On Tue, Jun 06, 2017 at 04:00:03PM -0700, Palmer Dabbelt wrote:
> diff --git a/arch/riscv/include/asm/spinlock.h
> b/arch/riscv/include/asm/spinlock.h
> new file mode 100644
> index 000000000000..9736f5714e54
> --- /dev/null
> +++ b/arch/riscv/include/asm/spinlock.h
> @@ -0,0 +1,155 @@
> +/*
> + * Copyright (C) 2015 Regents of the University of California
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation, version 2.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#ifndef _ASM_RISCV_SPINLOCK_H
> +#define _ASM_RISCV_SPINLOCK_H
> +
> +#include <linux/kernel.h>
> +#include <asm/current.h>
> +
> +/*
> + * Simple spin lock operations. These provide no fairness guarantees.
> + */
Any reason to use a test-and-set spinlock at all?
> +
> +#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
> +#define arch_spin_is_locked(x) ((x)->lock != 0)
> +#define arch_spin_unlock_wait(x) \
> + do { cpu_relax(); } while ((x)->lock)
Hehe, yeah, no ;-) There are ordering constraints on that.
> +
> +static inline void arch_spin_unlock(arch_spinlock_t *lock)
> +{
> + __asm__ __volatile__ (
> + "amoswap.w.rl x0, x0, %0"
> + : "=A" (lock->lock)
> + :: "memory");
> +}
> +
> +static inline int arch_spin_trylock(arch_spinlock_t *lock)
> +{
> + int tmp = 1, busy;
> +
> + __asm__ __volatile__ (
> + "amoswap.w.aq %0, %2, %1"
> + : "=r" (busy), "+A" (lock->lock)
> + : "r" (tmp)
> + : "memory");
> +
> + return !busy;
> +}
> +
> +static inline void arch_spin_lock(arch_spinlock_t *lock)
> +{
> + while (1) {
> + if (arch_spin_is_locked(lock))
> + continue;
> +
> + if (arch_spin_trylock(lock))
> + break;
> + }
> +}
