Re: [PATCH v7 1/5] drm/atomic_helper: Disallow new modesets on unregistered connectors

[Daniel Vetter]

On Tue, Oct 09, 2018 at 08:20:27PM +0300, Ville Syrjälä wrote:
> On Mon, Oct 08, 2018 at 07:24:30PM -0400, Lyude Paul wrote:
> > With the exception of modesets which would switch the DPMS state of a
> > connector from on to off, we want to make sure that we disallow all
> > modesets which would result in enabling a new monitor or a new mode
> > configuration on a monitor if the connector for the display in question
> > is no longer registered. This allows us to stop userspace from trying to
> > enable new displays on connectors for an MST topology that were just
> > removed from the system, without preventing userspace from disabling
> > DPMS on those connectors.
> > 
> > Changes since v5:
> > - Fix typo in comment, nothing else
> > 
> > Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> >  drivers/gpu/drm/drm_atomic_helper.c | 21 ++++++++++++++++++++-
> >  1 file changed, 20 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 6f66777dca4b..e6a2cf72de5e 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -319,6 +319,26 @@ update_connector_routing(struct drm_atomic_state *state,
> >  		return 0;
> >  	}
> >  
> > +	crtc_state = drm_atomic_get_new_crtc_state(state,
> > +						   new_connector_state->crtc);
> > +	/*
> > +	 * For compatibility with legacy users, we want to make sure that
> > +	 * we allow DPMS On->Off modesets on unregistered connectors. Modesets
> > +	 * which would result in anything else must be considered invalid, to
> > +	 * avoid turning on new displays on dead connectors.
> > +	 *
> > +	 * Since the connector can be unregistered at any point during an
> > +	 * atomic check or commit, this is racy. But that's OK: all we care
> > +	 * about is ensuring that userspace can't do anything but shut off the
> > +	 * display on a connector that was destroyed after its been notified,
> > +	 * not before.
> > +	 */
> > +	if (!READ_ONCE(connector->registered) && crtc_state->active) {
> > +		DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] is not registered\n",
> > +				 connector->base.id, connector->name);
> > +		return -EINVAL;
> > +	}
> 
> This broke my ilk (and presumably snb-bdw as well).
> 
> [   25.593121] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]] Updating routing for [CONNECTOR:55:eDP-1]
> [   25.593131] [drm:drm_atomic_helper_check_modeset [drm_kms_helper]] [CONNECTOR:55:eDP-1] is not registered
> [   25.593133] ------------[ cut here ]------------
> [   25.593134] Could not determine valid watermarks for inherited state
> [   25.593212] WARNING: CPU: 0 PID: 3060 at ../drivers/gpu/drm/i915/intel_display.c:14983 intel_modeset_init+0x12cf/0x1980 [i915]
> 
> Also I can't see that any of the repostings of this has undergone the
> full CI run (just BAT results are visible). Not sure why that is.
> Not that the full run would have caught this because we unwisely 
> load the module before the tests start. Which means any failures
> during initial readout/takeover will not be flagged :(

Ugh, so we need a special bool for "unplugged", to differentiate it from
the "it's real, but not yet registered because the driver isn't fully
loaded yet" case.
-Daniel

> 
> > +
> >  	funcs = connector->helper_private;
> >  
> >  	if (funcs->atomic_best_encoder)
> > @@ -363,7 +383,6 @@ update_connector_routing(struct drm_atomic_state *state,
> >  
> >  	set_best_encoder(state, new_connector_state, new_encoder);
> >  
> > -	crtc_state = drm_atomic_get_new_crtc_state(state, new_connector_state->crtc);
> >  	crtc_state->connectors_changed = true;
> >  
> >  	DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] using [ENCODER:%d:%s] on [CRTC:%d:%s]\n",
> > -- 
> > 2.17.1
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Ville Syrjälä
> Intel

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