Memory mapped IO in video drivers

Hello,

I have an xFree86 video driver for a custom gfx board, and am running into a
problem with the memory mapped IO.  The display portion of the driver works
just fine, however we are also trying to support I2C/DDC.  

The quick explanation of the problem is that the IO address range to the
video registers we need for I2C is getting mapped in and out multiple times
during the X session.  Sometimes the registers are there, other times they
aren't (i.e., we read 0xFF for all registers instead of valid data).

The problem occurs with all of the mapped registers, not just the I2C ones,
but the IO space always seems to be mapped in properly during accelerated
drawing functions, it's just when we try to access I2C through our back door
that it is rather unpredictable.

The pointer to the address range itself is not changing, just the validity
of the data.  Also, it doesn't appear that the BAR for the IO registers is
being moved.

The registers are being mapped in during ScreenInit with a call to
xf86MapPciMem() with the VIDMEM_MMIO_32BIT flag.  Our code to unmap the
registers with xf86UnMapVidMem() doesn't get called until the X session is
closed.

So, is there some part of the XFree86 server that would be mapping and
unmapping the address space behind my back?  How can I indicate to the X
server that this memory is non-relocatable and has to be permenant for the
duration of the X session?

Also, I have noticed that the memory mapped IO gets unmapped whenever I
temporarily switch out of the X server to a virtual terminal in VGA mode,
and then the IO gets mapped in again when I switch back to the X server.  I
know our driver code for EnterVT() and LeaveVT() isn't doing this, so where
does this happen in the server code?  Perhaps it could be a related issue?

This is a multiple board configuration (four monitors, two per board), so
perhaps its not something that has really been tested heavily before?

BTW, if it matters, the video driver is being loaded as a module, not
compiled into the kernel.

Any help or tips here would be appreciated.  I have already been perusing
the only XF86 video driver resource I could find at
http://xfree86.activeventure.org/design/DESIGN.html
<http://xfree86.activeventure.org/design/DESIGN.html> .

Thanks,
Matt

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