1. 根目录:
2. include
3. asm-generic
4. system.h

/* Generic system definitions, based on MN10300 definitions.
 *
 * It should be possible to use these on really simple architectures,
 * but it serves more as a starting point for new ports.
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */
#ifndef __ASM_GENERIC_SYSTEM_H
#define __ASM_GENERIC_SYSTEM_H

#ifdef __KERNEL__
#ifndef __ASSEMBLY__

#include <linux/types.h>
#include <linux/irqflags.h>

#include <asm/cmpxchg-local.h>
#include <asm/cmpxchg.h>

struct task_struct;

/* context switching is now performed out-of-line in switch_to.S */
extern struct task_struct *__switch_to(struct task_struct *,
		struct task_struct *);
#define switch_to(prev, next, last)					\
	do {								\
		((last) = __switch_to((prev), (next)));			\
	} while (0)

#define arch_align_stack(x) (x)

#define nop() asm volatile ("nop")

#endif /* !__ASSEMBLY__ */

/*
 * Force strict CPU ordering.
 * And yes, this is required on UP too when we're talking
 * to devices.
 *
 * This implementation only contains a compiler barrier.
 */

#define mb()	asm volatile ("": : :"memory")
#define rmb()	mb()
#define wmb()	asm volatile ("": : :"memory")

#ifdef CONFIG_SMP
#define smp_mb()	mb()
#define smp_rmb()	rmb()
#define smp_wmb()	wmb()
#else
#define smp_mb()	barrier()
#define smp_rmb()	barrier()
#define smp_wmb()	barrier()
#endif

#define set_mb(var, value)  do { var = value;  mb(); } while (0)
#define set_wmb(var, value) do { var = value; wmb(); } while (0)

#define read_barrier_depends()		do {} while (0)
#define smp_read_barrier_depends()	do {} while (0)

/*
 * we make sure local_irq_enable() doesn't cause priority inversion
 */
#ifndef __ASSEMBLY__

/* This function doesn't exist, so you'll get a linker error
 *    if something tries to do an invalid xchg().  */
extern void __xchg_called_with_bad_pointer(void);

static inline
unsigned long __xchg(unsigned long x, volatile void *ptr, int size)
{
	unsigned long ret, flags;

	switch (size) {
	case 1:
#ifdef __xchg_u8
		return __xchg_u8(x, ptr);
#else
		local_irq_save(flags);
		ret = *(volatile u8 *)ptr;
		*(volatile u8 *)ptr = x;
		local_irq_restore(flags);
		return ret;
#endif /* __xchg_u8 */

	case 2:
#ifdef __xchg_u16
		return __xchg_u16(x, ptr);
#else
		local_irq_save(flags);
		ret = *(volatile u16 *)ptr;
		*(volatile u16 *)ptr = x;
		local_irq_restore(flags);
		return ret;
#endif /* __xchg_u16 */

	case 4:
#ifdef __xchg_u32
		return __xchg_u32(x, ptr);
#else
		local_irq_save(flags);
		ret = *(volatile u32 *)ptr;
		*(volatile u32 *)ptr = x;
		local_irq_restore(flags);
		return ret;
#endif /* __xchg_u32 */

#ifdef CONFIG_64BIT
	case 8:
#ifdef __xchg_u64
		return __xchg_u64(x, ptr);
#else
		local_irq_save(flags);
		ret = *(volatile u64 *)ptr;
		*(volatile u64 *)ptr = x;
		local_irq_restore(flags);
		return ret;
#endif /* __xchg_u64 */
#endif /* CONFIG_64BIT */

	default:
		__xchg_called_with_bad_pointer();
		return x;
	}
}

#define xchg(ptr, x) \
	((__typeof__(*(ptr))) __xchg((unsigned long)(x), (ptr), sizeof(*(ptr))))

#endif /* !__ASSEMBLY__ */

#endif /* __KERNEL__ */
#endif /* __ASM_GENERIC_SYSTEM_H */