[Intel-gfx] [PATCH] drm/i915: reset drm state backpointer in crtc_state

[Daniel Vetter]

On Tue, Apr 07, 2015 at 06:48:15PM +0000, Konduru, Chandra wrote:
> 
> > -----Original Message-----
> > From: Jani Nikula [mailto:jani.nikula at linux.intel.com]
> > Sent: Tuesday, April 07, 2015 2:02 AM
> > To: Konduru, Chandra; intel-gfx at 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 at 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.

You shouldn't ever be chasing the state backpointer of a committed state.
It's ok to clean it up, but chasing that pointer itself is a bug. Why does
the scaler code look at that pointer?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch