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));
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?
Regards,
--
Leon
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