Re: [PATCH 1/2] i915: Remove pipe A force quirk for 855GM and 845G

Ben Hutchings
2011-03-22T03:05:56Z

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On Mon, 2011-03-21 at 07:38 +0000, Chris Wilson wrote:
> On Sun, 20 Mar 2011 23:07:04 +0000, Ben Hutchings <ben@decadent.org.uk> wrote:
> > Applying this quirk to the 855GM in all systems causes regressions
> > (Debian bugs #493096, #619019). Instead, apply the quirk to specific
> > models as listed in the old X driver.
> >
> > I don't see any explanation for this quirk being applied to the 845G,
> > except perhaps that VT switching used to hang if pipe A was turned
> > off. However, that seems to be a problem only when using UMS. So
> > remove the quirk for the 845G as well.
>
> The quirk should only be required for 830M due to the numerous instances
> where a unit on the second pipe is actually wired into the clock on the
> first pipe. (And so it is easiest to keep the first pipe active at all
> times.)

When you say 'wired into', is this part of the chip design or something
done on the board?

Jesse, why did you add the quirk for other chips?

> I'd prefer the quirk table to disappear and simply be replaced by
> IS_830M(). However, that requires testing and so should only be done
> piecemeal. And leaves some doubt as to why the other machines were in the
> quirk table in the first place.

The commit messages referring to VT switching suggest that the problems
related to disabling part A may actually have been related to handover
to the console driver before KMS.

> Can you please repost each of these removals as a separate patch and lets
> try and get a tested-by for each one? (Make sure the tester includes the
> model name for his machine so we can double check the veracity of the
> change.)

I already have 4 regression reports for the addition of the quirk for
855GM:

http://bugs.debian.org/618665
http://bugs.debian.org/618997
http://bugs.debian.org/619019
http://bugs.debian.org/619192

and one on an unidentified (as yet) chip:

http://bugs.debian.org/619199

So I can just send a patch to revert 855GM.

The odd thing about these reports is that the regression is reported to
occur before the system has ever been suspended, and to be fixed (or
mitigated) by suspending and resuming. I don't understand why the quirk
even comes into play during boot.

Ben.

--
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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