[REGRESSION] Re: i915 driver crashes on T540p if docking station attached

[Theodore Ts'o]

On Thu, Jul 30, 2015 at 04:40:02PM +0200, Daniel Vetter wrote:
> On Wed, Jul 29, 2015 at 10:18:16PM -0700, Linus Torvalds wrote:
> >  drivers/gpu/drm/drm_atomic_helper.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 5b59d5ad7d1c..aac212297b49 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -230,10 +230,12 @@ update_connector_routing(struct drm_atomic_state *state, int conn_idx)
> >  	}
> >  
> >  	connector_state->best_encoder = new_encoder;
> > -	idx = drm_crtc_index(connector_state->crtc);
> > +	if (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;
> > +	}
> 
> This shouldn't happen since if it does we ended up stealing the encoder
> from the connector itself (we do check for connector_state->crtc earlier)
> and that would be a bug. I haven't figured out a precise theory but my
> guess is on the best_encoder selection, and indeed dp mst encoder
> selection seems to have gone belly up in 4.2 with the bisected commit.

Well, I just tested Linus's patch and it works.

BTW, is there any chance that I can suspend my laptop, and then move
it from my docking station at home (where I have a Dell 30" display)
to my docking station at work (where I have a Dell 24" display), and
actually have the new monitor be detected?  For at least the past
year, I have to reboot in order to be able to use the external
monitor?  This used to work, but it's been a very long-standing
regression.  I undrstand that Multi-stream DP is a evil horrible hack,
and supporting it is painful, but this used to work, and it hasn't in
a long time.  :-(

					- Ted