/* SPDX-License-Identifier: GPL-2.0-only */ /* * Based on arch/arm/include/asm/barrier.h * * Copyright (C) 2012 ARM Ltd. * Copyright (C) 2013 Regents of the University of California * Copyright (C) 2017 SiFive */ #ifndef _ASM_RISCV_BARRIER_H #define _ASM_RISCV_BARRIER_H #ifndef __ASSEMBLY__ #define nop() __asm__ __volatile__ ("nop") #define RISCV_FENCE(p, s) \ __asm__ __volatile__ ("fence " #p "," #s : : : "memory") /* These barriers need to enforce ordering on both devices or memory. */ #define mb() RISCV_FENCE(iorw,iorw) #define rmb() RISCV_FENCE(ir,ir) #define wmb() RISCV_FENCE(ow,ow) /* These barriers do not need to enforce ordering on devices, just memory. */ #define __smp_mb() RISCV_FENCE(rw,rw) #define __smp_rmb() RISCV_FENCE(r,r) #define __smp_wmb() RISCV_FENCE(w,w) #define __smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ RISCV_FENCE(rw,w); \ WRITE_ONCE(*p, v); \ } while (0) #define __smp_load_acquire(p) \ ({ \ typeof(*p) ___p1 = READ_ONCE(*p); \ compiletime_assert_atomic_type(*p); \ RISCV_FENCE(r,rw); \ ___p1; \ }) /* * This is a very specific barrier: it's currently only used in two places in * the kernel, both in the scheduler. See include/linux/spinlock.h for the two * orderings it guarantees, but the "critical section is RCsc" guarantee * mandates a barrier on RISC-V. The sequence looks like: * * lr.aq lock * sc lock <= LOCKED * smp_mb__after_spinlock() * // critical section * lr lock * sc.rl lock <= UNLOCKED * * The AQ/RL pair provides a RCpc critical section, but there's not really any * way we can take advantage of that here because the ordering is only enforced * on that one lock. Thus, we're just doing a full fence. * * Since we allow writeX to be called from preemptive regions we need at least * an "o" in the predecessor set to ensure device writes are visible before the * task is marked as available for scheduling on a new hart. While I don't see * any concrete reason we need a full IO fence, it seems safer to just upgrade * this in order to avoid any IO crossing a scheduling boundary. In both * instances the scheduler pairs this with an mb(), so nothing is necessary on * the new hart. */ #define smp_mb__after_spinlock() RISCV_FENCE(iorw,iorw) #include <asm-generic/barrier.h> #endif /* __ASSEMBLY__ */ #endif /* _ASM_RISCV_BARRIER_H */