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/* $NetBSD: lock.h,v 1.23 2022/04/09 23:43:20 riastradh Exp $ */
/*-
* Copyright (c) 2001, 2007 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Wayne Knowles and Andrew Doran.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*
* Machine-dependent spin lock operations for MIPS processors.
*
* Note: R2000/R3000 doesn't have any atomic update instructions; this
* will cause problems for user applications using this header.
*/
#ifndef _MIPS_LOCK_H_
#define _MIPS_LOCK_H_
#include <sys/param.h>
#include <sys/atomic.h>
static __inline int
__SIMPLELOCK_LOCKED_P(const __cpu_simple_lock_t *__ptr)
{
return *__ptr != __SIMPLELOCK_UNLOCKED;
}
static __inline int
__SIMPLELOCK_UNLOCKED_P(const __cpu_simple_lock_t *__ptr)
{
return *__ptr == __SIMPLELOCK_UNLOCKED;
}
static __inline void
__cpu_simple_lock_clear(__cpu_simple_lock_t *__ptr)
{
*__ptr = __SIMPLELOCK_UNLOCKED;
}
static __inline void
__cpu_simple_lock_set(__cpu_simple_lock_t *__ptr)
{
*__ptr = __SIMPLELOCK_LOCKED;
}
#ifndef _HARDKERNEL
static __inline int
__cpu_simple_lock_try(__cpu_simple_lock_t *lp)
{
unsigned long t0, v0;
__asm volatile(
"# -- BEGIN __cpu_simple_lock_try\n"
" .set push \n"
" .set mips2 \n"
"1: ll %0, %4 \n"
" bnez %0, 2f \n"
" nop \n"
" li %0, %3 \n"
" sc %0, %2 \n"
" beqz %0, 2f \n"
" nop \n"
" li %1, 1 \n"
" sync \n"
" j 3f \n"
" nop \n"
" nop \n"
"2: li %1, 0 \n"
"3: \n"
" .set pop \n"
"# -- END __cpu_simple_lock_try \n"
: "=r" (t0), "=r" (v0), "+m" (*lp)
: "i" (__SIMPLELOCK_LOCKED), "m" (*lp));
return (v0 != 0);
}
#else /* !_HARDKERNEL */
u_int _atomic_cas_uint(volatile u_int *, u_int, u_int);
u_long _atomic_cas_ulong(volatile u_long *, u_long, u_long);
void * _atomic_cas_ptr(volatile void *, void *, void *);
static __inline int
__cpu_simple_lock_try(__cpu_simple_lock_t *lp)
{
/*
* Successful _atomic_cas_uint functions as a load-acquire --
* on MP systems, it issues sync after the LL/SC CAS succeeds;
* on non-MP systems every load is a load-acquire so it's moot.
* This pairs with the membar_release and store sequence in
* __cpu_simple_unlock that functions as a store-release
* operation.
*
* NOTE: This applies only to _atomic_cas_uint (with the
* underscore), in sys/arch/mips/mips/lock_stubs_*.S. Not true
* for atomic_cas_uint (without the underscore), from
* common/lib/libc/arch/mips/atomic/atomic_cas.S which does not
* imply a load-acquire. It is unclear why these disagree.
*/
return _atomic_cas_uint(lp,
__SIMPLELOCK_UNLOCKED, __SIMPLELOCK_LOCKED) ==
__SIMPLELOCK_UNLOCKED;
}
#endif /* _HARDKERNEL */
static __inline void
__cpu_simple_lock_init(__cpu_simple_lock_t *lp)
{
*lp = __SIMPLELOCK_UNLOCKED;
}
static __inline void
__cpu_simple_lock(__cpu_simple_lock_t *lp)
{
while (!__cpu_simple_lock_try(lp)) {
while (*lp == __SIMPLELOCK_LOCKED)
/* spin */;
}
}
static __inline void
__cpu_simple_unlock(__cpu_simple_lock_t *lp)
{
/*
* The membar_release and then store functions as a
* store-release operation that pairs with the load-acquire
* operation in successful __cpu_simple_lock_try.
*
* Can't use atomic_store_release here because that's not
* available in userland at the moment.
*/
membar_release();
*lp = __SIMPLELOCK_UNLOCKED;
#ifdef _MIPS_ARCH_OCTEONP
/*
* On Cavium's recommendation, we issue an extra SYNCW that is
* not necessary for correct ordering because apparently stores
* can get stuck in Octeon store buffers for hundreds of
* thousands of cycles, according to the following note:
*
* Programming Notes:
* [...]
* Core A (writer)
* SW R1, DATA
* LI R2, 1
* SYNCW
* SW R2, FLAG
* SYNCW
* [...]
*
* The second SYNCW instruction executed by core A is not
* necessary for correctness, but has very important
* performance effects on OCTEON. Without it, the store
* to FLAG may linger in core A's write buffer before it
* becomes visible to other cores. (If core A is not
* performing many stores, this may add hundreds of
* thousands of cycles to the flag release time since the
* OCTEON core normally retains stores to attempt to merge
* them before sending the store on the CMB.)
* Applications should include this second SYNCW
* instruction after flag or lock releases.
*
* Cavium Networks OCTEON Plus CN50XX Hardware Reference
* Manual, July 2008, Appendix A, p. 943.
* https://storage.googleapis.com/google-code-archive-downloads/v2/code.google.com/hactive/CN50XX-HRM-V0.99E.pdf
*
* XXX It might be prudent to put this into
* atomic_store_release itself.
*/
__asm volatile("syncw" ::: "memory");
#endif
}
#endif /* _MIPS_LOCK_H_ */
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