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+Remote Processor Framework
+
+1. Introduction
+
+Modern SoCs typically have heterogeneous remote processor devices in asymmetric
+multiprocessing (AMP) configurations, which may be running different instances
+of operating system, whether it's Linux or any other flavor of real-time OS.
+
+OMAP4, for example, has dual Cortex-A9, dual Cortex-M3 and a C64x+ DSP.
+In a typical configuration, the dual cortex-A9 is running Linux in a SMP
+configuration, and each of the other three cores (two M3 cores and a DSP)
+is running its own instance of RTOS in an AMP configuration.
+
+The remoteproc framework allows different platforms/architectures to
+control (power on, load firmware, power off) those remote processors while
+abstracting the hardware differences, so the entire driver doesn't need to be
+duplicated. In addition, this framework also adds rpmsg virtio devices
+for remote processors that supports this kind of communication. This way,
+platform-specific remoteproc drivers only need to provide a few low-level
+handlers, and then all rpmsg drivers will then just work
+(for more information about the virtio-based rpmsg bus and its drivers,
+please read Documentation/rpmsg.txt).
+Registration of other types of virtio devices is now also possible. Firmwares
+just need to publish what kind of virtio devices do they support, and then
+remoteproc will add those devices. This makes it possible to reuse the
+existing virtio drivers with remote processor backends at a minimal development
+cost.
+
+2. User API
+
+  int rproc_boot(struct rproc *rproc)
+    - Boot a remote processor (i.e. load its firmware, power it on, ...).
+      If the remote processor is already powered on, this function immediately
+      returns (successfully).
+      Returns 0 on success, and an appropriate error value otherwise.
+      Note: to use this function you should already have a valid rproc
+      handle. There are several ways to achieve that cleanly (devres, pdata,
+      the way remoteproc_rpmsg.c does this, or, if this becomes prevalent, we
+      might also consider using dev_archdata for this).
+
+  void rproc_shutdown(struct rproc *rproc)
+    - Power off a remote processor (previously booted with rproc_boot()).
+      In case @rproc is still being used by an additional user(s), then
+      this function will just decrement the power refcount and exit,
+      without really powering off the device.
+      Every call to rproc_boot() must (eventually) be accompanied by a call
+      to rproc_shutdown(). Calling rproc_shutdown() redundantly is a bug.
+      Notes:
+      - we're not decrementing the rproc's refcount, only the power refcount.
+        which means that the @rproc handle stays valid even after
+        rproc_shutdown() returns, and users can still use it with a subsequent
+        rproc_boot(), if needed.
+
+3. Typical usage
+
+#include <linux/remoteproc.h>
+
+/* in case we were given a valid 'rproc' handle */
+int dummy_rproc_example(struct rproc *my_rproc)
+{
+	int ret;
+
+	/* let's power on and boot our remote processor */
+	ret = rproc_boot(my_rproc);
+	if (ret) {
+		/*
+		 * something went wrong. handle it and leave.
+		 */
+	}
+
+	/*
+	 * our remote processor is now powered on... give it some work
+	 */
+
+	/* let's shut it down now */
+	rproc_shutdown(my_rproc);
+}
+
+4. API for implementors
+
+  struct rproc *rproc_alloc(struct device *dev, const char *name,
+				const struct rproc_ops *ops,
+				const char *firmware, int len)
+    - Allocate a new remote processor handle, but don't register
+      it yet. Required parameters are the underlying device, the
+      name of this remote processor, platform-specific ops handlers,
+      the name of the firmware to boot this rproc with, and the
+      length of private data needed by the allocating rproc driver (in bytes).
+
+      This function should be used by rproc implementations during
+      initialization of the remote processor.
+      After creating an rproc handle using this function, and when ready,
+      implementations should then call rproc_add() to complete
+      the registration of the remote processor.
+      On success, the new rproc is returned, and on failure, NULL.
+
+      Note: _never_ directly deallocate @rproc, even if it was not registered
+      yet. Instead, when you need to unroll rproc_alloc(), use rproc_put().
+
+  void rproc_put(struct rproc *rproc)
+    - Free an rproc handle that was allocated by rproc_alloc.
+      This function essentially unrolls rproc_alloc(), by decrementing the
+      rproc's refcount. It doesn't directly free rproc; that would happen
+      only if there are no other references to rproc and its refcount now
+      dropped to zero.
+
+  int rproc_add(struct rproc *rproc)
+    - Register @rproc with the remoteproc framework, after it has been
+      allocated with rproc_alloc().
+      This is called by the platform-specific rproc implementation, whenever
+      a new remote processor device is probed.
+      Returns 0 on success and an appropriate error code otherwise.
+      Note: this function initiates an asynchronous firmware loading
+      context, which will look for virtio devices supported by the rproc's
+      firmware.
+      If found, those virtio devices will be created and added, so as a result
+      of registering this remote processor, additional virtio drivers might get
+      probed.
+
+  int rproc_del(struct rproc *rproc)
+    - Unroll rproc_add().
+      This function should be called when the platform specific rproc
+      implementation decides to remove the rproc device. it should
+      _only_ be called if a previous invocation of rproc_add()
+      has completed successfully.
+
+      After rproc_del() returns, @rproc is still valid, and its
+      last refcount should be decremented by calling rproc_put().
+
+      Returns 0 on success and -EINVAL if @rproc isn't valid.
+
+  void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type)
+    - Report a crash in a remoteproc
+      This function must be called every time a crash is detected by the
+      platform specific rproc implementation. This should not be called from a
+      non-remoteproc driver. This function can be called from atomic/interrupt
+      context.
+
+5. Implementation callbacks
+
+These callbacks should be provided by platform-specific remoteproc
+drivers:
+
+/**
+ * struct rproc_ops - platform-specific device handlers
+ * @start:	power on the device and boot it
+ * @stop:	power off the device
+ * @kick:	kick a virtqueue (virtqueue id given as a parameter)
+ */
+struct rproc_ops {
+	int (*start)(struct rproc *rproc);
+	int (*stop)(struct rproc *rproc);
+	void (*kick)(struct rproc *rproc, int vqid);
+};
+
+Every remoteproc implementation should at least provide the ->start and ->stop
+handlers. If rpmsg/virtio functionality is also desired, then the ->kick handler
+should be provided as well.
+
+The ->start() handler takes an rproc handle and should then power on the
+device and boot it (use rproc->priv to access platform-specific private data).
+The boot address, in case needed, can be found in rproc->bootaddr (remoteproc
+core puts there the ELF entry point).
+On success, 0 should be returned, and on failure, an appropriate error code.
+
+The ->stop() handler takes an rproc handle and powers the device down.
+On success, 0 is returned, and on failure, an appropriate error code.
+
+The ->kick() handler takes an rproc handle, and an index of a virtqueue
+where new message was placed in. Implementations should interrupt the remote
+processor and let it know it has pending messages. Notifying remote processors
+the exact virtqueue index to look in is optional: it is easy (and not
+too expensive) to go through the existing virtqueues and look for new buffers
+in the used rings.
+
+6. Binary Firmware Structure
+
+At this point remoteproc only supports ELF32 firmware binaries. However,
+it is quite expected that other platforms/devices which we'd want to
+support with this framework will be based on different binary formats.
+
+When those use cases show up, we will have to decouple the binary format
+from the framework core, so we can support several binary formats without
+duplicating common code.
+
+When the firmware is parsed, its various segments are loaded to memory
+according to the specified device address (might be a physical address
+if the remote processor is accessing memory directly).
+
+In addition to the standard ELF segments, most remote processors would
+also include a special section which we call "the resource table".
+
+The resource table contains system resources that the remote processor
+requires before it should be powered on, such as allocation of physically
+contiguous memory, or iommu mapping of certain on-chip peripherals.
+Remotecore will only power up the device after all the resource table's
+requirement are met.
+
+In addition to system resources, the resource table may also contain
+resource entries that publish the existence of supported features
+or configurations by the remote processor, such as trace buffers and
+supported virtio devices (and their configurations).
+
+The resource table begins with this header:
+
+/**
+ * struct resource_table - firmware resource table header
+ * @ver: version number
+ * @num: number of resource entries
+ * @reserved: reserved (must be zero)
+ * @offset: array of offsets pointing at the various resource entries
+ *
+ * The header of the resource table, as expressed by this structure,
+ * contains a version number (should we need to change this format in the
+ * future), the number of available resource entries, and their offsets
+ * in the table.
+ */
+struct resource_table {
+	u32 ver;
+	u32 num;
+	u32 reserved[2];
+	u32 offset[0];
+} __packed;
+
+Immediately following this header are the resource entries themselves,
+each of which begins with the following resource entry header:
+
+/**
+ * struct fw_rsc_hdr - firmware resource entry header
+ * @type: resource type
+ * @data: resource data
+ *
+ * Every resource entry begins with a 'struct fw_rsc_hdr' header providing
+ * its @type. The content of the entry itself will immediately follow
+ * this header, and it should be parsed according to the resource type.
+ */
+struct fw_rsc_hdr {
+	u32 type;
+	u8 data[0];
+} __packed;
+
+Some resources entries are mere announcements, where the host is informed
+of specific remoteproc configuration. Other entries require the host to
+do something (e.g. allocate a system resource). Sometimes a negotiation
+is expected, where the firmware requests a resource, and once allocated,
+the host should provide back its details (e.g. address of an allocated
+memory region).
+
+Here are the various resource types that are currently supported:
+
+/**
+ * enum fw_resource_type - types of resource entries
+ *
+ * @RSC_CARVEOUT:   request for allocation of a physically contiguous
+ *		    memory region.
+ * @RSC_DEVMEM:     request to iommu_map a memory-based peripheral.
+ * @RSC_TRACE:	    announces the availability of a trace buffer into which
+ *		    the remote processor will be writing logs.
+ * @RSC_VDEV:       declare support for a virtio device, and serve as its
+ *		    virtio header.
+ * @RSC_LAST:       just keep this one at the end
+ *
+ * Please note that these values are used as indices to the rproc_handle_rsc
+ * lookup table, so please keep them sane. Moreover, @RSC_LAST is used to
+ * check the validity of an index before the lookup table is accessed, so
+ * please update it as needed.
+ */
+enum fw_resource_type {
+	RSC_CARVEOUT	= 0,
+	RSC_DEVMEM	= 1,
+	RSC_TRACE	= 2,
+	RSC_VDEV	= 3,
+	RSC_LAST	= 4,
+};
+
+For more details regarding a specific resource type, please see its
+dedicated structure in include/linux/remoteproc.h.
+
+We also expect that platform-specific resource entries will show up
+at some point. When that happens, we could easily add a new RSC_PLATFORM
+type, and hand those resources to the platform-specific rproc driver to handle.
+
+7. Virtio and remoteproc
+
+The firmware should provide remoteproc information about virtio devices
+that it supports, and their configurations: a RSC_VDEV resource entry
+should specify the virtio device id (as in virtio_ids.h), virtio features,
+virtio config space, vrings information, etc.
+
+When a new remote processor is registered, the remoteproc framework
+will look for its resource table and will register the virtio devices
+it supports. A firmware may support any number of virtio devices, and
+of any type (a single remote processor can also easily support several
+rpmsg virtio devices this way, if desired).
+
+Of course, RSC_VDEV resource entries are only good enough for static
+allocation of virtio devices. Dynamic allocations will also be made possible
+using the rpmsg bus (similar to how we already do dynamic allocations of
+rpmsg channels; read more about it in rpmsg.txt).