AMD64-AGP pb with AGP APERTURE on IWILL DK8N

[Vincent ETIENNE <ve@vetienne.net>]

Hello ALL,

I have some problem with AGP initialization with my board : IWLL DK8N (Bi 
opteron chipset NFORCE3 ). I use kernel 2.6.10-rc3-mm1, but i have try with 
different kernel always with the same result :

IOMMU reports a 128MB aperture for CPU0 ( that's the value i used in my bios) 
at F0000000 but only 32MB at 4000000 for CPU1 and declare i have no valid 
aperture as show in this dmesg extract. 

Checking aperture...
CPU 0: aperture @ f0000000 size 128 MB
CPU 1: aperture @ 4000000 size 32 MB
Aperture from northbridge cpu 1 too small (32 MB)
AGP bridge at 00:00:00
Aperture from AGP @ f0000000 size 4096 MB (APSIZE 0)
Aperture from AGP bridge too small (0 MB)
Your BIOS doesn't leave a aperture memory hole

So i have forced the value at CPU1 to be the same as CPU0 in 
arch/x86_64/kernel/aperture.c function iommu_hole_init with the following 
code. Don't asked me what i have done i have quite no idea of what is 
involved by this modification. 

I have add 2 var for memorizing value of aperture_size and base of the first 
cpu and set the value of the second one to the value of the first one on case 
they are diferent ( added line marked with a "+" sign ).

void __init iommu_hole_init(void)
{
 int fix, num;
 u32 aper_size, aper_alloc = 0, aper_order;
 u64 aper_base;
+ u32 last_aper_order = 0;
+ u64 last_aper_base = 0;
 int valid_agp = 0;

 if (iommu_aperture_disabled || !fix_aperture)
  return;
 printk("Checking aperture...\n");
 fix = 0;
 for (num = 24; num < 32; num++) {
  char name[30];
  if (read_pci_config(0, num, 3, 0x00) != NB_ID_3)
   continue;

  iommu_aperture = 1;
  aper_order = (read_pci_config(0, num, 3, 0x90) >> 1) & 7;
  aper_size = (32 * 1024 * 1024) << aper_order;
  aper_base = read_pci_config(0, num, 3, 0x94) & 0x7fff;
  aper_base <<= 25;
  printk("CPU %d: aperture @ %Lx size %u MB\n", num-24,
  aper_base, aper_size>>20);
+  if ( last_aper_order )
+ {
+   if ( aper_order != last_aper_order )
+   {
+    printk("Aperture size changed!! use old one (%x,%x)", last_aper_order, 
last_aper_base );
+    write_pci_config(0, num, 3, 0x90, last_aper_order<<1);
+    write_pci_config(0, num, 3, 0x94, last_aper_base>>25);
+    aper_order = last_aper_order;
+    aper_base = last_aper_base;
+    aper_size = (32 * 1024 * 1024) << aper_order;
+   }
+ }
+  last_aper_order = aper_order;
+  last_aper_base = aper_base;

Rest of the code unchanged.

Now agp is enabled 8x, SBA and fast write activated  (as seeen 
in /proc/driver/nvidia/agp/status ) and i'm very pleased but also frustated 
as i have no idea of that i have done.

Do you think it's more a bios problem (something not initialized correctly by 
the bios as it seem ) or could it be a kernel bug ?  Someone could explain 
what value sould be returned ? Is my modification secured (at least for my 
board ) i.e. is this modification could harm some hardware ?

I wish to be personally CC'ed the answers/comment as i'm not a subscriber of a 
list. 

Thanks for your time.

Vincent ETIENNE