linux/Documentation/remoteproc.txt
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   1Remote Processor Framework
   2
   31. Introduction
   4
   5Modern SoCs typically have heterogeneous remote processor devices in asymmetric
   6multiprocessing (AMP) configurations, which may be running different instances
   7of operating system, whether it's Linux or any other flavor of real-time OS.
   8
   9OMAP4, for example, has dual Cortex-A9, dual Cortex-M3 and a C64x+ DSP.
  10In a typical configuration, the dual cortex-A9 is running Linux in a SMP
  11configuration, and each of the other three cores (two M3 cores and a DSP)
  12is running its own instance of RTOS in an AMP configuration.
  13
  14The remoteproc framework allows different platforms/architectures to
  15control (power on, load firmware, power off) those remote processors while
  16abstracting the hardware differences, so the entire driver doesn't need to be
  17duplicated. In addition, this framework also adds rpmsg virtio devices
  18for remote processors that supports this kind of communication. This way,
  19platform-specific remoteproc drivers only need to provide a few low-level
  20handlers, and then all rpmsg drivers will then just work
  21(for more information about the virtio-based rpmsg bus and its drivers,
  22please read Documentation/rpmsg.txt).
  23Registration of other types of virtio devices is now also possible. Firmwares
  24just need to publish what kind of virtio devices do they support, and then
  25remoteproc will add those devices. This makes it possible to reuse the
  26existing virtio drivers with remote processor backends at a minimal development
  27cost.
  28
  292. 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
  543. Typical usage
  55
  56#include <linux/remoteproc.h>
  57
  58/* in case we were given a valid 'rproc' handle */
  59int 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
  794. 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
 1325. Implementation callbacks
 133
 134These callbacks should be provided by platform-specific remoteproc
 135drivers:
 136
 137/**
 138 * struct rproc_ops - platform-specific device handlers
 139 * @start:      power on the device and boot it
 140 * @stop:       power off the device
 141 * @kick:       kick a virtqueue (virtqueue id given as a parameter)
 142 */
 143struct rproc_ops {
 144        int (*start)(struct rproc *rproc);
 145        int (*stop)(struct rproc *rproc);
 146        void (*kick)(struct rproc *rproc, int vqid);
 147};
 148
 149Every remoteproc implementation should at least provide the ->start and ->stop
 150handlers. If rpmsg/virtio functionality is also desired, then the ->kick handler
 151should be provided as well.
 152
 153The ->start() handler takes an rproc handle and should then power on the
 154device and boot it (use rproc->priv to access platform-specific private data).
 155The boot address, in case needed, can be found in rproc->bootaddr (remoteproc
 156core puts there the ELF entry point).
 157On success, 0 should be returned, and on failure, an appropriate error code.
 158
 159The ->stop() handler takes an rproc handle and powers the device down.
 160On success, 0 is returned, and on failure, an appropriate error code.
 161
 162The ->kick() handler takes an rproc handle, and an index of a virtqueue
 163where new message was placed in. Implementations should interrupt the remote
 164processor and let it know it has pending messages. Notifying remote processors
 165the exact virtqueue index to look in is optional: it is easy (and not
 166too expensive) to go through the existing virtqueues and look for new buffers
 167in the used rings.
 168
 1696. Binary Firmware Structure
 170
 171At this point remoteproc only supports ELF32 firmware binaries. However,
 172it is quite expected that other platforms/devices which we'd want to
 173support with this framework will be based on different binary formats.
 174
 175When those use cases show up, we will have to decouple the binary format
 176from the framework core, so we can support several binary formats without
 177duplicating common code.
 178
 179When the firmware is parsed, its various segments are loaded to memory
 180according to the specified device address (might be a physical address
 181if the remote processor is accessing memory directly).
 182
 183In addition to the standard ELF segments, most remote processors would
 184also include a special section which we call "the resource table".
 185
 186The resource table contains system resources that the remote processor
 187requires before it should be powered on, such as allocation of physically
 188contiguous memory, or iommu mapping of certain on-chip peripherals.
 189Remotecore will only power up the device after all the resource table's
 190requirement are met.
 191
 192In addition to system resources, the resource table may also contain
 193resource entries that publish the existence of supported features
 194or configurations by the remote processor, such as trace buffers and
 195supported virtio devices (and their configurations).
 196
 197The resource table begins with this header:
 198
 199/**
 200 * struct resource_table - firmware resource table header
 201 * @ver: version number
 202 * @num: number of resource entries
 203 * @reserved: reserved (must be zero)
 204 * @offset: array of offsets pointing at the various resource entries
 205 *
 206 * The header of the resource table, as expressed by this structure,
 207 * contains a version number (should we need to change this format in the
 208 * future), the number of available resource entries, and their offsets
 209 * in the table.
 210 */
 211struct resource_table {
 212        u32 ver;
 213        u32 num;
 214        u32 reserved[2];
 215        u32 offset[0];
 216} __packed;
 217
 218Immediately following this header are the resource entries themselves,
 219each of which begins with the following resource entry header:
 220
 221/**
 222 * struct fw_rsc_hdr - firmware resource entry header
 223 * @type: resource type
 224 * @data: resource data
 225 *
 226 * Every resource entry begins with a 'struct fw_rsc_hdr' header providing
 227 * its @type. The content of the entry itself will immediately follow
 228 * this header, and it should be parsed according to the resource type.
 229 */
 230struct fw_rsc_hdr {
 231        u32 type;
 232        u8 data[0];
 233} __packed;
 234
 235Some resources entries are mere announcements, where the host is informed
 236of specific remoteproc configuration. Other entries require the host to
 237do something (e.g. allocate a system resource). Sometimes a negotiation
 238is expected, where the firmware requests a resource, and once allocated,
 239the host should provide back its details (e.g. address of an allocated
 240memory region).
 241
 242Here are the various resource types that are currently supported:
 243
 244/**
 245 * enum fw_resource_type - types of resource entries
 246 *
 247 * @RSC_CARVEOUT:   request for allocation of a physically contiguous
 248 *                  memory region.
 249 * @RSC_DEVMEM:     request to iommu_map a memory-based peripheral.
 250 * @RSC_TRACE:      announces the availability of a trace buffer into which
 251 *                  the remote processor will be writing logs.
 252 * @RSC_VDEV:       declare support for a virtio device, and serve as its
 253 *                  virtio header.
 254 * @RSC_LAST:       just keep this one at the end
 255 *
 256 * Please note that these values are used as indices to the rproc_handle_rsc
 257 * lookup table, so please keep them sane. Moreover, @RSC_LAST is used to
 258 * check the validity of an index before the lookup table is accessed, so
 259 * please update it as needed.
 260 */
 261enum fw_resource_type {
 262        RSC_CARVEOUT    = 0,
 263        RSC_DEVMEM      = 1,
 264        RSC_TRACE       = 2,
 265        RSC_VDEV        = 3,
 266        RSC_LAST        = 4,
 267};
 268
 269For more details regarding a specific resource type, please see its
 270dedicated structure in include/linux/remoteproc.h.
 271
 272We also expect that platform-specific resource entries will show up
 273at some point. When that happens, we could easily add a new RSC_PLATFORM
 274type, and hand those resources to the platform-specific rproc driver to handle.
 275
 2767. Virtio and remoteproc
 277
 278The firmware should provide remoteproc information about virtio devices
 279that it supports, and their configurations: a RSC_VDEV resource entry
 280should specify the virtio device id (as in virtio_ids.h), virtio features,
 281virtio config space, vrings information, etc.
 282
 283When a new remote processor is registered, the remoteproc framework
 284will look for its resource table and will register the virtio devices
 285it supports. A firmware may support any number of virtio devices, and
 286of any type (a single remote processor can also easily support several
 287rpmsg virtio devices this way, if desired).
 288
 289Of course, RSC_VDEV resource entries are only good enough for static
 290allocation of virtio devices. Dynamic allocations will also be made possible
 291using the rpmsg bus (similar to how we already do dynamic allocations of
 292rpmsg channels; read more about it in rpmsg.txt).
 293
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