which we'd want to 236support with this framework will be based on different binary formats. 237 238When those use cases show up, we will have to decouple the binary format 239from the framework core, so we can support several binary formats without 240duplicating common code. 241 242When the firmware is parsed, its various segments are loaded to memory 243according to the specified device address (might be a physical address 244if the remote processor is accessing memory directly). 245 246In addition to the standard ELF segments, most remote processors would 247also include a special section which we call "the resource table". 248 249The resource table contains system resources that the remote processor 250requires before it should be powered on, such as allocation of physically 251contiguous memory, or iommu mapping of certain on-chip peripherals. 252Remotecore will only power up the device after all the resource table's 253requirement are met. 254 255In addition to system resources, the resource table may also contain 256resource entries that publish the existence of supported features 257or configurations by the remote processor, such as trace buffers and 258supported virtio devices (and their configurations). 259 260The resource table begins with this header:: 261 262 /** 263 * struct resource_table - firmware resource table header 264 * @ver: version number 265 * @num: number of resource entries 266 * @reserved: reserved (must be zero) 267 * @offset: array of offsets pointing at the various resource entries 268 * 269 * The header of the resource table, as expressed by this structure, 270 * contains a version number (should we need to change this format in the 271 * future), the number of available resource entries, and their offsets 272 * in the table. 273 */ 274 struct resource_table { 275 u32 ver; 276 u32 num; 277 u32 reserved[2]; 278 u32 offset[0]; 279 } __packed; 280 281Immediately following this header are the resource entries themselves, 282each of which begins with the following resource entry header:: 283 284 /** 285 * struct fw_rsc_hdr - firmware resource entry header 286 * @type: resource type 287 * @data: resource data 288 * 289 * Every resource entry begins with a 'struct fw_rsc_hdr' header providing 290 * its @type. The content of the entry itself will immediately follow 291 * this header, and it should be parsed according to the resource type. 292 */ 293 struct fw_rsc_hdr { 294 u32 type; 295 u8 data[0]; 296 } __packed; 297 298Some resources entries are mere announcements, where the host is informed 299of specific remoteproc configuration. Other entries require the host to 300do something (e.g. allocate a system resource). Sometimes a negotiation 301is expected, where the firmware requests a resource, and once allocated, 302the host should provide back its details (e.g. address of an allocated 303memory region). 304 305Here are the various resource types that are currently supported:: 306 307 /** 308 * enum fw_resource_type - types of resource entries 309 * 310 * @RSC_CARVEOUT: request for allocation of a physically contiguous 311 * memory region. 312 * @RSC_DEVMEM: request to iommu_map a memory-based peripheral. 313 * @RSC_TRACE: announces the availability of a trace buffer into which 314 * the remote processor will be writing logs. 315 * @RSC_VDEV: declare support for a virtio device, and serve as its 316 * virtio header. 317 * @RSC_LAST: just keep this one at the end 318 * @RSC_VENDOR_START: start of the vendor specific resource types range 319 * @RSC_VENDOR_END: end of the vendor specific resource types range 320 * 321 * Please note that these values are used as indices to the rproc_handle_rsc 322 * lookup table, so please keep them sane. Moreover, @RSC_LAST is used to 323 * check the validity of an index before the lookup table is accessed, so 324 * please update it as needed. 325 */ 326 enum fw_resource_type { 327 RSC_CARVEOUT = 0, 328 RSC_DEVMEM = 1, 329 RSC_TRACE = 2, 330 RSC_VDEV = 3, 331 RSC_LAST = 4, 332 RSC_VENDOR_START = 128, 333 RSC_VENDOR_END = 512, 334 }; 335 336For more details regarding a specific resource type, please see its 337dedicated structure in include/linux/remoteproc.h. 338 339We also expect that platform-specific resource entries will show up 340at some point. When that happens, we could easily add a new RSC_PLATFORM 341type, and hand those resources to the platform-specific rproc driver to handle. 342 343Virtio and remoteproc 344===================== 345 346The firmware should provide remoteproc information about virtio devices 347that it supports, and their configurations: a RSC_VDEV resource entry 348should specify the virtio device id (as in virtio_ids.h), virtio features, 349virtio config space, vrings information, etc. 350 351When a new remote processor is registered, the remoteproc framework 352will look for its resource table and will register the virtio devices 353it supports. A firmware may support any number of virtio devices, and 354of any type (a single remote processor can also easily support several 355rpmsg virtio devices this way, if desired). 356 357Of course, RSC_VDEV resource entries are only good enough for static 358allocation of virtio devices. Dynamic allocations will also be made possible 359using the rpmsg bus (similar to how we already do dynamic allocations of 360rpmsg channels; read more about it in rpmsg.txt). 361