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3cfa500808
I removed this last week because of an incorrect comment:
smp_mb__after_spinlock() is actually still used, and is necessary on
RISC-V. It's been resurrected, with a comment that describes what it
actually does this time. Thanks to Andrea for finding the bug!
Fixes: 3343eb6806 ("RISC-V: Remove smb_mb__{before,after}_spinlock()")
CC: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
65 lines
2.1 KiB
C
65 lines
2.1 KiB
C
/*
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* Based on arch/arm/include/asm/barrier.h
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*
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* Copyright (C) 2012 ARM Ltd.
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* Copyright (C) 2013 Regents of the University of California
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* Copyright (C) 2017 SiFive
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef _ASM_RISCV_BARRIER_H
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#define _ASM_RISCV_BARRIER_H
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#ifndef __ASSEMBLY__
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#define nop() __asm__ __volatile__ ("nop")
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#define RISCV_FENCE(p, s) \
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__asm__ __volatile__ ("fence " #p "," #s : : : "memory")
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/* These barriers need to enforce ordering on both devices or memory. */
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#define mb() RISCV_FENCE(iorw,iorw)
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#define rmb() RISCV_FENCE(ir,ir)
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#define wmb() RISCV_FENCE(ow,ow)
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/* These barriers do not need to enforce ordering on devices, just memory. */
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#define smp_mb() RISCV_FENCE(rw,rw)
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#define smp_rmb() RISCV_FENCE(r,r)
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#define smp_wmb() RISCV_FENCE(w,w)
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/*
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* This is a very specific barrier: it's currently only used in two places in
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* the kernel, both in the scheduler. See include/linux/spinlock.h for the two
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* orderings it guarantees, but the "critical section is RCsc" guarantee
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* mandates a barrier on RISC-V. The sequence looks like:
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*
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* lr.aq lock
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* sc lock <= LOCKED
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* smp_mb__after_spinlock()
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* // critical section
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* lr lock
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* sc.rl lock <= UNLOCKED
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*
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* The AQ/RL pair provides a RCpc critical section, but there's not really any
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* way we can take advantage of that here because the ordering is only enforced
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* on that one lock. Thus, we're just doing a full fence.
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*/
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#define smp_mb__after_spinlock() RISCV_FENCE(rw,rw)
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#include <asm-generic/barrier.h>
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_RISCV_BARRIER_H */
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