[Intel-gfx] [PATCH] drm/i915: Resurrect warning from intel_encoder_crtc_ok()

[Egbert Eich]

Daniel Vetter writes:
 > On Wed, Apr 16, 2014 at 11:46 AM, Egbert Eich <eich at suse.de> wrote:
 > > Bail out if crtc is NULL to keep the driver from crashing.
 > >
 > > Signed-off-by: Egbert Eich <eich at suse.de>
 > > ---
 > >  drivers/gpu/drm/i915/intel_display.c | 5 +++++
 > >  1 file changed, 5 insertions(+)
 > >
 > > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
 > > index c276733..dfebced 100644
 > > --- a/drivers/gpu/drm/i915/intel_display.c
 > > +++ b/drivers/gpu/drm/i915/intel_display.c
 > > @@ -10257,6 +10257,11 @@ intel_modeset_stage_output_state(struct drm_device *dev,
 > >                                 new_crtc = set->crtc;
 > >                 }
 > >
 > > +               if (!new_crtc) {
 > > +                       WARN(1, "crtc not set!");
 > > +                       return -EINVAL;
 > > +               }
 > 
 > This looks really ugly. Can you please supply some context about
 > where/how this blows up? We really shouldn't ever attempt a modeset
 > with a NULL crtc ...

Without 
  [PATCH] drm/i915: Break encoder->crtc link separately in intel_sanitize_crtc()
it is easy to make this happen.
It occurs when there is more than one SDVO connector flagged and the plane - crtc
mapping code for GEN < 4 in intel_sanitize_crtc() triggers.
The reason why this happens is that a still linked encoder has a CRTC nulled
(by break_all_links()). 
The NULL is picked up by:
 new_crtc = connector->new_encoder->base.crtc;

Let me attach a log file I've just generated where the warning code in this 
patch is hit. I had to fake the test for the bogus crtc-plane mapping as I cannot
find a test system with this problem - I do have a log file from an older version
of the driver running on a system at a customer which has an issue with plane-crtc
mapping.

With my other patch this particular situation will not occur any more -
but maybe another ...?

Cheers,
	Egbert.


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