Direct physcial register access (I/O)
 

I would like make some "UART" like I/O device driver read/write/interrupt
path is just I/O(like UART) (not dma, pci,i2c)

my device base address is 0xdff00000
and some of register offset are 0x04,0x08 etc.....

if I want to access this register , how can I do that?

#define dev_base 0xdff00000
#define dev_reg1 dev_base+0x04
#define dev_reg2 dev_base+0x08

regwrite example

*(unsigned char*)dev_reg1 = 0xFF
*(unsigned char*)dev_reg1 = 0xFF

read example
int read_val=0
read_val= *(unsigned char*)dev_reg1;
printk("===>reg value is %x\n",read_val);



I think it has very critical problems.
How can I access this registers on linux....

after search some file, but I couldn't understand.....

What space do you want to access those registers, in kernel or user space?

In kernel space, how it is possible?

You can access those register in kernel space like regular memory after calling ioremap.

ioremap
 

Since your device is memory mapped IO, it is better to use "ioremap_nocache". Always check for the return status of the function "request_mem_region" before remapping the memory. If both the functions passed, then your mapped memory will be visible in /proc/iomem.

In summary, understanding some kernel functions like below will be helpful
1. request_mem_region
2. ioremap_nocache
3. iounmap
4. release_mem_region

Best regards,
Suresh Maniyath

Thank You Very Much