IO端口與IO內(nèi)存的概念：外設(shè)中的寄存器稱為是IO端口，外設(shè)中的內(nèi)存稱為是IO內(nèi)存。二者統(tǒng)稱為IO空間。Linux內(nèi)核是通過虛擬地址訪問外設(shè)的。所以需要先將虛擬地址映射到相應(yīng)外設(shè)的物理地址上，linux的映射方式有兩種：靜態(tài)映射(map_desc)和動態(tài)映射(ioremap)，其實(shí)也是內(nèi)核訪問外設(shè)資源的方式。

在驅(qū)動中配置寄存器，可以調(diào)用類似于s3c_gpio_cfgpin、s3c_gpio_setpull、gpio_direction_output等直接配置IO寄存器的函數(shù)。這些函數(shù)訪問的虛擬地址，這些虛擬地址都是已經(jīng)在啟動啟動的時(shí)候通過靜態(tài)映射方式映射到IO寄存器的物理地址上。

靜態(tài)映射概念：所謂的靜態(tài)映射是指，虛擬地址到物理地址的轉(zhuǎn)換所需要的頁表在操作系統(tǒng)啟動時(shí)已經(jīng)配置好，不需要用戶進(jìn)行配置，虛擬地址到物理地址的查表轉(zhuǎn)換可直接完成(fromnet)。

以s5pv210為例講述：

MACHINE_START(SMDKV210,"SMDKV210")

/* Maintainer: Kukjin Kim */

.boot_params =S5P_PA_SDRAM + 0x100,

.init_irq =s5pv210_init_irq,

.map_io = smdkv210_map_io,

.init_machine = smdkv210_machine_init,

#ifdefCONFIG_S5P_HIGH_RES_TIMERS

.timer = &s5p_systimer,

#else

.timer =&s5p_timer,

#endif

MACHINE_END

其中IO映射函數(shù)是smdkv210_map_io實(shí)現(xiàn)：

staticvoid __init smdkv210_map_io(void)

{

s5p_init_io(NULL,0, S5P_VA_CHIPID);

s3c24xx_init_clocks(24000000);

s5pv210_gpiolib_init();

s3c24xx_init_uarts(smdkv210_uartcfgs,

ARRAY_SIZE(smdkv210_uartcfgs));

#ifndefCONFIG_S5P_HIGH_RES_TIMERS

s5p_set_timer_source(S5P_PWM2, S5P_PWM4);

#endif

s5p_reserve_bootmem(s5pv210_media_devs,

ARRAY_SIZE(s5pv210_media_devs),

S5P_RANGE_MFC);

}

該函數(shù)中調(diào)用s5p_init_io進(jìn)行地址的映射，

/*read cpu identification code */

void__inits5p_init_io(struct map_desc*mach_desc,

int size, void __iomem *cpuid_addr)

{

unsigned long idcode;

/* initialize the io descriptors we need forinitialization */

iotable_init(s5p_iodesc, ARRAY_SIZE(s5p_iodesc));

if (mach_desc)

iotable_init(mach_desc, size);

idcode = __raw_readl(cpuid_addr);

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

}

其中最重要是struct map_desc s5p_iodesc[]結(jié)構(gòu)體 和 staticstruct map_desc s5pv210_iodesc[]：

structmap_desc{

unsigned long virtual; // IO空間映射后的虛擬地址

unsigned long pfn; // IO空間的物理地址所在的頁幀號

unsigned long length; // IO空間的長度

unsigned int type; // IO空間的類型

};

/*minimal IO mapping這部分是最小系統(tǒng)層次的映射*/

staticstruct map_desc s5p_iodesc[] __initdata = {

{

.virtual =(unsigned long)S5P_VA_CHIPID,

.pfn =__phys_to_pfn(S5P_PA_CHIPID),

.length =SZ_4K,

.type =MT_DEVICE,

}, {

.virtual = (unsigned long)S3C_VA_SYS,

.pfn = __phys_to_pfn(S5P_PA_SYSCON),

.length = SZ_64K,

.type = MT_DEVICE,

},{

.virtual =(unsigned long)S3C_VA_TIMER,

.pfn =__phys_to_pfn(S5P_PA_TIMER),

.length =SZ_16K,

.type =MT_DEVICE,

},{

.virtual =(unsigned long)S3C_VA_WATCHDOG,

.pfn =__phys_to_pfn(S3C_PA_WDT),

.length =SZ_4K,

.type =MT_DEVICE,

}, {

.virtual =(unsigned long)S5P_VA_SROMC,

.pfn =__phys_to_pfn(S5P_PA_SROMC),

.length =SZ_4K,

.type =MT_DEVICE,

},

};

/*Initial IO mappings*/

staticstruct map_desc s5pv210_iodesc[] __initdata = {

{

.virtual =(unsigned long)S5P_VA_SYSTIMER,

.pfn =__phys_to_pfn(S5PV210_PA_SYSTIMER),

.length =SZ_4K,

.type =MT_DEVICE,

}, {

.virtual =(unsigned long)S5P_VA_GPIO,

.pfn =__phys_to_pfn(S5PV210_PA_GPIO),

.length =SZ_4K,

.type =MT_DEVICE,

}, {

.virtual =(unsigned long)VA_VIC0,

.pfn =__phys_to_pfn(S5PV210_PA_VIC0),

.length =SZ_16K,

.type =MT_DEVICE,

}, {

.virtual =(unsigned long)VA_VIC1,

.pfn =__phys_to_pfn(S5PV210_PA_VIC1),

.length =SZ_16K,

.type =MT_DEVICE,

}, {

.virtual =(unsigned long)VA_VIC2,

.pfn =__phys_to_pfn(S5PV210_PA_VIC2),

.length =SZ_16K,

.type =MT_DEVICE,

}, {

.virtual =(unsigned long)VA_VIC3,

.pfn =__phys_to_pfn(S5PV210_PA_VIC3),

.length =SZ_16K,

.type =MT_DEVICE,

}, {

.virtual =(unsigned long)S3C_VA_UART,

.pfn =__phys_to_pfn(S3C_PA_UART),

.length =SZ_512K,

.type =MT_DEVICE,

}, {

.virtual =(unsigned long)S5P_VA_DMC0,

.pfn =__phys_to_pfn(S5PV210_PA_DMC0),

.length =SZ_4K,

.type =MT_DEVICE,

}, {

.virtual =(unsigned long)S5P_VA_DMC1,

.pfn =__phys_to_pfn(S5PV210_PA_DMC1),

.length =SZ_4K,

.type =MT_DEVICE,

},{

.virtual = (unsigned long)S5P_VA_BUS_AXI_DSYS,

.pfn = __phys_to_pfn(S5PV210_PA_BUS_AXI_DSYS),

.length= SZ_4K,

.type = MT_DEVICE,