ARM Linux下的phys_to_virt/virt_to_phys函数

1）phys_to_virt/virt_to_phys函数定义

arch/arm/include/asm/memory.h

131 #ifndef __virt_to_phys132 #define __virt_to_phys(x)       ((x) - PAGE_OFFSET + PHYS_OFFSET)133 #define __phys_to_virt(x)       ((x) - PHYS_OFFSET + PAGE_OFFSET)134 #endif

182 static inline unsigned long virt_to_phys(void *x)183 {184         return __virt_to_phys((unsigned long)(x));185 }186 187 static inline void *phys_to_virt(unsigned long x)188 {189         return (void *)(__phys_to_virt((unsigned long)(x)));190 }

 

2）PAGE_OFFSET/PHYS_OFFSET两个宏的定义

PHYS_OFFSET宏，通常在特定的板子的memory.h文件种定义，对应的物理内存的地址。而PAGE_OFFSET其实就是虚拟地址的起始地址。在arch/arm/include/asm/memory.h文件中定义，默认值为0xC0000000。

#ifdef CONFIG_MMU

/*
 * PAGE_OFFSET - the virtual address of the start of the kernel image
 * TASK_SIZE - the maximum size of a user space task.
 * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area
 */
#define PAGE_OFFSET        UL(CONFIG_PAGE_OFFSET)
#define TASK_SIZE        (UL(CONFIG_PAGE_OFFSET) - UL(0x01000000))
#define TASK_UNMAPPED_BASE    (UL(CONFIG_PAGE_OFFSET) / 3)

/*
 * The maximum size of a 26-bit user space task.
 */
#define TASK_SIZE_26        UL(0x04000000)

......
......
#else /* CONFIG_MMU */

/*
 * The limitation of user task size can grow up to the end of free ram region.
 * It is difficult to define and perhaps will never meet the original meaning
 * of this define that was meant to.
 * Fortunately, there is no reference for this in noMMU mode, for now.
 */
#ifndef TASK_SIZE
#define TASK_SIZE        (CONFIG_DRAM_SIZE)
#endif

#ifndef TASK_UNMAPPED_BASE
#define TASK_UNMAPPED_BASE    UL(0x00000000)
#endif

#ifndef PHYS_OFFSET
#define PHYS_OFFSET         UL(CONFIG_DRAM_BASE)
#endif


......
......
#endif /* !CONFIG_MMU */

 

arch/arm/Kconfig

1165 config PAGE_OFFSET   ----这个就是CONFIG_PAGE_OFFSET宏，默认值为0xC0000000
1166 hex
1167 default 0x40000000 if VMSPLIT_1G
1168 default 0x80000000 if VMSPLIT_2G
1169 default 0xC0000000