/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H
#if __LINUX_ARM_ARCH__ < 6
#error SMP not supported on pre-ARMv6 CPUs
#endif
#include <linux/prefetch.h>
#include <asm/barrier.h>
#include <asm/processor.h>
/*
* sev and wfe are ARMv6K extensions. Uniprocessor ARMv6 may not have the K
* extensions, so when running on UP, we have to patch these instructions away.
*/
#ifdef CONFIG_THUMB2_KERNEL
/*
* For Thumb-2, special care is needed to ensure that the conditional WFE
* instruction really does assemble to exactly 4 bytes (as required by
* the SMP_ON_UP fixup code). By itself "wfene" might cause the
* assembler to insert a extra (16-bit) IT instruction, depending on the
* presence or absence of neighbouring conditional instructions.
*
* To avoid this unpredictability, an appropriate IT is inserted explicitly:
* the assembler won't change IT instructions which are explicitly present
* in the input.
*/
#define WFE(cond) __ALT_SMP_ASM( \
"it " cond "\n\t" \
"wfe" cond ".n", \
\
"nop.w" \
)
#else
#define WFE(cond) __ALT_SMP_ASM("wfe" cond, "nop")
#endif
#define SEV __ALT_SMP_ASM(WASM(sev), WASM(nop))
static inline void dsb_sev(void)
{
dsb(ishst);
__asm__(SEV);
}
/*
* ARMv6 ticket-based spin-locking.
*
* A memory barrier is required after we get a lock, and before we
* release it, because V6 CPUs are assumed to have weakly ordered
* memory.
*/
static inline void arch_spin_lock(arch_spinlock_t *lock)
{
unsigned long tmp;
u32 newval;
arch_spinlock_t lockval;
prefetchw(&lock->slock);
__asm__ __volatile__(
"1: ldrex %0, [%3]\n"
" add %1, %0, %4\n"
" strex %2, %1, [%3]\n"
" teq %2, #0\n"
" bne 1b"
: "=&r" (lockval), "=&r" (newval), "=&r" (tmp)
: "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
: "cc");
while (lockval.tickets.next != lockval.tickets.owner) {
wfe();
lockval.tickets.owner = READ_ONCE(lock->tickets.owner);
}
smp_mb();
}
static inline int arch_spin_trylock(arch_spinlock_t *lock)
{
unsigned long contended, res;
u32 slock;
prefetchw(&lock->slock);
do {
__asm__ __volatile__(
" ldrex %0, [%3]\n"
" mov %2, #0\n"
" subs %1, %0, %0, ror #16\n"
" addeq %0, %0, %4\n"
" strexeq %2, %0, [%3]"
: "=&r" (slock), "=&r" (contended), "=&r" (res)
: "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
: "cc");
} while (res);
if (!contended) {
smp_mb();
return 1;
} else {
return 0;
}
}
static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
smp_mb();
lock->tickets.owner++;
dsb_sev();
}
static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
return lock.tickets.owner == lock.tickets.next;
}
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
return !arch_spin_value_unlocked(READ_ONCE(*lock));
}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
struct __raw_tickets tickets = READ_ONCE(lock->tickets);
return (tickets.next - tickets.owner) > 1;
}
#define arch_spin_is_contended arch_spin_is_contended
/*
* RWLOCKS
*
*
* Write locks are easy - we just set bit 31. When unlocking, we can
* just write zero since the lock is exclusively held.
*/
static inline void arch_write_lock(arch_rwlock_t *rw)
{
unsigned long tmp;
prefetchw(&rw->lock);
__asm__ __volatile__(
"1: ldrex %0, [%1]\n"
" teq %0, #0\n"
WFE("ne")
" strexeq %0, %2, [%1]\n"
" teq %0, #0\n"
" bne 1b"
: "=&r" (tmp)
: "r" (&rw->lock), "r" (0x80000000)
: "cc");
smp_mb();
}
static inline int arch_write_trylock(arch_rwlock_t *rw)
{
unsigned long contended, res;
prefetchw(&rw->lock);
do {
__asm__ __volatile__(
" ldrex %0, [%2]\n"
" mov %1, #0\n"
" teq %0, #0\n"
" strexeq %1, %3, [%2]"
: "=&r" (contended), "=&r" (res)
: "r" (&rw->lock), "r" (0x80000000)
: "cc");
} while (res);
if (!contended) {
smp_mb();
return 1;
} else {
return 0;
}
}
static inline void arch_write_unlock(arch_rwlock_t *rw)
{
smp_mb();
__asm__ __volatile__(
"str %1, [%0]\n"
:
: "r" (&rw->lock), "r" (0)
: "cc");
dsb_sev();
}
/*
* Read locks are a bit more hairy:
* - Exclusively load the lock value.
* - Increment it.
* - Store new lock value if positive, and we still own this location.
* If the value is negative, we've already failed.
* - If we failed to store the value, we want a negative result.
* - If we failed, try again.
* Unlocking is similarly hairy. We may have multiple read locks
* currently active. However, we know we won't have any write
* locks.
*/
static inline void arch_read_lock(arch_rwlock_t *rw)
{
unsigned long tmp, tmp2;
prefetchw(&rw->lock);
__asm__ __volatile__(
" .syntax unified\n"
"1: ldrex %0, [%2]\n"
" adds %0, %0, #1\n"
" strexpl %1, %0, [%2]\n"
WFE("mi")
" rsbspl %0, %1, #0\n"
" bmi 1b"
: "=&r" (tmp), "=&r" (tmp2)
: "r" (&rw->lock)
: "cc");
smp_mb();
}
static inline void arch_read_unlock(arch_rwlock_t *rw)
{
unsigned long tmp, tmp2;
smp_mb();
prefetchw(&rw->lock);
__asm__ __volatile__(
"1: ldrex %0, [%2]\n"
" sub %0, %0, #1\n"
" strex %1, %0, [%2]\n"
" teq %1, #0\n"
" bne 1b"
: "=&r" (tmp), "=&r" (tmp2)
: "r" (&rw->lock)
: "cc");
if (tmp == 0)
dsb_sev();
}
static inline int arch_read_trylock(arch_rwlock_t *rw)
{
unsigned long contended, res;
prefetchw(&rw->lock);
do {
__asm__ __volatile__(
" ldrex %0, [%2]\n"
" mov %1, #0\n"
" adds %0, %0, #1\n"
" strexpl %1, %0, [%2]"
: "=&r" (contended), "=&r" (res)
: "r" (&rw->lock)
: "cc");
} while (res);
/* If the lock is negative, then it is already held for write. */
if (contended < 0x80000000) {
smp_mb();
return 1;
} else {
return 0;
}
}
#endif /* __ASM_SPINLOCK_H */
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