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========================== Remote Processor Framework ========================== 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. 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. .. note:: 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. :: struct rproc *rproc_get_by_phandle(phandle phandle) Find an rproc handle using a device tree phandle. Returns the rproc handle on success, and NULL on failure. This function increments the remote processor's refcount, so always use rproc_put() to decrement it back once rproc isn't needed anymore. Typical usage ============= :: #include

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