userspace testing an ati fb driver

Benjamin Herrenschmidt benh at
Thu Dec 4 11:06:46 EST 2003

On Wed, 2003-12-03 at 20:44, random wrote:
> On my Powerbook, /proc/iomem lists 0xb0000000-0xb000ffff as the location
> of the programming registers for my ATI Radeon R250 Lf.
> This seems to be the same spot XFree86 finds in its log:
> (II) RADEON(0): MMIO registers at 0xb0000000
> I've been trying to mimic the XFree86 fb accel code to make a Linux 2.6 fb
> port, but i've had little luck. To try to pare down the new code, I've
> written a userspace program which will open "/dev/mem" and then mmap in
> this file starting at '0xb0000000' going for 0x10000 bytes.  Poking at the
> "registers" there seems to have no effect; reading from these "registers"
> (for example, to verify the engine idling) indicates that I'm perhaps
> reading from the wrong place in memory, i.e. the engine never indicates
> that it's idle.  Any ideas?

That should work, make sure you are using proper memory barriers for
your IO accesses though (eieio instructions)

Enclosed is an example of a little program I use to dump the radeon


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