Re: [PATCH] drm/i915: reset drm state backpointer in crtc_state

["Konduru, Chandra" <chandra.konduru@intel.com>]

> -----Original Message-----
> From: Jani Nikula [mailto:jani.nikula@linux.intel.com]
> Sent: Tuesday, April 07, 2015 2:02 AM
> To: Konduru, Chandra; intel-gfx@lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH] drm/i915: reset drm state backpointer in
> crtc_state
> 
> On Mon, 06 Apr 2015, Chandra Konduru <chandra.konduru@intel.com> wrote:
> > At end of intel_crtc_set_config, reset crtc_state's drm_state back
> > pointer to null.
> 
> This does not tell me anything that reading the patch already didn't. Please
> explain *why* this is needed in the commit message. What breaks without it? If
> this fixes a regression, please indicate which commit regressed.

Once atomic transaction is done, live crtc_state (i.e., intel_crtc->config) is 
carrying back pointer to drm_atomic_state which is freed. When a new 
non-atomic transaction is made (crtc_disable triggered off from set_mode), 
this stale pointer is carried into that transaction. 
Depending on timing, this causes issue to scaler feature that I am working 
if panel fit to be disabled during crtc_disable.

It has potential to cause issues to wm work that Matt is doing, but not sure.

> 
> BR,
> Jani.
> 
> >
> > Signed-off-by: Chandra Konduru <chandra.konduru@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c |    4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > b/drivers/gpu/drm/i915/intel_display.c
> > index c84926b..f9c2e4d 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -12451,8 +12451,10 @@ fail:
> >  	}
> >
> >  out_config:
> > -	if (state)
> > +	if (state) {
> >  		drm_atomic_state_free(state);
> > +		to_intel_crtc(set->crtc)->config->base.state = NULL;
> > +	}
> >
> >  	intel_set_config_free(config);
> >  	return ret;
> > --
> > 1.7.9.5
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> --
> Jani Nikula, Intel Open Source Technology Center
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