From 57f0f512b273f60d52568b8c6b77e17f5636edc0 Mon Sep 17 00:00:00 2001 From: André Fabian Silva Delgado Date: Wed, 5 Aug 2015 17:04:01 -0300 Subject: Initial import --- arch/arm/include/asm/spinlock.h | 287 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 287 insertions(+) create mode 100644 arch/arm/include/asm/spinlock.h (limited to 'arch/arm/include/asm/spinlock.h') diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h new file mode 100644 index 000000000..0fa418463 --- /dev/null +++ b/arch/arm/include/asm/spinlock.h @@ -0,0 +1,287 @@ +#ifndef __ASM_SPINLOCK_H +#define __ASM_SPINLOCK_H + +#if __LINUX_ARM_ARCH__ < 6 +#error SMP not supported on pre-ARMv6 CPUs +#endif + +#include + +/* + * 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 unpredictableness, an approprite 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. + */ + +#define arch_spin_unlock_wait(lock) \ + do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0) + +#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock) + +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 = ACCESS_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(); +} + +/* write_can_lock - would write_trylock() succeed? */ +#define arch_write_can_lock(x) (ACCESS_ONCE((x)->lock) == 0) + +/* + * 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__( +"1: ldrex %0, [%2]\n" +" adds %0, %0, #1\n" +" strexpl %1, %0, [%2]\n" + WFE("mi") +" rsbpls %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; + } +} + +/* read_can_lock - would read_trylock() succeed? */ +#define arch_read_can_lock(x) (ACCESS_ONCE((x)->lock) < 0x80000000) + +#define arch_read_lock_flags(lock, flags) arch_read_lock(lock) +#define arch_write_lock_flags(lock, flags) arch_write_lock(lock) + +#define arch_spin_relax(lock) cpu_relax() +#define arch_read_relax(lock) cpu_relax() +#define arch_write_relax(lock) cpu_relax() + +#endif /* __ASM_SPINLOCK_H */ -- cgit v1.2.3-54-g00ecf