什么是I/O内存？

//申请IO内存/*start: 该IO的地址相当与物理地址n: 申请IO数量，必须是start起始地址连续 len个字节nane: 设备名称或者IO端口名称，用以标记该端口被谁使用*/#define request_mem_region(start,n,name) \__request_region(&iomem_resource, (start), (n), (name), 0)#define devm_request_mem_region(dev,start,n,name) \__devm_request_region(dev, &iomem_resource, (start), (n), (name))//释放IO内存#define release_mem_region(start,n)  \__release_region(&iomem_resource, (start), (n)) #define devm_release_mem_region(dev, start, n) \__devm_release_region(dev, &iomem_resource, (start), (n))

//将物理地址映射为虚拟地址void__iomem*ioremap(unsignedlongphys_addr, unsignedlongsize)
void__iomem*devm_ioremap(structdevice*dev, resource_size_toffset,
unsignedlongsize)
//申请IO内存并进行重映射(将物理地址映射为虚拟地址)//它对devm_request_mem_region()和devm_ioremap()进行了封装，内部会调用这两个函数  void__iomem*devm_ioremap_resource(structdevice*dev, structresource*res)
//对设备内存映射的虚拟地址进行读写//读8bit , 16bit, 32bit#define readb(c)         ({ u8  __v = readb_relaxed(c); __iormb(); __v; })#define readw(c)         ({ u16__v = readw_relaxed(c); __iormb(); __v; })#define readl(c)        ({ u32 __v = readl_relaxed(c); __iormb(); __v; })//写8bit , 16bit, 32bit#define writeb(v,c)         ({ __iowmb(); writeb_relaxed(v,c); })#define writew(v,c)         ({ __iowmb(); writew_relaxed(v,c); })#define writel(v,c)         ({ __iowmb(); writel_relaxed(v,c); })