On Thu, May 19, 2011 at 12:14:40AM +0200, Leon Woestenberg wrote:
> Hello,
>
> I cannot get my driver's mmap() to work. I allocate 64 KiB ringbuffer
> using pci_alloc_consistent(), then implement mmap() to allow programs
> to map that memory into their user space.
>
> My driver writes 0xDEADBEEF into the first 32-bit word of the memory
> block. When I dump this word from my mmap.c program, it reads 0. It
> seems a zero-page got mapped rather than the buffer.
>
> This is the code, Ieft out all error checking but inserted comments to
> show what I have verified.
>
> int main(void)
> {
> int fd = open("/device_node", O_RDWR | O_SYNC);
> uint32_t *addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> uint32_t data = *addr;
> printf("address 0x%p reads data 0x%08x\n", addr32, (unsigned int)data);
> munmap(addr, 4096);
> close(fd);
> }
>
>
> void ringbuffer_vma_open(struct vm_area_struct *vma)
> {
> }
>
> void ringbuffer_vma_close(struct vm_area_struct *vma)
> {
> }
>
> int ringbuffer_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> {
> /* the buffer allocated with pci_alloc_consistent() */
> void *vaddr = ringbuffer_virt;
> int ret;
>
> /* find the struct page that describes vaddr, the buffer
> * allocated with pci_alloc_consistent() */
> struct page *page = virt_to_page(lro_char->engine->ringbuffer_virt);
> vmf->page = page;
>
> /*** I have verified that vaddr, page, and the pfn correspond
> with vaddr = pci_alloc_consistent() ***/
> ret = vm_insert_pfn(vma, address, page_to_pfn(page));
address is the vmf->virtual_address?
And is the page_to_pfn(page) value correct? As in:
int pfn = page_to_pfn(page);
WARN(pfn << PAGE_SIZE != vaddr,"Something fishy.");
Hm, I think I might have misled you now that I look at that WARN.
The pfn to be supplied has to be physical page frame number. Which in
this case should be your bus addr shifted by PAGE_SIZE. Duh! Try that
value.
I think a better example might be the 'hpet_mmap' code as it is simpler
and it also adds the VM_IO flag.
> return ret;
> }
>
> static const struct vm_operations_struct ringbuffer_vm_ops = {
> .fault = ringbuffer_vma_fault,
> };
>
> static int ringbuffer_mmap(struct file *file, struct vm_area_struct *vma)
> {
> <...extract private data...>
>
> vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>
> vma->vm_flags |= VM_RESERVED | VM_MIXEDMAP;
> vma->vm_private_data = file->private_data;
> vma->vm_ops = &ringbuffer_vm_ops;
> ringbuffer_vma_open(vma);
> return 0;
> }
>
> What did I miss?
I gave you the wrong data :-(
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