Mapping PCI memory to user-space

[joncglenn]

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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[Jiri Slaby]

On 10/24/2007 08:59 AM, joncglenn wrote:
> 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)

I think you can use the method used for exporting pci resources in /sys. See
pci_mmap_resource. Don't know if this was yet in 2.6.9...

regards,
--
Jiri Slaby (jiri...@gmail.com)
Faculty of Informatics, Masaryk University

[Roland Dreier]

> 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)

There is no relationship between the address returned from ioremap and
what you pass into io_remap_page_range(). ioremap gives you a kernel
virtual address for the PCI address you remap. io_remap_page_range()
creates a userspace mapping in the same way, and you should pass in
the PCI address exactly the same way you pass in the PCI address into
ioremap. io_remap_pfn_range() takes a PFN ("page frame number"),
which is basically the PCI address you want to map divided by
PAGE_SIZE. The main reason for using PFNs is that they allow you to
map addresses above 4G even if sizeof long is only 4.

In your code:

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

This gives you a kernel mapping that you can use with readl(),
writel() etc to access the PCI memory from the kernel.

To map to userspace, this:

> if (io_remap_page_range(vma, phyaddr, vma->vm_start, vsize, vma->vm_page_prot))

should use phyaddr as you have it here:

> // phyaddr = physical address of PCI memory area

This is just wrong:

> unsigned long phy = __pa(dev->region_start + off);

__pa() doesn't work on addresses returned from ioremap. Just use the
same resource address you passed into ioremap.

- R.