Test your agp(4) before blaming on DRM/DRI!

I was trying to make my Intel i815 and VIA K8T800 chipsets working 
with agp(4) and I found that there were number of issues in the 
driver.  These issues were mainly from adding PCI IDs blindly without 
verifying proper documentation.  On top of that, some drivers do not 
care whether the bridge is supported or not and just attach as 
'generic' bridge, e. g., agp_sis.c and agp_via.c.  This gives users 
false hope and I believe this is wrong.

I found the following from DRI website:

http://dri.sourceforge.net/res/testgart.c

and SuSE Linux had little newer package:

http://www.suse.de/us/private/products/suse_linux/prof/packages_professional/testgart.html

I modified SuSE's to work with FreeBSD.  Test your GART before blaming 
on DRM/DRI!  If aperture size is reported differently from BIOS 
setting, that is not supported correctly, e. g., i815 - different 
aperture size encoding and registers.  If writeback test fails, 
that's more serious problem, e. g., K8T800 - doesn't work at all for 
me.

BTW, you have to unload your drm driver (or recompile kernel if you 
compiled it in) before you test agp.

I hope this helps many confused users.

Cheers,

Jung-uk Kim


* PS: Is there anybody working on AMD64 on-CPU GART driver like this?

http://fxr.watson.org/fxr/source/drivers/char/agp/amd64-agp.c?v=linux-2.6.1

Documentation is here (Section 3.6.11-14):

http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/26094.PDF