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/*
* 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
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* 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.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#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 */
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