linux-imx

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Hardware Spinlock Framework

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Introduction

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Hardware spinlock modules provide hardware assistance for synchronization

and mutual exclusion between heterogeneous processors and those not operating

under a single, shared operating system.

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For example, OMAP4 has dual Cortex-A9, dual Cortex-M3 and a C64x+ DSP,

each of which is running a different Operating System (the master, A9,

is usually running Linux and the slave processors, the M3 and the DSP,

are running some flavor of RTOS).

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A generic hwspinlock framework allows platform-independent drivers to use

the hwspinlock device in order to access data structures that are shared

between remote processors, that otherwise have no alternative mechanism

to accomplish synchronization and mutual exclusion operations.

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This is necessary, for example, for Inter-processor communications:

on OMAP4, cpu-intensive multimedia tasks are offloaded by the host to the

remote M3 and/or C64x+ slave processors (by an IPC subsystem called Syslink).

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To achieve fast message-based communications, a minimal kernel support

is needed to deliver messages arriving from a remote processor to the

appropriate user process.

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This communication is based on simple data structures that is shared between

the remote processors, and access to it is synchronized using the hwspinlock

module (remote processor directly places new messages in this shared data

structure).

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A common hwspinlock interface makes it possible to have generic, platform-

independent, drivers.

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User API

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  struct hwspinlock *hwspin_lock_request(void);

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Dynamically assign an hwspinlock and return its address, or NULL

in case an unused hwspinlock isn't available. Users of this

API will usually want to communicate the lock's id to the remote core

before it can be used to achieve synchronization.

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Should be called from a process context (might sleep).

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  struct hwspinlock *hwspin_lock_request_specific(unsigned int id);

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Assign a specific hwspinlock id and return its address, or NULL

if that hwspinlock is already in use. Usually board code will

be calling this function in order to reserve specific hwspinlock

ids for predefined purposes.

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Should be called from a process context (might sleep).

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