Re: Athlon: Try this (was: Re: Athlon bug stomping #2)

[Jonathan Morton <chromi@cyberspace.org>]

>  > > +static void __init pci_fixup_athlon_bug(struct pci_dev *d)
>>  > +{
>>  > +       u8 v;
>>  > +       pci_read_config_byte(d, 0x55, &v);
>>  > +       if(v & 0x80) {
>>  > +               printk(KERN_NOTICE "Stomping on Athlon bug.\n");
>>  > +               v &= 0x7f; /* clear bit 55.7 */
>>  > +               pci_write_config_byte(d, 0x55, v);
>>  > +       }
>>  > +}
>>  >
>>  > Well, these are cosmetic changes anyway...
>>  > What is more important now:
>>  > 1) Do we have people who still see Athlon bug with the patch?
>>  > 2) Do Alan read these messages? ;-)
>>
>>  Im watching the discussion with interest. If it proves to be the magic
>>  bullet I will ask VIA for guidance on the issue
>
>Not being a developer or guru on the internal software workings of the
>hardware here, I have to ask, does this clear up some bug, or does it
>disable the optimizations causing the problem? Is this a *fix* or a
>band-aid?

AFAICT, it's a *fix*.  The register in question is "for debug use 
only, never write anything other than zero in it" but generally shows 
non-zero when a faulty BIOS is installed.  We're zeroing the bit that 
appears to cause the problem.  It's highly unlikely to be an extra 
optimisation - if it is, it's an unsafe one.

-- 
--------------------------------------------------------------
from:     Jonathan "Chromatix" Morton
mail:     chromi@cyberspace.org  (not for attachments)
website:  http://www.chromatix.uklinux.net/vnc/
geekcode: GCS$/E dpu(!) s:- a20 C+++ UL++ P L+++ E W+ N- o? K? w--- O-- M++$
           V? PS PE- Y+ PGP++ t- 5- X- R !tv b++ DI+++ D G e+ h+ r++ y+(*)
tagline:  The key to knowledge is not to rely on people to teach you it.