Re: [PATCH 2/2] drm/atomic: clear new_state pointers at hw_done

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Nov 01, 2019 at 12:49:02PM -0700, Rob Clark wrote:
> On Fri, Nov 1, 2019 at 12:25 PM Ville Syrjälä
> <ville.syrjala@linux.intel.com> wrote:
> >
> > On Fri, Nov 01, 2019 at 11:07:13AM -0700, Rob Clark wrote:
> > > From: Rob Clark <robdclark@chromium.org>
> > >
> > > The new state should not be accessed after this point.  Clear the
> > > pointers to make that explicit.
> > >
> > > This makes the error corrected in the previous patch more obvious.
> > >
> > > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > > ---
> > >  drivers/gpu/drm/drm_atomic_helper.c | 29 +++++++++++++++++++++++++++++
> > >  1 file changed, 29 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > > index 732bd0ce9241..176831df8163 100644
> > > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > > @@ -2234,13 +2234,42 @@ EXPORT_SYMBOL(drm_atomic_helper_fake_vblank);
> > >   */
> > >  void drm_atomic_helper_commit_hw_done(struct drm_atomic_state *old_state)
> > >  {
> > > +     struct drm_connector *connector;
> > > +     struct drm_connector_state *old_conn_state, *new_conn_state;
> > >       struct drm_crtc *crtc;
> > >       struct drm_crtc_state *old_crtc_state, *new_crtc_state;
> > > +     struct drm_plane *plane;
> > > +     struct drm_plane_state *old_plane_state, *new_plane_state;
> > >       struct drm_crtc_commit *commit;
> > > +     struct drm_private_obj *obj;
> > > +     struct drm_private_state *old_obj_state, *new_obj_state;
> > >       int i;
> > >
> > > +     /*
> > > +      * After this point, drivers should not access the permanent modeset
> > > +      * state, so we also clear the new_state pointers to make this
> > > +      * restriction explicit.
> > > +      *
> > > +      * For the CRTC state, we do this in the same loop where we signal
> > > +      * hw_done, since we still need to new_crtc_state to fish out the
> > > +      * commit.
> > > +      */
> > > +
> > > +     for_each_oldnew_connector_in_state(old_state, connector, old_conn_state, new_conn_state, i) {
> > > +             old_state->connectors[i].new_state = NULL;
> > > +     }
> > > +
> > > +     for_each_oldnew_plane_in_state(old_state, plane, old_plane_state, new_plane_state, i) {
> > > +             old_state->planes[i].new_state = NULL;
> > > +     }
> > > +
> > > +     for_each_oldnew_private_obj_in_state(old_state, obj, old_obj_state, new_obj_state, i) {
> > > +             old_state->private_objs[i].new_state = NULL;
> > > +     }
> > > +
> > >       for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
> > >               old_state->crtcs[i].new_self_refresh_active = new_crtc_state->self_refresh_active;
> > > +             old_state->crtcs[i].new_state = NULL;
> >
> > That's going to be a real PITA when doing programming after the fact from
> > a vblank worker. It's already a pain that the new_crtc_state->state is
> > getting NULLed somewhere.
> >
> 
> I think you already have that problem, this just makes it explicit.

I don't yet. Except on a branch where I have my vblank workers.
And I think the only problem is having the helpers/core clobber
the pointers when it should not. I don't see why it can't just
leave them be and let me use them.

-- 
Ville Syrjälä
Intel