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#ifndef _S390_RWSEM_H
#define _S390_RWSEM_H
/*
* S390 version
* Copyright IBM Corp. 2002
* Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
*
* Based on asm-alpha/semaphore.h and asm-i386/rwsem.h
*/
/*
*
* The MSW of the count is the negated number of active writers and waiting
* lockers, and the LSW is the total number of active locks
*
* The lock count is initialized to 0 (no active and no waiting lockers).
*
* When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
* uncontended lock. This can be determined because XADD returns the old value.
* Readers increment by 1 and see a positive value when uncontended, negative
* if there are writers (and maybe) readers waiting (in which case it goes to
* sleep).
*
* The value of WAITING_BIAS supports up to 32766 waiting processes. This can
* be extended to 65534 by manually checking the whole MSW rather than relying
* on the S flag.
*
* The value of ACTIVE_BIAS supports up to 65535 active processes.
*
* This should be totally fair - if anything is waiting, a process that wants a
* lock will go to the back of the queue. When the currently active lock is
* released, if there's a writer at the front of the queue, then that and only
* that will be woken up; if there's a bunch of consequtive readers at the
* front, then they'll all be woken up, but no other readers will be.
*/
#ifndef _LINUX_RWSEM_H
#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
#endif
#define RWSEM_UNLOCKED_VALUE 0x0000000000000000L
#define RWSEM_ACTIVE_BIAS 0x0000000000000001L
#define RWSEM_ACTIVE_MASK 0x00000000ffffffffL
#define RWSEM_WAITING_BIAS (-0x0000000100000000L)
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
/*
* lock for reading
*/
static inline void __down_read(struct rw_semaphore *sem)
{
signed long old, new;
asm volatile(
" lg %0,%2\n"
"0: lgr %1,%0\n"
" aghi %1,%4\n"
" csg %0,%1,%2\n"
" jl 0b"
: "=&d" (old), "=&d" (new), "=Q" (sem->count)
: "Q" (sem->count), "i" (RWSEM_ACTIVE_READ_BIAS)
: "cc", "memory");
if (old < 0)
rwsem_down_read_failed(sem);
}
/*
* trylock for reading -- returns 1 if successful, 0 if contention
*/
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
signed long old, new;
asm volatile(
" lg %0,%2\n"
"0: ltgr %1,%0\n"
" jm 1f\n"
" aghi %1,%4\n"
" csg %0,%1,%2\n"
" jl 0b\n"
"1:"
: "=&d" (old), "=&d" (new), "=Q" (sem->count)
: "Q" (sem->count), "i" (RWSEM_ACTIVE_READ_BIAS)
: "cc", "memory");
return old >= 0 ? 1 : 0;
}
/*
* lock for writing
*/
static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
signed long old, new, tmp;
tmp = RWSEM_ACTIVE_WRITE_BIAS;
asm volatile(
" lg %0,%2\n"
"0: lgr %1,%0\n"
" ag %1,%4\n"
" csg %0,%1,%2\n"
" jl 0b"
: "=&d" (old), "=&d" (new), "=Q" (sem->count)
: "Q" (sem->count), "m" (tmp)
: "cc", "memory");
if (old != 0)
rwsem_down_write_failed(sem);
}
static inline void __down_write(struct rw_semaphore *sem)
{
__down_write_nested(sem, 0);
}
/*
* trylock for writing -- returns 1 if successful, 0 if contention
*/
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
signed long old;
asm volatile(
" lg %0,%1\n"
"0: ltgr %0,%0\n"
" jnz 1f\n"
" csg %0,%3,%1\n"
" jl 0b\n"
"1:"
: "=&d" (old), "=Q" (sem->count)
: "Q" (sem->count), "d" (RWSEM_ACTIVE_WRITE_BIAS)
: "cc", "memory");
return (old == RWSEM_UNLOCKED_VALUE) ? 1 : 0;
}
/*
* unlock after reading
*/
static inline void __up_read(struct rw_semaphore *sem)
{
signed long old, new;
asm volatile(
" lg %0,%2\n"
"0: lgr %1,%0\n"
" aghi %1,%4\n"
" csg %0,%1,%2\n"
" jl 0b"
: "=&d" (old), "=&d" (new), "=Q" (sem->count)
: "Q" (sem->count), "i" (-RWSEM_ACTIVE_READ_BIAS)
: "cc", "memory");
if (new < 0)
if ((new & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
}
/*
* unlock after writing
*/
static inline void __up_write(struct rw_semaphore *sem)
{
signed long old, new, tmp;
tmp = -RWSEM_ACTIVE_WRITE_BIAS;
asm volatile(
" lg %0,%2\n"
"0: lgr %1,%0\n"
" ag %1,%4\n"
" csg %0,%1,%2\n"
" jl 0b"
: "=&d" (old), "=&d" (new), "=Q" (sem->count)
: "Q" (sem->count), "m" (tmp)
: "cc", "memory");
if (new < 0)
if ((new & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
}
/*
* downgrade write lock to read lock
*/
static inline void __downgrade_write(struct rw_semaphore *sem)
{
signed long old, new, tmp;
tmp = -RWSEM_WAITING_BIAS;
asm volatile(
" lg %0,%2\n"
"0: lgr %1,%0\n"
" ag %1,%4\n"
" csg %0,%1,%2\n"
" jl 0b"
: "=&d" (old), "=&d" (new), "=Q" (sem->count)
: "Q" (sem->count), "m" (tmp)
: "cc", "memory");
if (new > 1)
rwsem_downgrade_wake(sem);
}
/*
* implement atomic add functionality
*/
static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
{
signed long old, new;
asm volatile(
" lg %0,%2\n"
"0: lgr %1,%0\n"
" agr %1,%4\n"
" csg %0,%1,%2\n"
" jl 0b"
: "=&d" (old), "=&d" (new), "=Q" (sem->count)
: "Q" (sem->count), "d" (delta)
: "cc", "memory");
}
/*
* implement exchange and add functionality
*/
static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
{
signed long old, new;
asm volatile(
" lg %0,%2\n"
"0: lgr %1,%0\n"
" agr %1,%4\n"
" csg %0,%1,%2\n"
" jl 0b"
: "=&d" (old), "=&d" (new), "=Q" (sem->count)
: "Q" (sem->count), "d" (delta)
: "cc", "memory");
return new;
}
#endif /* _S390_RWSEM_H */
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