1Remote Processor Framework
   31. Introduction
   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.
   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.
  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
  292. 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). See also
  40      rproc_get_by_name() below.
  42  void rproc_shutdown(struct rproc *rproc)
  43    - Power off a remote processor (previously booted with rproc_boot()).
  44      In case @rproc is still being used by an additional user(s), then
  45      this function will just decrement the power refcount and exit,
  46      without really powering off the device.
  47      Every call to rproc_boot() must (eventually) be accompanied by a call
  48      to rproc_shutdown(). Calling rproc_shutdown() redundantly is a bug.
  49      Notes:
  50      - we're not decrementing the rproc's refcount, only the power refcount.
  51        which means that the @rproc handle stays valid even after
  52        rproc_shutdown() returns, and users can still use it with a subsequent
  53        rproc_boot(), if needed.
  54      - don't call rproc_shutdown() to unroll rproc_get_by_name(), exactly
  55        because rproc_shutdown() _does not_ decrement the refcount of @rproc.
  56        To decrement the refcount of @rproc, use rproc_put() (but _only_ if
  57        you acquired @rproc using rproc_get_by_name()).
  59  struct rproc *rproc_get_by_name(const char *name)
  60    - Find an rproc handle using the remote processor's name, and then
  61      boot it. If it's already powered on, then just immediately return
  62      (successfully). Returns the rproc handle on success, and NULL on failure.
  63      This function increments the remote processor's refcount, so always
  64      use rproc_put() to decrement it back once rproc isn't needed anymore.
  65      Note: currently rproc_get_by_name() and rproc_put() are not used anymore
  66      by the rpmsg bus and its drivers. We need to scrutinize the use cases
  67      that still need them, and see if we can migrate them to use the non
  68      name-based boot/shutdown interface.
  70  void rproc_put(struct rproc *rproc)
  71    - Decrement @rproc's power refcount and shut it down if it reaches zero
  72      (essentially by just calling rproc_shutdown), and then decrement @rproc's
  73      validity refcount too.
  74      After this function returns, @rproc may _not_ be used anymore, and its
  75      handle should be considered invalid.
  76      This function should be called _iff_ the @rproc handle was grabbed by
  77      calling rproc_get_by_name().
  793. Typical usage
  81#include <linux/remoteproc.h>
  83/* in case we were given a valid 'rproc' handle */
  84int dummy_rproc_example(struct rproc *my_rproc)
  86        int ret;
  88        /* let's power on and boot our remote processor */
  89        ret = rproc_boot(my_rproc);
  90        if (ret) {
  91                /*
  92                 * something went wrong. handle it and leave.
  93                 */
  94        }
  96        /*
  97         * our remote processor is now powered on... give it some work
  98         */
 100        /* let's shut it down now */
 101        rproc_shutdown(my_rproc);
 1044. API for implementors
 106  struct rproc *rproc_alloc(struct device *dev, const char *name,
 107                                const struct rproc_ops *ops,
 108                                const char *firmware, int len)
 109    - Allocate a new remote processor handle, but don't register
 110      it yet. Required parameters are the underlying device, the
 111      name of this remote processor, platform-specific ops handlers,
 112      the name of the firmware to boot this rproc with, and the
 113      length of private data needed by the allocating rproc driver (in bytes).
 115      This function should be used by rproc implementations during
 116      initialization of the remote processor.
 117      After creating an rproc handle using this function, and when ready,
 118      implementations should then call rproc_register() to complete
 119      the registration of the remote processor.
 120      On success, the new rproc is returned, and on failure, NULL.
 122      Note: _never_ directly deallocate @rproc, even if it was not registered
 123      yet. Instead, if you just need to unroll rproc_alloc(), use rproc_free().
 125  void rproc_free(struct rproc *rproc)
 126    - Free an rproc handle that was allocated by rproc_alloc.
 127      This function should _only_ be used if @rproc was only allocated,
 128      but not registered yet.
 129      If @rproc was already successfully registered (by calling
 130      rproc_register()), then use rproc_unregister() instead.
 132  int rproc_register(struct rproc *rproc)
 133    - Register @rproc with the remoteproc framework, after it has been
 134      allocated with rproc_alloc().
 135      This is called by the platform-specific rproc implementation, whenever
 136      a new remote processor device is probed.
 137      Returns 0 on success and an appropriate error code otherwise.
 138      Note: this function initiates an asynchronous firmware loading
 139      context, which will look for virtio devices supported by the rproc's
 140      firmware.
 141      If found, those virtio devices will be created and added, so as a result
 142      of registering this remote processor, additional virtio drivers might get
 143      probed.
 145  int rproc_unregister(struct rproc *rproc)
 146    - Unregister a remote processor, and decrement its refcount.
 147      If its refcount drops to zero, then @rproc will be freed. If not,
 148      it will be freed later once the last reference is dropped.
 150      This function should be called when the platform specific rproc
 151      implementation decides to remove the rproc device. it should
 152      _only_ be called if a previous invocation of rproc_register()
 153      has completed successfully.
 155      After rproc_unregister() returns, @rproc is _not_ valid anymore and
 156      it shouldn't be used. More specifically, don't call rproc_free()
 157      or try to directly free @rproc after rproc_unregister() returns;
 158      none of these are needed, and calling them is a bug.
 160      Returns 0 on success and -EINVAL if @rproc isn't valid.
 1625. Implementation callbacks
 164These callbacks should be provided by platform-specific remoteproc
 168 * struct rproc_ops - platform-specific device handlers
 169 * @start:      power on the device and boot it
 170 * @stop:       power off the device
 171 * @kick:       kick a virtqueue (virtqueue id given as a parameter)
 172 */
 173struct rproc_ops {
 174        int (*start)(struct rproc *rproc);
 175        int (*stop)(struct rproc *rproc);
 176        void (*kick)(struct rproc *rproc, int vqid);
 179Every remoteproc implementation should at least provide the ->start and ->stop
 180handlers. If rpmsg/virtio functionality is also desired, then the ->kick handler
 181should be provided as well.
 183The ->start() handler takes an rproc handle and should then power on the
 184device and boot it (use rproc->priv to access platform-specific private data).
 185The boot address, in case needed, can be found in rproc->bootaddr (remoteproc
 186core puts there the ELF entry point).
 187On success, 0 should be returned, and on failure, an appropriate error code.
 189The ->stop() handler takes an rproc handle and powers the device down.
 190On success, 0 is returned, and on failure, an appropriate error code.
 192The ->kick() handler takes an rproc handle, and an index of a virtqueue
 193where new message was placed in. Implementations should interrupt the remote
 194processor and let it know it has pending messages. Notifying remote processors
 195the exact virtqueue index to look in is optional: it is easy (and not
 196too expensive) to go through the existing virtqueues and look for new buffers
 197in the used rings.
 1996. Binary Firmware Structure
 201At this point remoteproc only supports ELF32 firmware binaries. However,
 202it is quite expected that other platforms/devices which we'd want to
 203support with this framework will be based on different binary formats.
 205When those use cases show up, we will have to decouple the binary format
 206from the framework core, so we can support several binary formats without
 207duplicating common code.
 209When the firmware is parsed, its various segments are loaded to memory
 210according to the specified device address (might be a physical address
 211if the remote processor is accessing memory directly).
 213In addition to the standard ELF segments, most remote processors would
 214also include a special section which we call "the resource table".
 216The resource table contains system resources that the remote processor
 217requires before it should be powered on, such as allocation of physically
 218contiguous memory, or iommu mapping of certain on-chip peripherals.
 219Remotecore will only power up the device after all the resource table's
 220requirement are met.
 222In addition to system resources, the resource table may also contain
 223resource entries that publish the existence of supported features
 224or configurations by the remote processor, such as trace buffers and
 225supported virtio devices (and their configurations).
 227The resource table begins with this header:
 230 * struct resource_table - firmware resource table header
 231 * @ver: version number
 232 * @num: number of resource entries
 233 * @reserved: reserved (must be zero)
 234 * @offset: array of offsets pointing at the various resource entries
 235 *
 236 * The header of the resource table, as expressed by this structure,
 237 * contains a version number (should we need to change this format in the
 238 * future), the number of available resource entries, and their offsets
 239 * in the table.
 240 */
 241struct resource_table {
 242        u32 ver;
 243        u32 num;
 244        u32 reserved[2];
 245        u32 offset[0];
 246} __packed;
 248Immediately following this header are the resource entries themselves,
 249each of which begins with the following resource entry header:
 252 * struct fw_rsc_hdr - firmware resource entry header
 253 * @type: resource type
 254 * @data: resource data
 255 *
 256 * Every resource entry begins with a 'struct fw_rsc_hdr' header providing
 257 * its @type. The content of the entry itself will immediately follow
 258 * this header, and it should be parsed according to the resource type.
 259 */
 260struct fw_rsc_hdr {
 261        u32 type;
 262        u8 data[0];
 263} __packed;
 265Some resources entries are mere announcements, where the host is informed
 266of specific remoteproc configuration. Other entries require the host to
 267do something (e.g. allocate a system resource). Sometimes a negotiation
 268is expected, where the firmware requests a resource, and once allocated,
 269the host should provide back its details (e.g. address of an allocated
 270memory region).
 272Here are the various resource types that are currently supported:
 275 * enum fw_resource_type - types of resource entries
 276 *
 277 * @RSC_CARVEOUT:   request for allocation of a physically contiguous
 278 *                  memory region.
 279 * @RSC_DEVMEM:     request to iommu_map a memory-based peripheral.
 280 * @RSC_TRACE:      announces the availability of a trace buffer into which
 281 *                  the remote processor will be writing logs.
 282 * @RSC_VDEV:       declare support for a virtio device, and serve as its
 283 *                  virtio header.
 284 * @RSC_LAST:       just keep this one at the end
 285 *
 286 * Please note that these values are used as indices to the rproc_handle_rsc
 287 * lookup table, so please keep them sane. Moreover, @RSC_LAST is used to
 288 * check the validity of an index before the lookup table is accessed, so
 289 * please update it as needed.
 290 */
 291enum fw_resource_type {
 292        RSC_CARVEOUT    = 0,
 293        RSC_DEVMEM      = 1,
 294        RSC_TRACE       = 2,
 295        RSC_VDEV        = 3,
 296        RSC_LAST        = 4,
 299For more details regarding a specific resource type, please see its
 300dedicated structure in include/linux/remoteproc.h.
 302We also expect that platform-specific resource entries will show up
 303at some point. When that happens, we could easily add a new RSC_PLATFORM
 304type, and hand those resources to the platform-specific rproc driver to handle.
 3067. Virtio and remoteproc
 308The firmware should provide remoteproc information about virtio devices
 309that it supports, and their configurations: a RSC_VDEV resource entry
 310should specify the virtio device id (as in virtio_ids.h), virtio features,
 311virtio config space, vrings information, etc.
 313When a new remote processor is registered, the remoteproc framework
 314will look for its resource table and will register the virtio devices
 315it supports. A firmware may support any number of virtio devices, and
 316of any type (a single remote processor can also easily support several
 317rpmsg virtio devices this way, if desired).
 319Of course, RSC_VDEV resource entries are only good enough for static
 320allocation of virtio devices. Dynamic allocations will also be made possible
 321using the rpmsg bus (similar to how we already do dynamic allocations of
 322rpmsg channels; read more about it in rpmsg.txt).
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