linux-imx

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Remote Processor Framework

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Introduction

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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.

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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.

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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.

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User API

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  int rproc_boot(struct rproc *rproc)

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Boot a remote processor (i.e. load its firmware, power it on, ...).

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If the remote processor is already powered on, this function immediately

returns (successfully).

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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).

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  void rproc_shutdown(struct rproc *rproc)

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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.

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Every call to rproc_boot() must (eventually) be accompanied by a call

to rproc_shutdown(). Calling rproc_shutdown() redundantly is a bug.

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.. note::

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