[PATCH] drm: bridge: panel: Register connector if DRM device is already registered

[Jagan Teki]

On Tue, Apr 19, 2022 at 11:08 PM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> On Tue, Apr 19, 2022 at 06:16:07PM +0200, Robert Foss wrote:
> > On Tue, 19 Apr 2022 at 11:41, Jagan Teki <jagan at amarulasolutions.com> wrote:
> > >
> > > On Tue, Apr 19, 2022 at 2:44 PM Marek Szyprowski
> > > <m.szyprowski at samsung.com> wrote:
> > > >
> > > > If panel_bridge_attach() happens after DRM device registration, the
> > > > created connector will not be registered by the DRM core anymore. Fix
> > > > this by registering it explicitely in such case.
> > > >
> > > > This fixes the following issue observed on Samsung Exynos4210-based Trats
> > > > board with a DSI panel (the panel driver is registed after the Exynos DRM
> > > > component device is bound):
> > > >
> > > > $ ./modetest -c -Mexynos
> > > > could not get connector 56: No such file or directory
> > > > Segmentation fault
> > > >
> > > > While touching this, move the connector reset() call also under the DRM
> > > > device registered check, because otherwise it is not really needed.
> > > >
> > > > Fixes: 934aef885f9d ("drm: bridge: panel: Reset the connector state pointer")
> > > > Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
> > > > ---
> > > > Here is a bit more backgroud on this issue is available in this thread:
> > > > https://lore.kernel.org/all/f0474a95-4ba3-a74f-d7de-ef7aab12bc86@samsung.com/
> > > > ---
> > > >  drivers/gpu/drm/bridge/panel.c | 7 +++++--
> > > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
> > > > index ff1c37b2e6e5..0ee563eb2b6f 100644
> > > > --- a/drivers/gpu/drm/bridge/panel.c
> > > > +++ b/drivers/gpu/drm/bridge/panel.c
> > > > @@ -83,8 +83,11 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
> > > >         drm_connector_attach_encoder(&panel_bridge->connector,
> > > >                                           bridge->encoder);
> > > >
> > > > -       if (connector->funcs->reset)
> > > > -               connector->funcs->reset(connector);
> > > > +       if (bridge->dev->registered) {
> > > > +               if (connector->funcs->reset)
> > > > +                       connector->funcs->reset(connector);
> > > > +               drm_connector_register(connector);
> > > > +       }
> > >
> > > Reviewed-by: Jagan Teki <jagan at amarulasolutions.com>
> >
> > Fixed typos in commit message.
> >
> > Reviewed-by: Robert Foss <robert.foss at linaro.org>
> >
> > Applied to drm-misc-next
>
> Doesn't this open the door to various race conditions ?
>
> Also, what happens if the panel bridge is detached and reattached ? If I

I believe the dev->registered is the check for those already registered.

Jagan.