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4d8e2f135d
Replace the test-and-set spinlock implementation with ticket locks in order to get fairness (in form of FIFO order). The implementation uses a 32-bit wide struct, which consists of two 16-bit counters (owner and next). This is inspired by similar spinlock implementations on other architectures. This allows that the code works for both, RV32 and RV64. Signed-off-by: Christoph Muellner <cmuellner@linux.com> Reviewed-by: Anup Patel <anup.patel@wdc.com> Reviewed-by: Xiang W <wxjstz@126.com>
78 lines
1.6 KiB
C
78 lines
1.6 KiB
C
/*
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* SPDX-License-Identifier: BSD-2-Clause
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*
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* Copyright (c) 2019 Western Digital Corporation or its affiliates.
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* Copyright (c) 2021 Christoph Müllner <cmuellner@linux.com>
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*/
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#include <sbi/riscv_barrier.h>
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#include <sbi/riscv_locks.h>
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static inline int spin_lock_unlocked(spinlock_t lock)
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{
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return lock.owner == lock.next;
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}
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bool spin_lock_check(spinlock_t *lock)
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{
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RISCV_FENCE(r, rw);
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return !spin_lock_unlocked(*lock);
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}
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int spin_trylock(spinlock_t *lock)
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{
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unsigned long inc = 1u << TICKET_SHIFT;
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unsigned long mask = 0xffffu << TICKET_SHIFT;
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u32 l0, tmp1, tmp2;
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__asm__ __volatile__(
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/* Get the current lock counters. */
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"1: lr.w.aq %0, %3\n"
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" slli %2, %0, %6\n"
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" and %2, %2, %5\n"
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" and %1, %0, %5\n"
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/* Is the lock free right now? */
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" bne %1, %2, 2f\n"
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" add %0, %0, %4\n"
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/* Acquire the lock. */
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" sc.w.rl %0, %0, %3\n"
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" bnez %0, 1b\n"
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"2:"
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: "=&r"(l0), "=&r"(tmp1), "=&r"(tmp2), "+A"(*lock)
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: "r"(inc), "r"(mask), "I"(TICKET_SHIFT)
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: "memory");
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return !l0;
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}
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void spin_lock(spinlock_t *lock)
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{
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unsigned long inc = 1u << TICKET_SHIFT;
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unsigned long mask = 0xffffu;
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u32 l0, tmp1, tmp2;
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__asm__ __volatile__(
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/* Atomically increment the next ticket. */
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" amoadd.w.aqrl %0, %4, %3\n"
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/* Did we get the lock? */
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" srli %1, %0, %6\n"
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" and %1, %1, %5\n"
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"1: and %2, %0, %5\n"
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" beq %1, %2, 2f\n"
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/* If not, then spin on the lock. */
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" lw %0, %3\n"
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RISCV_ACQUIRE_BARRIER
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" j 1b\n"
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"2:"
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: "=&r"(l0), "=&r"(tmp1), "=&r"(tmp2), "+A"(*lock)
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: "r"(inc), "r"(mask), "I"(TICKET_SHIFT)
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: "memory");
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}
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void spin_unlock(spinlock_t *lock)
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{
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__smp_store_release(&lock->owner, lock->owner + 1);
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}
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