linux-kernel - Mapping PCI memory to user-space

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Date:	Tue, 23 Oct 2007 23:59:06 -0700 (PDT)
From:	joncglenn <joncglenn@...mail.com>
To:	linux-kernel@...r.kernel.org
Subject: Mapping PCI memory to user-space


I am writing a driver to map a PCI board memory space (pcibar2) into a
user-space vma via 'mmap'.  What is the relationship between the address
returned from ioremap and the type of address needed in the
'io_remap_page_range' or 'remap_pfn_range' functions?  How about the
following? (I am developing under RHEL4 and a 2.6.9 kernel)

In the 'init' part of the driver:

     dev.pcibar2 = ioremap_nocache(resource,size);
     dev.region_start = dev.pcibar2 + offset;     // RAM is at some offset
from base
     dev.region_size  = <some size>

In the mydriver_mmap function:

static ssize_t mydriver_mmap (struct file *filp,
                                                    struct vm_area_struct
*vma)
{
  // off             = convert vm_pgoff back to user-space mmap 'off' value
  // phyaddr   = physical address of PCI memory area
  // vsize         = total size of area user wants to map
  // psize         = total avail size in device
  struct mydriver_dev *dev = filp->private_data;
  unsigned long off              = vma->vm_pgoff << PAGE_SHIFT;
  unsigned long phy            = __pa(dev->region_start + off);
  unsigned long vsize          = vma->vm_end - vma->vm_start;
  unsigned long psize          = dev->region_size - off;

  if (vsize > psize)
     return -EINVAL; /* spans too high */
  if (io_remap_page_range(vma, phyaddr, vma->vm_start, vsize,
vma->vm_page_prot))
     return -EAGAIN;

  vma->vm_ops    = &mydriver_vm_ops;
  vma->vm_flags |= VM_IO | VM_RESERVED;
  mydriver_vma_open(vma);

  return 0;
}

-- 
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