Re: [Intel-gfx] [PATCH] drm/i915: Do a better job at disabling primary plane in the noatomic case.

[Ander Conselvan De Oliveira <conselvan2@gmail.com>]

On Thu, 2015-11-12 at 14:58 +0100, Maarten Lankhorst wrote:
> Op 12-11-15 om 14:37 schreef Ander Conselvan De Oliveira:
> > On Wed, 2015-11-11 at 15:36 +0100, Maarten Lankhorst wrote:
> > > When disable_noatomic is called plane_mask is not reliable yet,
> > > and plane_state->visible = true even after disabling the primary plane.
> > So the stale value of plane_state->visible causes a subsequent modeset to
> > enable
> > the primary again?
> Probably not because it would get recalculated in calc_changes, but it should
> really be set to false afterwards.

So basically I didn't understand how the wrong value of plane_state->visible
causes the bug that was mentioned. I think a brief explanation in the commit
message would be good.

> 
> in intel_plane_atomic_calc_changes:
> if (!was_crtc_enabled && WARN_ON(was_visible))
> was_visible = false;
> 
> and in intel_sanitize_crtc when intel_check_plane_mapping fails, it gets set
> to true to disable it.
> 
> This is really a special case and it's for disable_noatomic only. As the name
> says it can't rely on the atomic state.
> 
> > > Fix this by unsetting plane->visible if it was visible, and calling
> > > disable_planes with the primary plane as mask.
> > > 
> > > The other planes are already disabled in intel_sanitize_crtc, so
> > > they don't have to be handled here.
> > > 
> > > Cc: stable@vger.kernel.org #v4.3, v4.2?
> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92655
> > > Tested-by: Tomas Mezzadra <tmezzadra@gmail.com>
> > > Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_display.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > > b/drivers/gpu/drm/i915/intel_display.c
> > > index b5f7493213b7..bc3282ab5ed2 100644
> > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > @@ -6267,9 +6267,11 @@ static void intel_crtc_disable_noatomic(struct
> > > drm_crtc
> > > *crtc)
> > >  		WARN_ON(intel_crtc->unpin_work);
> > >  
> > >  		intel_pre_disable_primary(crtc);
> > > +
> > > +		intel_crtc_disable_planes(crtc, 1 << drm_plane_index(crtc
> > > ->primary));
> > > +		to_intel_plane_state(crtc->primary->state)->visible =
> > > false;
> > >  	}
> > >  
> > > -	intel_crtc_disable_planes(crtc, crtc->state->plane_mask);
> > Can't we just make plane_mask reliable? We know whether the primary plane is
> > enabled and all others were disabled prior to that. Or did I miss something.
> > 
> In the case of hardware readout you can't. The plane_mask gets set only if we
> can preserve the initial framebuffer
> else the primary plane gets disabled.

What I meant to say is that before a call to disable_noatomic but after we
disabled all other planes, plane_mask could have the appropriate value. As in we
could set plane_mask to 0 or drm_plane_index(primary) in readout_plane_state. It
would have to be update in disable_noatomic() though, the same way as 'visible'
is.

Anyway, I think the code is fine either way.

Ander