Re: [PATCH][next] drm/rockchip: Remove redundant assignment of pointer connector

[Alex Bee]

Hi all,

Am 22.09.21 um 19:31 schrieb Alex Bee:
> Hi Heiko,
>
> Am 22.09.21 um 18:45 schrieb Heiko Stübner:
> > Hi Alex,
> >
> > Am Mittwoch, 22. September 2021, 18:35:38 CEST schrieb Alex Bee:
> > > Hi Colin,
> > > Am 22.09.21 um 13:24 schrieb Colin King:
> > > > From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> > > >
> > > > The pointer connector is being assigned a value that is never
> > > > read, it is being updated immediately afterwards. The assignment
> > > > is redundant and can be removed.
> > > The pointer to the connector is used in rockchip_rgb_fini for
> > > drm_connector_cleanup.
> > > It's pretty much the same for the encoder, btw.
> > I think the issue is more the two lines
> >
> >     connector = &rgb->connector;
> >       connector = drm_bridge_connector_init(rgb->drm_dev, encoder);
> >
> > hence the connector = &rgb->connector being overwritten immediately 
> > after
> >
> > Now that I look at it again, the whole approach looks strange.
> > drm_bridge_connector_init() creates the connector structure and
> > returns a pointer to it.
>
> Totally agreed.
>
> The main reason I was doing it that way, was the way it was done 
> already in rockchip_lvds.c, where the connector was already existent 
> in the struct rockchip_lvds (and was already used in the panel-case - 
> all places where it is used accept pointers also, btw) and is *no* 
> pointer - and is done already this very strange way.
>
> I wanted to re-use it for the bridge-case and didn't want to differ in 
> coding in rockchip-rgb to much.
>
> The only reason I can think of, why it was done that way is, that we 
> might need a pointer to a fully initialized struct drm_connector for 
> some reason (drm_connector_cleanup ?), what we wouldn't have if have 
> just a pointer and something goes wrong before drm_connector_init 
> respectivly drm_bridge_connector_init.
>
> Alex
>
>
> > So the first line below sets the connector pointer to point to the
> > &rgb->connector element and the second line then set a completely
> > different address into it.
> >
> > So the connector element in rockchip_lvds and rockchip_rgb should 
> > actually
> > become a pointer itself to hold the connector element returned from
> > drm_bridge_connector_init() .
It turns out, nothing bad happens (i.e. rockchip_rgb_fini, the only 
place where the connector is also used, isn't called if 
rockchip_rgb_init fails) - so it will be OK if we make the connector a 
pointer in struct rockchip_rgb. But we'll need to keep it a "full" 
struct drm_connector in struct rockchip_lvds, since in case it's a 
panel  it gets properties assigend before drm_connector_init is called 
and should for that reason initialized before.

I'll send a patch soon.

Alex

> > Heiko
> >
> > > Regards,
> > >
> > > Alex
> > > > Addresses-Coverity: ("Unused value")
> > > > Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> > > > ---
> > > >    drivers/gpu/drm/rockchip/rockchip_rgb.c | 1 -
> > > >    1 file changed, 1 deletion(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/rockchip/rockchip_rgb.c 
> > > > b/drivers/gpu/drm/rockchip/rockchip_rgb.c
> > > > index 09be9678f2bd..18fb84068a64 100644
> > > > --- a/drivers/gpu/drm/rockchip/rockchip_rgb.c
> > > > +++ b/drivers/gpu/drm/rockchip/rockchip_rgb.c
> > > > @@ -150,7 +150,6 @@ struct rockchip_rgb *rockchip_rgb_init(struct 
> > > > device *dev,
> > > >        if (ret)
> > > >            goto err_free_encoder;
> > > >    -    connector = &rgb->connector;
> > > >        connector = drm_bridge_connector_init(rgb->drm_dev, encoder);
> > > >        if (IS_ERR(connector)) {
> > > >            DRM_DEV_ERROR(drm_dev->dev,