5.3.8. Memory mapping

• allows userspace direct access to device memory

• benefits:
  • avoids buffering: can improve performace
  • direct access to registers can avoid many ioctl

• only makes sense in certain circumstances: e.g. not for stream oriented devices

API: mmap

file operation

int *mmap (struct file *filp, struct vm_area_struct *vma);

build page tables

int remap_pfn_range(struct vm_area_struct *vma, unsigned long virt_addr,
          unsigned long pfn, unsigned long size, pgprot_t prot);

/* identical to above on most plattforms: */
int io_remap_pfn_range(struct vm_area_struct *vma, unsigned long virt_addr, 
             unsigned long phys_addr, unsigned long size, pgprot_t prot);