question about user space addressed, mmap, and getting phys address

[John-Mark Gurney]

Sean McNeil wrote this message on Sat, Nov 01, 2003 at 14:40 -0800:
> Sorry I am not on the list, but I was hoping someone here might be able
> to help me.  I have a design that I cannot change that does the
> following:
> 
> 1) Calls mmap on a chunk of memory that the device driver uses to DMA to
> a video decoder.
> 
> 2) This chunk of memory is treated as several DMA buffers.  There is an
> ioctl setup to indicate when a section of that memory is being used and
> when it is freed (usage count).
> 
> I need to take the address from the mmap, add an offset, send it through
> an ioctl, and then relate it back to the physical address that it was
> originally mapped from.
> 
> Unfortunately, the address I get from the ioctl is a user-space address
> and when I use vtophys I get back 0.  Is there some other mechanism to
> convert a user-space address to a physical address?
> 
> Any and all help will be greatly appreciated.

I wrote a fucntion for a video encoder card that does this.  I think
passing in physical address is a bad thing, (and svgalib is nice and
mmap's the video frame buffer for you) so I made my driver require
you to pass the address via ioctl pointing to it's local buffer.

The function is a bit long, but look at
http://people.FreeBSD.org/~jmg/zoran-0.5.tar.gz
in the file zoran-0.5/dev/zr/zr_os.c the function verify_contig.

I've stolen that code from other parts of the kernel that do something
similar, but I forget where now.

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."