[PATCH v1] drm: Do not allow to set NOFB for active primary plane

[Lisovskiy, Stanislav]

On Mon, 2019-04-15 at 15:36 +0300, Ville Syrjälä wrote:
> On Mon, Apr 15, 2019 at 10:58:47AM +0300, Stanislav Lisovskiy wrote:
> > There was an issue reported from end users, confirmed
> > also locally that when user executes xrandr --output <some DP>
> > --rotate left/right, the other eDP screen gets blank after
> > rotation.
> > 
> > Investigation showed that reason was that primary plane
> > was that screen was for some reason disabled, while cursor
> > plane was still enabled.
> > After some effort it turns out that userspace might wrongly
> > assign NOFB to active primary plane for some reason.
> > 
> > Then this gets detected in drm_atomic_helper_check_plane_state,
> > called from ->plane_check and plane gets deactivated, leaving
> > the screen blank and cursor visible. This can be cured by reboot
> > or xrandr off/on sequence for that crtc.
> > 
> > This patch is proposal to fix the issue by forbiding fb removal
> > from active primary plane. If one needs to remove fb plane must be
> > disabled first.
> > 
> > Not sure if this is correct, however it fixes the issue at least.
> 
> It is not. Removing the fb (and crtc) is how you disable a plane.

Ok, most likely this should be fixed in userspace then. As what I see
is that it removes FB from the primary plane for eDP, once we rotate
the other screen(why?), which is then turned off
in drm_atomic_helper_check_plane_state(!fb check) and then we have this
nice blank screen which you saw. If I prevent it somehow, theneverything works fine, however the origin of a problem seems to be in userspace.

> 
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110375
> > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> > ---
> >  drivers/gpu/drm/drm_atomic_uapi.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_uapi.c
> > b/drivers/gpu/drm/drm_atomic_uapi.c
> > index ea797d4c82ee..e2f078b302f3 100644
> > --- a/drivers/gpu/drm/drm_atomic_uapi.c
> > +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> > @@ -229,6 +229,15 @@ drm_atomic_set_fb_for_plane(struct
> > drm_plane_state *plane_state,
> >  {
> >  	struct drm_plane *plane = plane_state->plane;
> >  
> > +	if (!fb) {
> > +		if (plane->state->visible && plane->type ==
> > DRM_PLANE_TYPE_PRIMARY) {a
> 
> .visible is not even computed yet when this is called.
> 
> > +			DRM_DEBUG_ATOMIC("Not allowed to set [NOFB] for
> > active"
> > +					" primary [PLANE:%d:%s] -
> > disable first",
> > +					plane->base.id, plane->name);
> > +			return;
> > +		}
> > +	}
> > +
> >  	if (fb)
> >  		DRM_DEBUG_ATOMIC("Set [FB:%d] for [PLANE:%d:%s] state
> > %p\n",
> >  				 fb->base.id, plane->base.id, plane-
> > >name,
> > -- 
> > 2.17.1
> > 
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> 
>