110 lines
2.9 KiB
C
110 lines
2.9 KiB
C
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/*
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* Copyright 2010 Tilera Corporation. All Rights Reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for
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* more details.
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*
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* 32-bit SMP spinlocks.
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*/
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#ifndef _ASM_TILE_SPINLOCK_32_H
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#define _ASM_TILE_SPINLOCK_32_H
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#include <linux/atomic.h>
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#include <asm/page.h>
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#include <linux/compiler.h>
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/*
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* We only use even ticket numbers so the '1' inserted by a tns is
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* an unambiguous "ticket is busy" flag.
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*/
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#define TICKET_QUANTUM 2
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/*
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* SMP ticket spinlocks, allowing only a single CPU anywhere
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*
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* (the type definitions are in asm/spinlock_types.h)
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*/
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static inline int arch_spin_is_locked(arch_spinlock_t *lock)
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{
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/*
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* Note that even if a new ticket is in the process of being
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* acquired, so lock->next_ticket is 1, it's still reasonable
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* to claim the lock is held, since it will be momentarily
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* if not already. There's no need to wait for a "valid"
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* lock->next_ticket to become available.
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* Use READ_ONCE() to ensure that calling this in a loop is OK.
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*/
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int curr = READ_ONCE(lock->current_ticket);
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int next = READ_ONCE(lock->next_ticket);
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return next != curr;
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}
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void arch_spin_lock(arch_spinlock_t *lock);
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int arch_spin_trylock(arch_spinlock_t *lock);
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static inline void arch_spin_unlock(arch_spinlock_t *lock)
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{
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/* For efficiency, overlap fetching the old ticket with the wmb(). */
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int old_ticket = lock->current_ticket;
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wmb(); /* guarantee anything modified under the lock is visible */
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lock->current_ticket = old_ticket + TICKET_QUANTUM;
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}
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/*
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* Read-write spinlocks, allowing multiple readers
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* but only one writer.
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*
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* We use a "tns/store-back" technique on a single word to manage
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* the lock state, looping around to retry if the tns returns 1.
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*/
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/* Internal layout of the word; do not use. */
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#define _WR_NEXT_SHIFT 8
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#define _WR_CURR_SHIFT 16
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#define _WR_WIDTH 8
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#define _RD_COUNT_SHIFT 24
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#define _RD_COUNT_WIDTH 8
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/**
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* arch_read_lock() - acquire a read lock.
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*/
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void arch_read_lock(arch_rwlock_t *rwlock);
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/**
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* arch_write_lock() - acquire a write lock.
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*/
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void arch_write_lock(arch_rwlock_t *rwlock);
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/**
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* arch_read_trylock() - try to acquire a read lock.
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*/
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int arch_read_trylock(arch_rwlock_t *rwlock);
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/**
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* arch_write_trylock() - try to acquire a write lock.
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*/
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int arch_write_trylock(arch_rwlock_t *rwlock);
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/**
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* arch_read_unlock() - release a read lock.
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*/
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void arch_read_unlock(arch_rwlock_t *rwlock);
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/**
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* arch_write_unlock() - release a write lock.
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*/
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void arch_write_unlock(arch_rwlock_t *rwlock);
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#endif /* _ASM_TILE_SPINLOCK_32_H */
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