linux-kernel - Re: [PATCH 3/5] drm/panel: Add attach/detach callbacks

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Message-ID: <CAGAzgsqkJnc4jESSVMtYEQ4=DhmLVKbo_8CTk9cwH0j+55ZuTw@mail.gmail.com>
Date:   Fri, 21 Jun 2019 18:54:57 -0700
From:   "dbasehore ." <dbasehore@...omium.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        CK Hu <ck.hu@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree@...r.kernel.org,
        Intel Graphics <intel-gfx@...ts.freedesktop.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 3/5] drm/panel: Add attach/detach callbacks

On Fri, Jun 21, 2019 at 2:19 AM Thierry Reding <thierry.reding@...il.com> wrote:
>
> On Tue, Jun 11, 2019 at 05:25:47PM -0700, dbasehore . wrote:
> > On Tue, Jun 11, 2019 at 1:57 AM Daniel Vetter <daniel@...ll.ch> 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 <dbasehore@...omium.org>
> > > > ---
> > > >  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.

For now, I'll just put width, height, bpc, orientation, bus_flags, and
bus_formats in the drm_panel struct. Those are pretty consistently set
from either get_modes or prepare. The other thing those all have in
common is that the values don't change.

We could just add an entire drm_display_info struct inside drm_panel,
but I don't know if we can just copy that over or set a pointer
without breaking something else, since some of the values in the
drm_display_info struct are not set by the panel (but maybe set by
something else).

>
> 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

Thanks for the review