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Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression)

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  Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression) Nick Bowler <nbowler@draconx.ca> - 2015-10-06 17:50 +0200
    Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression) Ville Syrjälä <ville.syrjala@linux.intel.com> - 2015-10-07 14:00 +0200
      Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression) Nick Bowler <nbowler@draconx.ca> - 2015-10-07 16:30 +0200
        Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression) Ville Syrjälä <ville.syrjala@linux.intel.com> - 2015-10-07 17:40 +0200
          Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression) Nick Bowler <nbowler@draconx.ca> - 2015-10-07 17:50 +0200
          Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression) Nick Bowler <nbowler@draconx.ca> - 2015-10-07 17:50 +0200
          Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression) Nick Bowler <nbowler@draconx.ca> - 2015-10-07 21:00 +0200
            Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression) Ville Syrjälä <ville.syrjala@linux.intel.com> - 2015-10-07 21:10 +0200

#1240610 — Re: PROBLEM: Intel VGA output busticated on 4.3-rc2 (regression)

Hi,

This issue is still present in 4.3-rc4.

On 9/24/15, Nick Bowler <nbowler@draconx.ca> wrote:
> Testing out 4.3-rc2, first thing I notice is that the VGA output is
> not working.  Specifically, the display is continuously powering on
> and off -- at no point is any image visible on the screen (I am expecting
> to see the console output).  The display connected to the HDMI output is
> working fine.
>
> Linux 4.2 did not suffer from this problem.
>
> In dmesg I see the following messages, which I do not see on a working
> kernel.  Full dmesg from 4.3-rc2 is attached (gzipped).
>
>   [    0.115339] [drm:drm_calc_timestamping_constants] *ERROR* crtc
> 21: Can't calculate constants, dotclock = 0!
>   [    0.117582] [drm:intel_opregion_init] *ERROR* No ACPI video bus found
>
> This is an older machine with Intel G45 graphics.

I was able to identify the commit which fixed my boot crashes, so I
cherry-picked 80aa93128653 ("drm/i915: disable_shared_pll doesn't
work on pre-gen5") on top of all otherwise untestable commits.  This
allowed bisection to proceed:

  b8afb9113c519a8bd742f7df8c424b0af69a75cd is the first bad commit
  commit b8afb9113c519a8bd742f7df8c424b0af69a75cd
  Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
  Date:   Mon Jun 29 15:25:48 2015 +0300

      drm/i915: Keep GMCH DPLL VGA mode always disabled

      We disable the DPLL VGA mode when enabling the DPLL, but we enaable it
      again when disabling the DPLL. Having VGA mode enabled even in unused
      DPLLs can cause problems for CHV, so it seems wiser to always keep it
      disabled. And let's just do that on all GMCH platforms to keep things
      as similar as possible between them.

      Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
      Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
      Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

  :040000 040000 7797d596e73ecf75723375028decd25fbe332ee0
9f90a92eec483919853d68563bbb09a71a305532 M	drivers

Unfortunately it does not revert cleanly on master.

Regards,
  Nick
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#1241409

On Tue, Oct 06, 2015 at 11:42:33AM -0400, Nick Bowler wrote:
> Hi,
> 
> This issue is still present in 4.3-rc4.
> 
> On 9/24/15, Nick Bowler <nbowler@draconx.ca> wrote:
> > Testing out 4.3-rc2, first thing I notice is that the VGA output is
> > not working.  Specifically, the display is continuously powering on
> > and off -- at no point is any image visible on the screen (I am expecting
> > to see the console output).  The display connected to the HDMI output is
> > working fine.
> >
> > Linux 4.2 did not suffer from this problem.
> >
> > In dmesg I see the following messages, which I do not see on a working
> > kernel.  Full dmesg from 4.3-rc2 is attached (gzipped).
> >
> >   [    0.115339] [drm:drm_calc_timestamping_constants] *ERROR* crtc
> > 21: Can't calculate constants, dotclock = 0!
> >   [    0.117582] [drm:intel_opregion_init] *ERROR* No ACPI video bus found
> >
> > This is an older machine with Intel G45 graphics.
> 
> I was able to identify the commit which fixed my boot crashes, so I
> cherry-picked 80aa93128653 ("drm/i915: disable_shared_pll doesn't
> work on pre-gen5") on top of all otherwise untestable commits.  This
> allowed bisection to proceed:
> 
>   b8afb9113c519a8bd742f7df8c424b0af69a75cd is the first bad commit
>   commit b8afb9113c519a8bd742f7df8c424b0af69a75cd
>   Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
>   Date:   Mon Jun 29 15:25:48 2015 +0300
> 
>       drm/i915: Keep GMCH DPLL VGA mode always disabled
> 
>       We disable the DPLL VGA mode when enabling the DPLL, but we enaable it
>       again when disabling the DPLL. Having VGA mode enabled even in unused
>       DPLLs can cause problems for CHV, so it seems wiser to always keep it
>       disabled. And let's just do that on all GMCH platforms to keep things
>       as similar as possible between them.
> 
>       Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>       Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
>       Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
>   :040000 040000 7797d596e73ecf75723375028decd25fbe332ee0
> 9f90a92eec483919853d68563bbb09a71a305532 M	drivers
> 
> Unfortunately it does not revert cleanly on master.

@@ -1790,13 +1790,13 @@ static void i9xx_disable_pll(struct intel_crtc *crtc)
        /* Make sure the pipe isn't still relying on us */
        assert_pipe_disabled(dev_priv, pipe);
 
-       I915_WRITE(DPLL(pipe), 0);
+       I915_WRITE(DPLL(pipe), DPLL_VGA_MODE_DIS);
        POSTING_READ(DPLL(pipe));
 }


That hunk is the only relevant part for your machine. Can you try to revert
just that manually?

But I'm really surprised that would have any effect since we only used
to enable "VGA mode" when the DPLL is off. And when the DPLL is off,
there's nothing on the screen anyway.

-- 
Ville Syrjälä
Intel OTC
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#1241550

On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Tue, Oct 06, 2015 at 11:42:33AM -0400, Nick Bowler wrote:
>> On 9/24/15, Nick Bowler <nbowler@draconx.ca> wrote:
>> > Testing out 4.3-rc2, first thing I notice is that the VGA output is
>> > not working.  Specifically, the display is continuously powering on
>> > and off -- at no point is any image visible on the screen (I am
>> > expecting to see the console output).  The display connected to the
>> > HDMI output is working fine.
[...]
>>   b8afb9113c519a8bd742f7df8c424b0af69a75cd is the first bad commit
>>   commit b8afb9113c519a8bd742f7df8c424b0af69a75cd
>>   Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>   Date:   Mon Jun 29 15:25:48 2015 +0300
>>
>>       drm/i915: Keep GMCH DPLL VGA mode always disabled
[...]
> @@ -1790,13 +1790,13 @@ static void i9xx_disable_pll(struct intel_crtc
> *crtc)
>         /* Make sure the pipe isn't still relying on us */
>         assert_pipe_disabled(dev_priv, pipe);
>
> -       I915_WRITE(DPLL(pipe), 0);
> +       I915_WRITE(DPLL(pipe), DPLL_VGA_MODE_DIS);
>         POSTING_READ(DPLL(pipe));
>  }
>
>
> That hunk is the only relevant part for your machine. Can you try to revert
> just that manually?
>
> But I'm really surprised that would have any effect since we only used
> to enable "VGA mode" when the DPLL is off. And when the DPLL is off,
> there's nothing on the screen anyway.

Nevertheless, manually reverting just that hunk seems to fix it.

Thanks,
  Nick
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#1241604

[Multipart message — attachments visible in raw view] — view raw

On Wed, Oct 07, 2015 at 10:29:22AM -0400, Nick Bowler wrote:
> On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > On Tue, Oct 06, 2015 at 11:42:33AM -0400, Nick Bowler wrote:
> >> On 9/24/15, Nick Bowler <nbowler@draconx.ca> wrote:
> >> > Testing out 4.3-rc2, first thing I notice is that the VGA output is
> >> > not working.  Specifically, the display is continuously powering on
> >> > and off -- at no point is any image visible on the screen (I am
> >> > expecting to see the console output).  The display connected to the
> >> > HDMI output is working fine.
> [...]
> >>   b8afb9113c519a8bd742f7df8c424b0af69a75cd is the first bad commit
> >>   commit b8afb9113c519a8bd742f7df8c424b0af69a75cd
> >>   Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >>   Date:   Mon Jun 29 15:25:48 2015 +0300
> >>
> >>       drm/i915: Keep GMCH DPLL VGA mode always disabled
> [...]
> > @@ -1790,13 +1790,13 @@ static void i9xx_disable_pll(struct intel_crtc
> > *crtc)
> >         /* Make sure the pipe isn't still relying on us */
> >         assert_pipe_disabled(dev_priv, pipe);
> >
> > -       I915_WRITE(DPLL(pipe), 0);
> > +       I915_WRITE(DPLL(pipe), DPLL_VGA_MODE_DIS);
> >         POSTING_READ(DPLL(pipe));
> >  }
> >
> >
> > That hunk is the only relevant part for your machine. Can you try to revert
> > just that manually?
> >
> > But I'm really surprised that would have any effect since we only used
> > to enable "VGA mode" when the DPLL is off. And when the DPLL is off,
> > there's nothing on the screen anyway.
> 
> Nevertheless, manually reverting just that hunk seems to fix it.

Hmm. You said VGA has the problem, but HDMI does not. Was the problem
happening even when you have both displays enabled at the same time, or
just when VGA was enabled alone?

I've attached two potential patches that might help. Can you give a try
to just patch 1, and if that alone doesn't help then both patches
together?

-- 
Ville Syrjälä
Intel OTC

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#1241610

On 10/7/15, Nick Bowler <nbowler@draconx.ca> wrote:
> On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
>> On Wed, Oct 07, 2015 at 10:29:22AM -0400, Nick Bowler wrote:
>>> On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
>>> > On Tue, Oct 06, 2015 at 11:42:33AM -0400, Nick Bowler wrote:
>>> >> On 9/24/15, Nick Bowler <nbowler@draconx.ca> wrote:
>>> >> > Testing out 4.3-rc2, first thing I notice is that the VGA output is
>>> >> > not working.  Specifically, the display is continuously powering on
>>> >> > and off -- at no point is any image visible on the screen (I am
>>> >> > expecting to see the console output).  The display connected to the
>>> >> > HDMI output is working fine.
>>> [...]
>> Hmm. You said VGA has the problem, but HDMI does not. Was the problem
>> happening even when you have both displays enabled at the same time, or
>> just when VGA was enabled alone?
>
> When I boot with HDMI cable disconnected, there is no change in behaviour
> for the VGA output.

Clarification: normally both displays are connected.  So the original issue is
that only one of two displays are working.
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#1241612

On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Wed, Oct 07, 2015 at 10:29:22AM -0400, Nick Bowler wrote:
>> On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
>> > On Tue, Oct 06, 2015 at 11:42:33AM -0400, Nick Bowler wrote:
>> >> On 9/24/15, Nick Bowler <nbowler@draconx.ca> wrote:
>> >> > Testing out 4.3-rc2, first thing I notice is that the VGA output is
>> >> > not working.  Specifically, the display is continuously powering on
>> >> > and off -- at no point is any image visible on the screen (I am
>> >> > expecting to see the console output).  The display connected to the
>> >> > HDMI output is working fine.
>> [...]
> Hmm. You said VGA has the problem, but HDMI does not. Was the problem
> happening even when you have both displays enabled at the same time, or
> just when VGA was enabled alone?

When I boot with HDMI cable disconnected, there is no change in behaviour
for the VGA output.

> I've attached two potential patches that might help. Can you give a try
> to just patch 1, and if that alone doesn't help then both patches
> together?

I will try.

Cheers,
  Nick
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#1241732

On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Wed, Oct 07, 2015 at 10:29:22AM -0400, Nick Bowler wrote:
>> On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
>> > On Tue, Oct 06, 2015 at 11:42:33AM -0400, Nick Bowler wrote:
>> >> On 9/24/15, Nick Bowler <nbowler@draconx.ca> wrote:
>> >> > Testing out 4.3-rc2, first thing I notice is that the VGA output is
>> >> > not working.  Specifically, the display is continuously powering on
>> >> > and off -- at no point is any image visible on the screen (I am
>> >> > expecting to see the console output).  The display connected to the
>> >> > HDMI output is working fine.
>> [...]
> I've attached two potential patches that might help. Can you give a try
> to just patch 1, and if that alone doesn't help then both patches
> together?

Patch #1: no change.
Patch #1+#2: this works.

Regards,
  Nick
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#1241739

On Wed, Oct 07, 2015 at 02:50:34PM -0400, Nick Bowler wrote:
> On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > On Wed, Oct 07, 2015 at 10:29:22AM -0400, Nick Bowler wrote:
> >> On 10/7/15, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> >> > On Tue, Oct 06, 2015 at 11:42:33AM -0400, Nick Bowler wrote:
> >> >> On 9/24/15, Nick Bowler <nbowler@draconx.ca> wrote:
> >> >> > Testing out 4.3-rc2, first thing I notice is that the VGA output is
> >> >> > not working.  Specifically, the display is continuously powering on
> >> >> > and off -- at no point is any image visible on the screen (I am
> >> >> > expecting to see the console output).  The display connected to the
> >> >> > HDMI output is working fine.
> >> [...]
> > I've attached two potential patches that might help. Can you give a try
> > to just patch 1, and if that alone doesn't help then both patches
> > together?
> 
> Patch #1: no change.
> Patch #1+#2: this works.

Cool. I can see similar effects when manually frobbing the register on
my 946GZ, except somehow it still manages to work without these
patches. Not quite sure why that is.

But anyway, I'll polish the patches a bit and send them out.

-- 
Ville Syrjälä
Intel OTC
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