readX/writeX() are used to access memory mapped devices. On some
* architectures the memory mapped IO stuff needs to be accessed
* differently. On the simple architectures, we just read/write the
* memory location directly.
writel() 往内存映射的 I/O 空间上写数据，wirtel() I/O 上写入 32 位数据 (4字节)。
原型：
#include
void writel (unsigned char data , unsigned short addr )
readl() 从内存映射的 I/O 空间读取数据,readl 从 I/O 读取 32 位数据 ( 4 字节 )。
原型：
#include
unsigned char readl (unsigned int addr )
变量 addr 是 I/O 地址。
返回值 ： 从 I/O 空间读取的数值。
定义
#define readb __raw_readb
#define readw(addr) __le16_to_cpu(__raw_readw(addr))
#define readl(addr) __le32_to_cpu(__raw_readl(addr))
#ifndef __raw_readb
staTIc inline u8 __raw_readb(const volaTIle void __iomem *addr)
{
return *(const volaTIle u8 __force *) addr;
}
#endif
#ifndef __raw_readw
staTIc inline u16 __raw_readw(const volatile void __iomem *addr)
{
return *(const volatile u16 __force *) addr;
}
#endif
#ifndef __raw_readl
static inline u32 __raw_readl(const volatile void __iomem *addr)
{
return *(const volatile u32 __force *) addr;
}
#endif
#define writeb __raw_writeb
#define writew(b,addr) __raw_writew(__cpu_to_le16(b),addr)
#define writel(b,addr) __raw_writel(__cpu_to_le32(b),addr)
