[Intel-gfx] [PATCH 4/4] drm/atomic-helpers: Make encoder picking more robust

[Daniel Vetter]

On Tue, Aug 04, 2015 at 11:56:08AM +0300, Ander Conselvan De Oliveira wrote:
> For the series:
> 
> Reviewed-by: Ander Conselvan de Oliveira <conselvan2 at gmail.com>

Thanks for the review.
-Daniel
> 
> 
> On Mon, 2015-08-03 at 17:24 +0200, Daniel Vetter wrote:
> > We've had a few issues with atomic where subtle bugs in the encoder
> > picking logic lead to accidental self-stealing of the encoder,
> > resulting in a NULL connector_state->crtc in update_connector_routing
> > and subsequent.
> > 
> > Linus applied some duct-tape for an mst regression in
> > 
> > commit 27667f4744fc5a0f3e50910e78740bac5670d18b
> > Author: Linus Torvalds <torvalds at linux-foundation.org>
> > Date:   Wed Jul 29 22:18:16 2015 -0700
> > 
> >     i915: temporary fix for DP MST docking station NULL pointer dereference
> > 
> > But that was incomplete (the code will still oops when debuggin is
> > enabled) and mangled the state even further. So instead WARN and bail
> > out as the more future-proof option.
> > 
> > Cc: Theodore Ts'o <tytso at mit.edu>
> > Cc: Linus Torvalds <torvalds at linux-foundation.org>
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > ---
> >  drivers/gpu/drm/drm_atomic_helper.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 8694ca9beee3..9dcc7280e572 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -234,13 +234,14 @@ update_connector_routing(struct drm_atomic_state *state, int conn_idx)
> >  		}
> >  	}
> >  
> > +	if (WARN_ON(!connector_state->crtc))
> > +		return -EINVAL;
> > +
> >  	connector_state->best_encoder = new_encoder;
> > -	if (connector_state->crtc) {
> > -		idx = drm_crtc_index(connector_state->crtc);
> > +	idx = drm_crtc_index(connector_state->crtc);
> >  
> > -		crtc_state = state->crtc_states[idx];
> > -		crtc_state->mode_changed = true;
> > -	}
> > +	crtc_state = state->crtc_states[idx];
> > +	crtc_state->mode_changed = true;
> >  
> >  	DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] using [ENCODER:%d:%s] on [CRTC:%d]\n",
> >  			 connector->base.id,

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch