Re: That horrible hack from hell called A20

Kai Germaschewski
2000-12-06T10:47:41Z

On Tue, 5 Dec 2000, Linus Torvalds wrote:

> On Wed, 6 Dec 2000, Kai Germaschewski wrote:
>
> >
> > On Tue, 5 Dec 2000, H. Peter Anvin wrote:
> >
> > > If you have had A20M# problems with any kernel -- recent or not --
> > > *please* try this patch, against 2.4.0-test12-pre5:
> >
> > Just a datapoint: This patch doesn't fix the problem here (Sony
> > PCG-Z600NE). Still the spontaneous reboot exactly the moment I expect to
> > get my console back from resumeing.

First of all, I tested removing the "or $2" in hpa's patch.
That made resume work. Then, putting back the "or" but removing the
"and $0xfe" had no effect at all (i.e. resume -> reboot).

I suppose not setting bit 1 made fast A20 enable not succeed, so kbc A20
was used -> resume works fine.

With setting bit 1 and with or w/o clearing bit 0, fast A20 enable seems
to succeed -> kbc A20 is not used -> resume reboots.

> Want to bet $5 USD that suspend/resume saves the keyboard A20 state, but
> does NOT save the fast-A20 gate information?

I suppose I'ld loose that bet.

> So anything that enables A20 with only the fast A20 gate will find that
> A20 is disabled again on resume.
>
> Which would make Linux _really_ unhappy, needless to say. Instant death in
> the form of a triple fault (all of the Linux kernel code is in the 1-2MB
> area, which would be invisible), resulting in an instant reboot.

Makes sense to me.

test12-pre6 now works perfectly :-)

--Kai