linux-kernel - Re: [PATCH] drm: tda998x: mali-dp: hdlcd: refactor connector registration

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Message-ID: <20161031085843.GU1041@n2100.armlinux.org.uk>
Date:   Mon, 31 Oct 2016 08:58:43 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Brian Starkey <brian.starkey@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm: tda998x: mali-dp: hdlcd: refactor connector
 registration

On Mon, Oct 24, 2016 at 10:24:42PM +0200, Daniel Vetter wrote:
> On Mon, Oct 24, 2016 at 4:52 PM, Brian Starkey <brian.starkey@....com> wrote:
> >>
> >>> diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c
> >>> b/drivers/gpu/drm/i2c/tda998x_drv.c
> >>> index f4315bc..6e6fca2 100644
> >>> --- a/drivers/gpu/drm/i2c/tda998x_drv.c
> >>> +++ b/drivers/gpu/drm/i2c/tda998x_drv.c
> >>> @@ -1369,7 +1369,6 @@ const struct drm_connector_helper_funcs
> >>> tda998x_connector_helper_funcs = {
> >>>
> >>>  static void tda998x_connector_destroy(struct drm_connector *connector)
> >>>  {
> >>> -       drm_connector_unregister(connector);
> >>>         drm_connector_cleanup(connector);
> >>>  }
> >>>
> >>> @@ -1441,16 +1440,10 @@ static int tda998x_bind(struct device *dev,
> >>> struct device *master, void *data)
> >>>         if (ret)
> >>>                 goto err_connector;
> >>>
> >>> -       ret = drm_connector_register(&priv->connector);
> >>> -       if (ret)
> >>> -               goto err_sysfs;
> >>> -
> >>
> >>
> >> Instead of smashing all these patches into one, what about checking here
> >> for midlayer driver set with:
> >>
> >>         /* register here for drivers still using midlayer load/unload */
> >>         if (dev->driver->load)
> >>                 drm_connector_register(connector),
> >>
> >> Similar in other places. That way we wouldn't need to switch the world in
> >> one patch.
> >
> >
> > I don't think that helps. If we do that in isolation (first), then
> > mali-dp and hdlcd won't get their connectors registered because their
> > bind order is:
> >
> >         drm_dev_register();
> >         component_bind_all();
> >
> > If we change the mali-dp/hdlcd bind order first, then tda998x will
> > explode on drm_connector_register() until it's patched to remove that.
> >
> > As I mentioned in my mail to Russell, the only way I can see to avoid
> > patching all three drivers in one go is:
> >  1) Add (probably open-coded) drm_connector_register_all() to the end
> >     of bind in hdlcd and mali-dp
> >  2) Patch tda998x to remove drm_connector_register()
> >  3) Reorder hdlcd/mali-dp bind and remove the connector registration
> >     added in 1)
> >
> > We can do that, but it's extra churn for the same result, and none of
> > the 5 patches will really make sense in isolation anyway.
> 
> I thought there's also armada to take care of, which this patch would
> break?

NO NO NO NO NO.  I've said this several times.  Let's try it again,
and see if it sticks.

Because Armada has not been converted from a mid-layered driver, it
is _IMMUNE_ from any patch removing the drm_connector_register() call
in TDA998x.  It does _NOT_ break in any way.

Only those drivers which are de-mid-layered, and worked around the
drm_connector_register() call inside TDA998x (eg, mali) break, because
of the order in which they are _forced_ to call stuff.

In a de-mid-layered driver, with the drm_connector_register() call in
place in TDA998x, drm_dev_register() _MUST_ be called prior to
component_bind_all(), otherwise you get a WARN_ON() dump from the
kobject code.  With the drm_connector_register() call removed,
drm_dev_register() _MUST_ be called after component_bind_all() so that
the connector is registered.

It's the de-mid-layered drivers which are the problem here, not the
mid-layered ones like Armada.

> Maybe even another driver, so the hack would still be useful
> for those other drivers. And it would have been useful if malidp/hdlcd
> wouldn't have started out with the wrong init ordering ;-)

It's forced into the "wrong init ordering" due to the kobject WARN_ON.

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