Currently, the call to linuxPciOpenFile() is always made for read
only access which causes the subseqent mmap call to fail when the
memory is mapped read/write.  The following patch fixes the problem:

Index: xc/programs/Xserver/hw/xfree86/os-support/bus/linuxPci.c
===================================================================
--- xc/programs/Xserver/hw/xfree86/os-support/bus/linuxPci.c.orig      
2006-09-18 16:38:08.067521978 -0700
+++ xc/programs/Xserver/hw/xfree86/os-support/bus/linuxPci.c    2006-08-10
19:32:19.503681311 -0700
@@ -569,7 +569,8 @@
 
        xf86InitVidMem();
 
-       if (((fd = linuxPciOpenFile(Tag ,FALSE)) < 0) ||
+       prot = (Flags & VIDMEM_READONLY) == 0;
+       if (((fd = linuxPciOpenFile(Tag, prot)) < 0) ||
            (ioctl(fd, mmap_ioctl, 0) < 0))
            break;