linux驱动2--ioremap过程

TQ2440的watchdog linux驱动在内核源码linux-2.6.30.4的:  ./drivers/watchdog/s3c2410_wdt.c下

1. watchdog ioremap的过程:

res->start=0x53000000   //物理地址

wdt_base=0xc5400000 //虚拟地址

wdt_base = ioremap(res->start, size);

将物理地址res->start映射到了虚拟地址0xc5400000处，映射大小为:size=0x100000.

注： 不知道为什么刚开始这个size=8,后来就成了0x100000(1M)。

2. arch/arm/include/asm/io.h中,找到ioremap的定义:

//出现两个ioremap
#ifndef __arch_ioremap
#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(cookie)            __iounmap(cookie)
#else
#define ioremap(cookie,size)        __arch_ioremap((cookie), (size), MT_DEVICE)
#define ioremap_nocache(cookie,size)    __arch_ioremap((cookie), (size), MT_DEVICE)
#define ioremap_cached(cookie,size)    __arch_ioremap((cookie), (size), MT_DEVICE_CACHED)
#define ioremap_wc(cookie,size)        __arch_ioremap((cookie), (size), MT_DEVICE_WC)
#define iounmap(cookie)            __arch_iounmap(cookie)
#endif

没有定义 #ifndef __arch_ioremap，所以是
#define MT_DEVICE        0
#define ioremap(cookie,size)        __arm_ioremap(cookie, size, MT_DEVICE)

3.在arch/arm/mm/ioremap.c中

__arm_ioremap(cookie, size, MT_DEVICE) 也有两个定义，一个是在nommu.c中，一个是在arch/arm/mm/ioremap.c中，所以很明显进入 arch/arm/mm/ioremap.c中：
//这个函数将物理地址phys_addr拆成两部分高20位的页帧号(Page Frame Number)pfn和低12位的页内偏移地址offset
void __iomem *
__arm_ioremap(unsigned long phys_addr, size_t size, unsigned int mtype)
{
    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
     */
    last_addr = phys_addr + size - 1;
    if (!size || last_addr < phys_addr)
        return NULL;
     //此处打印值如下: last_addr=0x530fffff, size=0x100000, offset=0x0, pfn=0x53000
     return __arm_ioremap_pfn(pfn, offset, size, mtype);
}
EXPORT_SYMBOL(__arm_ioremap);

/*
 * Convert a physical address to a Page Frame Number and back
 */
#define PAGE_SHIFT        12
#define    __phys_to_pfn(paddr)    ((paddr) >> PAGE_SHIFT)

4. 在arch/arm/mm/ioremap.c中

/*
 * Remap an arbitrary physical address space into the kernel virtual
 * address space. Needed when the kernel wants to access high addresses
 * directly.
 *
 * We need to allow non-page-aligned mappings too: we will obviously
 * have to convert them into an offset in a page-aligned mapping, but the
 * caller shouldn't need to know that small detail.
 *
 * 'flags' are the extra L_PTE_ flags that you want to specify for this
 * mapping. See <asm/pgtable.h> for more information.
 */
void __iomem *
__arm_ioremap_pfn(unsigned long pfn, unsigned long offset, size_t size,
          unsigned int mtype)
{
    const struct mem_type *type;
    int err;
    unsigned long addr;
     struct vm_struct * area;

    /*
     * High mappings must be supersection aligned
     */
    if (pfn >= 0x100000 && (__pfn_to_phys(pfn) & ~SUPERSECTION_MASK))
        return NULL;

    type = get_mem_type(mtype);
    if (!type)
        return NULL;

    /*
     * Page align the mapping size, taking account of any offset.
     */
    size = PAGE_ALIGN(offset + size);

     area = get_vm_area(size, VM_IOREMAP); //分配虚拟地址空间
     if (!area)
         return NULL;
     addr = (unsigned long)area->addr;
     //此处打印出的地址: addr=0xc5400000
#ifndef CONFIG_SMP //不进入此处
    if (DOMAIN_IO == 0 &&
        (((cpu_architecture() >= CPU_ARCH_ARMv6) && (get_cr() & CR_XP)) ||
           cpu_is_xsc3()) && pfn >= 0x100000 &&
           !((__pfn_to_phys(pfn) | size | addr) & ~SUPERSECTION_MASK)) {
        area->flags |= VM_ARM_SECTION_MAPPING;
        err = remap_area_supersections(addr, pfn, size, type);
    } else if (!((__pfn_to_phys(pfn) | size | addr) & ~PMD_MASK)) {
        area->flags |= VM_ARM_SECTION_MAPPING;
        err = remap_area_sections(addr, pfn, size, type);
    } else
#endif
        err = remap_area_pages(addr, pfn, size, type);

    if (err) {
         vunmap((void *)addr);
         return NULL;
     }

    flush_cache_vmap(addr, addr + size);
    return (void __iomem *) (offset + addr);
}
EXPORT_SYMBOL(__arm_ioremap_pfn);

area = get_vm_area(size, VM_IOREMAP); //分配虚拟地址空间

err = remap_area_pages(addr, pfn, size, type);

这两个函数。

5. 在arch/arm/mm/ioremap.c中

static int
remap_area_sections(unsigned long virt, unsigned long pfn,
            size_t size, const struct mem_type *type)
{
    unsigned long addr = virt, end = virt + size;
    pgd_t *pgd;

    /*
     * Remove and free any PTE-based mapping, and
     * sync the current kernel mapping.
     */
    unmap_area_sections(virt, size);

    pgd = pgd_offset_k(addr);
    do {
        pmd_t *pmd = pmd_offset(pgd, addr);

        pmd[0] = __pmd(__pfn_to_phys(pfn) | type->prot_sect);
        pfn += SZ_1M >> PAGE_SHIFT;
        pmd[1] = __pmd(__pfn_to_phys(pfn) | type->prot_sect);
        pfn += SZ_1M >> PAGE_SHIFT;
        flush_pmd_entry(pmd);

        addr += PGDIR_SIZE;
        pgd++;
    } while (addr < end);

    return 0;
}