linux 驱动寄存器读写

linux  driver write   writel_relaxed

readb()和writeb()系列函数

 1 #define readb_relaxed(c) ({ u8  __r = __raw_readb(c); __r; })
 2 #define readw_relaxed(c) ({ u16 __r = le16_to_cpu((__force __le16) \
 3                     __raw_readw(c)); __r; })
 4 #define readl_relaxed(c) ({ u32 __r = le32_to_cpu((__force __le32) \
 5                     __raw_readl(c)); __r; })
 6 
 7 #define writeb_relaxed(v,c)    __raw_writeb(v,c)
 8 #define writew_relaxed(v,c)    __raw_writew((__force u16) cpu_to_le16(v),c)
 9 #define writel_relaxed(v,c)    __raw_writel((__force u32) cpu_to_le32(v),c)
10 
11 #define readb(c)        ({ u8  __v = readb_relaxed(c); __iormb(); __v; })
12 #define readw(c)        ({ u16 __v = readw_relaxed(c); __iormb(); __v; })
13 #define readl(c)        ({ u32 __v = readl_relaxed(c); __iormb(); __v; })
14 
15 #define writeb(v,c)        ({ __iowmb(); writeb_relaxed(v,c); })
16 #define writew(v,c)        ({ __iowmb(); writew_relaxed(v,c); })
17 #define writel(v,c)        ({ __iowmb(); writel_relaxed(v,c); })

此系列函数用于从内存映射的I/O空间读写数据

readb()和readb_relaxed()从I/O空间读取8位数据(1字节)

readw()和readb_relaxew()从I/O空间读取16位数据(2字节)

readl()和readb_relaxel()从I/O空间读取32位数据(4字节)

writeb()和writeb_relaxed()从I/O空间写入8位数据(1字节)

writew()和writew_relaxed()从I/O空间写入16位数据(2字节)

writel()和writel_relaxed()从I/O空间写入32位数据(4字节)

其中没有relaxed()的系列函数都调用了__iowmb()和__iormb()函数，这两个函数是内存屏障指令，防止编译器优化执行过程。

 访问物理地址

 u32 vaddr, i;

 vaddr = (u32)phys_to_virt(in_be32(&bd->buf));