S3C6410使用---38关于mem_map

一. Unable to handle kernel paging request at virtual address
移植LCD驱动,会出现如下的错误:
Unable to handle kernel paging request at virtual address 0xf7100130
定位一下发现是在drviers/video/samsun/s3cfb_fimd4x.c中,一调用writel就会报错

void s3cfb_pre_init(void)
{
    s3cfb_fimd.vidintcon0 &= ~S3C_VIDINTCON0_FRAMESEL0_MASK;
    s3cfb_fimd.vidintcon0 |= S3C_VIDINTCON0_FRAMESEL0_VSYNC;
    s3cfb_fimd.vidintcon0 |= S3C_VIDINTCON0_INTFRMEN_ENABLE;
    //打印dbmsg("S3C_VIDINTCON0=0x%x",S3C_VIDINTCON0);
    writel(s3cfb_fimd.vidintcon0, S3C_VIDINTCON0);
}

同时打印S3C_VIDINTCON0的值正好是0xf7100130,
也就是说0xf7100130这个虚拟地址没有与io端口相关联.
查找开发板自带的内核发现是在arch/arm/mach-s3c64xx/mach-smdk6410.c中,
添加了如下定义:

static struct map_desc smdk6410_iodesc[] = {
    {
        .virtual = (unsigned long)S3C_VA_LCD,   //0x
        .pfn = __phys_to_pfn(S3C_PA_FB),
        .length = SZ_16K,
        .type = MT_DEVICE,
    },
};

那么这段代码有什么作用呢?
二. IO端口映射
用到smdk6410_iodesc的是:
在arch/arm/mach-s3c64xx/mach-smdk6410.c中

static void __init smdk6410_map_io(void)
{
    //映射 IRQ SYS MEM　TIMER WATCHDOG UART LCD
    s3c64xx_init_io(smdk6410_iodesc, ARRAY_SIZE(smdk6410_iodesc));
}

在arch/arm/mach-s3c64xx/cpu.c中

void __init s3c64xx_init_io(struct map_desc *mach_desc, int size)
{
    unsigned long idcode;
    //下面这一行映射 IRQ SYS MEM　TIMER WATCHDOG UART
    iotable_init(s3c_iodesc, ARRAY_SIZE(s3c_iodesc));
    //下面这一行只映射LCD
    iotable_init(mach_desc, size);      //下面就以LCD为例说一下

    idcode = __raw_readl(S3C_VA_SYS + 0x118);
    if (!idcode) {
        __raw_writel(0x0, S3C_VA_SYS + 0xA1C);
        idcode = __raw_readl(S3C_VA_SYS + 0xA1C);
    }

    s3c_init_cpu(idcode, cpu_ids, ARRAY_SIZE(cpu_ids));
}

在arch/arm/mm/mmu.c中

void __init iotable_init(struct map_desc *io_desc, int nr)
{
    //LCD的map_desc只有一项,所以这个nr=1
    for (i = 0; i < nr; i++)
        create_mapping(io_desc + i);
}

在arch/arm/mm/mmu.c中

static void __init create_mapping(struct map_desc *md)
{
    unsigned long addr, length, end;
    phys_addr_t phys;
    const struct mem_type *type;
    pgd_t *pgd;

    if (md->virtual != vectors_base() && md->virtual < TASK_SIZE)
        return;

    if ((md->type == MT_DEVICE || md->type == MT_ROM) &&
        md->virtual >= PAGE_OFFSET && md->virtual < VMALLOC_END) {
    }

    type = &mem_types[md->type];
    //页帧地址>0x100000,即实际的物理地址>0x100000000=4G, 大于4G的物理地址,现在不适合
    if (md->pfn >= 0x100000) {
        create_36bit_mapping(md, type);
        return;
    }

    addr = md->virtual & PAGE_MASK;
    phys = __pfn_to_phys(md->pfn);
    length = PAGE_ALIGN(md->length + (md->virtual & ~PAGE_MASK));

    if (type->prot_l1 == 0 && ((addr | phys | length) & ~SECTION_MASK)) {
        return;
    }

    pgd = pgd_offset_k(addr);
    end = addr + length;
    do {
        unsigned long next = pgd_addr_end(addr, end);
        alloc_init_pud(pgd, addr, next, phys, type);
        phys += next - addr;
        addr = next;
    } while (pgd++, addr != end);
}

内存映射在内核启动时就会去映射,并且早于驱动的加载,如果没有映射端口就在驱动中使用了虚拟地址就会报上面的错误.

http://blog.chinaunix.net/uid-26009923-id-3860465.html