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SubjectRe: Possible critical VIA vt82c686a chip bug (private question)
On Thu, Oct 26, 2000 at 04:42:31PM +0200, Yoann Vandoorselaere wrote:

> > On Thu, Oct 26, 2000 at 04:20:43PM +0200, Yoann Vandoorselaere wrote:
> >
> > > ...
> > >
> > > Have you any idea what is the relation between time and this chip ?
> > >
> > > Also, I'm experiencing the problem for several month on my
> > > workstation and I never could find where it was comming from...
> > > how did you do ?
> >
> > Well, it integrates both the i8253 PIT and the vt82c586 IDE controller.
> >
> > I first located the wrong time was coming from gettimeofday() and not
> > from the other sources of time the kernel provides. And then I was
> > tracking the problem (which actually is an underflow - the chip bug
> > causes some time offset variables go negative - 0xffffffff microseconds
> > is about 1:20 hours). And this way I got to the spot where the patch
> > cures the problem.
>
> Ok, here is what I experienced :
>
> First what is strange is that :
> - I'm using SCSI
> - I just have an IDE disk for mp3.
> The IDE subsystem is never used heavilly...
>
> I've experienced the problem after some time of
> heavy scsi IO, my screen under X was going black (like with dpms)
> When I was moving the mouse, the image was coming back
> for < 1 seconds, then black screen...
>
> The only fix was to kill X then to reboot.
>
> Anyway, thanks for your explaination...
> I'll do a feedback for this patch ASAP.

Interesting. If it's caused by SCSI as well (might be), then it's not
caused by heavy IDE activity but rather than that it could be heavy
BusMastering activity instead (The IDE chip does BM as well).

I'm still wondering if it could be a Linux kernel bug (bad/concurrent
accesses to the i8253 registers), this has to be checked.

--
Vojtech Pavlik
SuSE Labs
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