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Old 03-21-2011, 06:38 AM
Chris Wilson
 
Default Bug#619019: i915: Remove pipe A force quirk for 855GM and 845G

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.)

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.

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.)
-Chris

--
Chris Wilson, Intel Open Source Technology Centre



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Old 03-22-2011, 02:05 AM
Ben Hutchings
 
Default Bug#619019: i915: Remove pipe A force quirk for 855GM and 845G

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.
 
Old 03-22-2011, 06:17 AM
Chris Wilson
 
Default Bug#619019: i915: Remove pipe A force quirk for 855GM and 845G

On Tue, 22 Mar 2011 03:05:45 +0000, Ben Hutchings <ben@decadent.org.uk> wrote:
> 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?

It is mentioned as a "feature" in several places of the specs for the 830G
chipset.

> 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.

That sounds promising that the code was indeed papering over bugs...
Doesn't sound too promising for the state of our code though.

> > 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.

I'd still prefer a patch for each quirk removal.
Along with a tested-by. ;-)

The little bit of time invested now in preparing small commits with be of
great benefit should anyone need to investigate later. We have to
gradually wean ourselves off the quirk table and convince everybody that
the code does actually know how to modeset the chip!

> 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.

During the switch-over from BIOS we disable all the outputs - instant bug.

Many thanks for preparing these patches,
-Chris

--
Chris Wilson, Intel Open Source Technology Centre



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Old 03-22-2011, 10:04 AM
Chris Wilson
 
Default Bug#619019: i915: Remove pipe A force quirk for 855GM and 845G

On Tue, 22 Mar 2011 03:05:45 +0000, Ben Hutchings <ben@decadent.org.uk> wrote:
> On Mon, 2011-03-21 at 07:38 +0000, Chris Wilson wrote:
> > 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.

Yes. Having just been poked by Julien to look at the original quirk
table and so seeing the generic match all 855GM, please do send that
patch.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre



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Old 03-22-2011, 02:47 PM
Jesse Barnes
 
Default Bug#619019: i915: Remove pipe A force quirk for 855GM and 845G

On Tue, 22 Mar 2011 03:05:45 +0000
Ben Hutchings <ben@decadent.org.uk> wrote:

> 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?

The DDX driver had an option to force enable pipe A, and we told people
to report bugs when they needed it. So we got a bunch from Ubuntu and
elsewhere and added them without too much investigation into the root
cause (as you say below it could have been something else).

> > 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.

Yes, definitely possible. We didn't have all the assertion checks we
have now, so we may have just been masking other problems without
knowing it.

--
Jesse Barnes, Intel Open Source Technology Center



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