In my embedded board there is a alphanumeric display.It is 5 bytes in size. We are using linux-2.6.25 kernel.
Now i am accessing the memory in my kernel driver like below.

DISP_ADDR 0xfB80020

unsigned short *disp_base;
if(!disp_base =ioremap(DISP_ADDR, 0x05)
{
printk("ioremap fialed");return -1;
}

It is working fine. i am using disp_base in further part of dirver for accessing. Now i want to remap this to userspace. So that i can directly access form the userspace. Please help me out. I only now that in the file operations i have to write mmap function. Please help me how to write this mmap function in detail. I am new to this linux.

The book has a good example, Linux Device Drivers: http://lwn.net/Kernel/LDD3/.

i have gone through the book, i implemented like this in kernel

int disp_mmap(struct file *file, struct vm_area_struct *vma)
{
if(remap_pfn_range(vma,vma->vm_start,DISP_ADDR >>PAGE_SHIFT,0x05,vma->vm_page_prot))
return -EAGAIN;
return 0;
}

in usermode i tried to access the pointer like this

map_buff=mmap(0,0x05,PROT_READ| PROT_WRITE, MAP_FILE|MAP_SHARED,disp_fd,0);

i am getting the error as below.

"Unable to handle kernel access at virtual address 0xc756804b"

Please help me out

You should read section, Remapping Specific I/O Regions, again. The remap_pfn_range parameter is wrong.

in the remap_pfn_range,function
remap_pfn_range(vma,vma->vm_start,DISP_ADDR >>PAGE_SHIFT,0x05,vma->vm_page_prot)

I think problem may be in physical address parameter.
Can you please point out which paremeter is represented wrongly.

thanks and regards
babu

I copied and pasted some example code from book.


The following does the trick for a driver mapping a region of simple_region_size bytes, beginning at physical address simple_region_start (which should be page-aligned):

unsigned long off = vma->vm_pgoff << PAGE_SHIFT;
unsigned long physical = simple_region_start + off;
unsigned long vsize = vma->vm_end - vma->vm_start;
unsigned long psize = simple_region_size - off;

if (vsize > psize)
return -EINVAL; /* spans too high */
remap_pfn_range(vma, vma_>vm_start, physical, vsize, vma->vm_page_prot);