在linux内核中映射io设备地址？

Question

printk(" start = %p , end = %p \n",res->start ,res->end );
fbi->reg_base = ioremap_nocache(res->start, res->end - res->start);
printk(" fbi->reg_base = %p \n",fbi->reg_base);
printk(" virt_to_phys(fbi->reg_base) = %p \n", virt_to_phys(fbi->reg_base));
printk(" virt_to_bus(fbi->reg_base) = %p \n", virt_to_bus(fbi->reg_base));

输出为

start = 72100000 , end = 72100fff 
fbi->reg_base = 70b10000
virt_to_phys(fbi->reg_base) = a0b10000
virt_to_phys(fbi->reg_base) = a0b10000

为什么我不能拿回0x72100000？

Answer 1

我想你不会得到那个地址，因为ioremap_nocache返回的地址不能保证是一个虚拟地址，因为它说的是here

ioremap_nocache执行特定于平台的操作序列，使总线内存CPU可通过readb/readw/readl/writeb/ writew/writel函数和其他mmio进行访问。不能保证返回的地址可以直接用作虚拟地址。