/*
* Copyright (c) 2012, ARM Limited. All rights reserved.
*
* Redistribution and use in source and binary forms, with
* or without modification, are permitted provided that the
* following conditions are met:
*
* Redistributions of source code must retain the above
* copyright notice, this list of conditions and the
* following disclaimer.
*
* Redistributions in binary form must reproduce the
* above copyright notice, this list of conditions and
* the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* Neither the name of ARM nor the names of its
* contributors may be used to endorse or promote products
* derived from this software without specific prior written
* permission.
*/
/**
* Lamport's Bakery algorithm for spinlock handling
*
* Note that the algorithm requires the stack and the bakery struct
* to be in Strongly-Ordered memory.
*/
#include "appf_types.h"
#include "appf_internals.h"
#include "appf_helpers.h"
/**
* Initialize a bakery - only required if the bakery_t is
* on the stack or heap, as static data is zeroed anyway.
*/
void initialize_spinlock(bakery_t * bakery)
{
appf_memset(bakery, 0, sizeof(bakery_t));
}
/**
* Claim a bakery lock. Function does not return until
* lock has been obtained.
*/
void get_spinlock(unsigned cpuid, bakery_t * bakery)
{
unsigned i, max = 0, my_full_number, his_full_number;
/* Get a ticket */
bakery->entering[cpuid] = TRUE;
for (i = 0; i < MAX_CPUS; ++i) {
if (bakery->number[i] > max) {
max = bakery->number[i];
}
}
++max;
bakery->number[cpuid] = max;
bakery->entering[cpuid] = FALSE;
/* Wait for our turn */
my_full_number = (max << 8) + cpuid;
for (i = 0; i < MAX_CPUS; ++i) {
while (bakery->entering[i]) ; /* Wait */
do {
his_full_number = bakery->number[i];
if (his_full_number) {
his_full_number = (his_full_number << 8) + i;
}
}
while (his_full_number && (his_full_number < my_full_number));
}
dmb();
}
/**
* Release a bakery lock.
*/
void release_spinlock(unsigned cpuid, bakery_t * bakery)
{
dmb();
bakery->number[cpuid] = 0;
}