Hi , All !
I am porting a linux driver for PCI device and some applications form x86
platform to AMD Au1550 MIPS , running MontaVista Linux 2.4.20-mvl31.1550.
I got the following problem :
The driver allocates some memory (SharedMemory) for communication with PCI
card , using function pci_alloc_consistent(). PCI card can write to this
memory using DMA . On kernel level driver correctly reads values, written
by the board , and the board correctly reads values, written by driver.
The goal is to make this memoty visible from user level application. The
following approach is used on õ86 and works :
1. Application calls mmap( 0, Size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0
2. driver implements mmap() function that just prepares some vma
structure fields for nopage operetions :
vma->vm_flags |= VM_RESERVED; // no swapping
vma->vm_ops = &device_vmops; // contains nopage func
vma->vm_file = filp;
3. Application gets pointer and accesses all mapped pages (reads a byte
from each page) - this causes call of nopage function in driver .
The nopage function calculates VirtualAddress from SharedMemory address
(received after pci_alloc_consistent()),
then does KernelPage= virt_to_page(VirtualAddress) ,
and returns KernelPage.
4. Now Application reads from SharedMemory , using a pointer , given by
This works fine on x86 platform , but on MIPS application cannot see
expected contents of the memory - it reads garbage .
What I have tried :
- to insert vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot)
in driver?s implementation of mmap() ;
- to use remap_page_range() instead of vm_ops .
Result is the same ? application reads garbage . If application write some
values into the memory - it reads garbage . The values written by
application are not seen from kernel level .
I am new to MIPS so maybe I missed something obvious ? Is this right
approach on this platform at all ?
Thank you in advance!
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