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

[Nick Bowler]

On 10/7/15, Ville Syrjälä <ville.syrjala at linux.intel.com> wrote:
> On Tue, Oct 06, 2015 at 11:42:33AM -0400, Nick Bowler wrote:
>> On 9/24/15, Nick Bowler <nbowler at 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 at 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