Subject: Re: [PATCH 3/5] drm/panel: Add attach/detach callbacks

From: Thierry Reding <[email-masked]>
Date: Fri, 21 Jun 2019 11:19:28 +0200

On Tue, Jun 11, 2019 at 05:25:47PM -0700, dbasehore . wrote:
> On Tue, Jun 11, 2019 at 1:57 AM Daniel Vetter <[email-masked]> wrote:
> >
> > On Mon, Jun 10, 2019 at 09:03:48PM -0700, Derek Basehore wrote:
> > > This adds the attach/detach callbacks. These are for setting up
> > > internal state for the connector/panel pair that can't be done at
> > > probe (since the connector doesn't exist) and which don't need to be
> > > repeatedly done for every get/modes, prepare, or enable callback.
> > > Values such as the panel orientation, and display size can be filled
> > > in for the connector.
> > >
> > > Signed-off-by: Derek Basehore <[email-masked]>
> > > ---
> > >  drivers/gpu/drm/drm_panel.c | 14 ++++++++++++++
> > >  include/drm/drm_panel.h     |  4 ++++
> > >  2 files changed, 18 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> > > index 3b689ce4a51a..72f67678d9d5 100644
> > > --- a/drivers/gpu/drm/drm_panel.c
> > > +++ b/drivers/gpu/drm/drm_panel.c
> > > @@ -104,12 +104,23 @@ EXPORT_SYMBOL(drm_panel_remove);
> > >   */
> > >  int drm_panel_attach(struct drm_panel *panel, struct drm_connector *connector)
> > >  {
> > > +     int ret;
> > > +
> > >       if (panel->connector)
> > >               return -EBUSY;
> > >
> > >       panel->connector = connector;
> > >       panel->drm = connector->dev;
> > >
> > > +     if (panel->funcs->attach) {
> > > +             ret = panel->funcs->attach(panel);
> > > +             if (ret < 0) {
> > > +                     panel->connector = NULL;
> > > +                     panel->drm = NULL;
> > > +                     return ret;
> > > +             }
> > > +     }
> >
> > Why can't we just implement this in the drm helpers for everyone, by e.g.
> > storing a dt node in drm_panel? Feels a bit overkill to have these new
> > hooks here.
> >
> > Also, my understanding is that this dt stuff is supposed to be
> > standardized, so this should work.
> 
> So do you want all of this information added to the drm_panel struct?
> If we do that, we don't necessarily even need the drm helper function.
> We could just copy the values over here in the drm_panel_attach
> function (and clear them in drm_panel_detach).

Yeah, I think we should have all this extra information in the struct
drm_panel. However, I think we need to more carefully split things such
that the DT parsing happens at panel probe time. That way we can catch
errors in DT, or missing entries/resources when we can still do
something about it.

If we start parsing DT and encounter failures, it's going to be very
confusing if that's at panel attach time where code will usually just
assume that everything is already validated and can't fail anymore.

Thierry
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