I have build an character driver in which i am allocating two PAGESIZE buffer using dma_alloc_coherent

Now i am passing the PHYSICAL address of these BUFFER
[src_ptr & dest_ptr] to user space using IOCTL as source_offset and dest_offset .

In user space this offeset is used as an offset for mmap call.
So on same /dev file say /dev/250 i am making TWO MMAP call

usr_src_ptr= mmap(0,page_size, PROT_READ|PROT_WRITE,MAP_SHARED, dev_FD,src_offset );
if (usr_src_ptr == MAP_FAILED){
printf("USR[UPP]:SOURCE MMAP FAiled \n\n");
close(dev_FD);
exit(-1);
}else{
printf("USR[UPP]:SOURCE MMAP is %X..\n",usr_src_ptr);
}

usr_dest_ptr= mmap(0,page_size, PROT_READ|PROT_WRITE,MAP_SHARED,dev_FD,dest_offset );

if (usr_dest_ptr == MAP_FAILED){
printf("USR[UPP]DEST MMAP FAiled \n\n");
close(dev_FD);
exit(-1);
}else{
printf("USR[UPP]DEST MMAP is %X..\n",usr_dest_ptr);
}


1. I am writing 0x77 in user_src_ptr in user space & printing
user_src_ptr in user space and dest_src_ptr in KERNEL space .
I get correct data for both user and kernel space

2. I am writng 0x55 in dest_ptr in kernel space & printing dest_ptr
in kernel space and usr_dest_ptr in user space.
NOW FOR THIS CASE I GET CORRECT DATA I.E 0X55 IN KERNEL BUFFER
dest_ptR , BUT THE USER SPACE BUFFER OF DESTINATION ALWAYS
RETURNS 0X77 . i.e THE DATA WHICH I HAVE WRITTEN IN usr_src_ptr.


Can any one please let me know if we can do TWO MMAP operation on same file at different OFFSET ?????

Thank You Ashish Mishra

The issue was with :-
if ((ret = remap_pfn_range(vma,vma->vm_start,
(virt_to_phys((void *)src_ptr) >> PAGE_SHIFT),
size,vma->vm_page_prot)) < 0)
{
return ret;
}

Due to this ir-respective of offset , i was getting mapped to same PHYSICAL address

You are doing it wrong. Why are you passing physical address to user space? Why does user space need to know it?

Of course.

Mina86 ,
Actually i wanted to do an mmap of two kernel buffer of my character driver.
So on single /dev file i am doing an mmap of two buffer .
To distinguish these buffer i am using PHYSICAL address of both buffer as an OFFSET parameter from user space .

IS THIS MECHANISM CORRECT !!!!!!!!!!!!!