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

From: Alex Bee
Date: Wed Sep 22 2021 - 15:20:17 EST


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,