驱动层ioremap创建页表流程

驱动层ioremap创建页表流程

在编写linux设备驱动程序时经常使用ioremap接口将外设的物理地址转换成虚拟地址，继而通过访问内存的方式来访问外设物理地址

空间的内容。下来就详细看下ioremap的具体流程。在ARM上，ioremap相关的操作api如下：

#define ioremap(cookie,size) __arm_ioremap((cookie), (size), MT_DEVICE)

#define ioremap_nocache(cookie,size) __arm_ioremap((cookie), (size), MT_DEVICE)

#define ioremap_cached(cookie,size) __arm_ioremap((cookie), (size), MT_DEVICE_CACHED)

#define ioremap_wc(cookie,size) __arm_ioremap((cookie), (size), MT_DEVICE_WC)

#define iounmap __arm_iounmap

}

查看arch_ioremap_caller后发现其是一个函数指针，具体指向的函数如下：

void __iomem * (*arch_ioremap_caller)(unsigned long, size_t, unsigned int, void *) = __arm_ioremap_caller;

void __iomem *__arm_ioremap_caller(unsigned long phys_addr, size_t size, unsigned int mtype, void *caller)

{

unsigned long last_addr;

unsigned long offset = phys_addr & ~PAGE_MASK;

unsigned long pfn = __phys_to_pfn(phys_addr);

/*

* Don't allow wraparound or zero size

上述函数首先根据物理地址计算出offset（物理地址的低12位地址），再计算出pfn，然后调用__arm_ioremap_pfn_caller，如下：

void __iomem * __arm_ioremap_pfn_caller(unsigned long pfn, unsigned long offset, size_t size, unsigned int mtype, void *caller)

{

const struct mem_type *type;

int err;

unsigned long addr;

struct vm_struct * area;

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type = get_mem_type(mtype);

if (!type)

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/*

* Try to reuse one of the static mapping whenever possible.

*/

read_lock(&vmlist_lock);

for (area = vmlist; area; area = area->next) {

if (!size || (sizeof(phys_addr_t) == 4 && pfn >= 0x100000))

break;

if (!(area->flags & VM_ARM_STATIC_MAPPING))

continue;

read_unlock(&vmlist_lock);

addr = (unsigned long)area->addr;

addr += __pfn_to_phys(pfn) - area->phys_addr;

return (void __iomem *) (offset + addr);

}

read_unlock(&vmlist_lock);

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/*

* Don't allow RAM to be mapped - this causes problems with ARMv6+

*/