Re: [PATCH v3 2/3] drm/vc4: dsi: stop using deprecated drmm_of_get_bridge()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] drm/vc4: reference leak of next_bridge on component unbind/rebind
--

commit 01a94378aeae8cb42a9f68ed6384a34ccaa162a0
Author: Luca Ceresoli <luca.ceresoli@bootlin.com>

drm/vc4: dsi: stop using deprecated drmm_of_get_bridge()

drmm_of_get_bridge() is deprecated, switch to
of_drm_get_bridge_by_endpoint(). As of_drm_get_bridge_by_endpoint() returns
a refcounted bridge, ensure it is put by using bridge.next_bridge.

> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index 0148f2befed14..675bd0fc13913 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
[ ... ]
> @@ -1775,9 +1774,13 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
>  	if (ret)
>  		return ret;
>  
> +	dsi->bridge.next_bridge = drm_bridge_get(next_bridge);
> +

[Severity: Medium]
Does this code introduce a regression that leaks the bridge reference across
component unbind/rebind cycles?

During component unbind, vc4_dsi_release_action() only drops the reference
to dsi->bridge acquired during bind:

static void vc4_dsi_release_action(struct drm_device *drm, void *ptr)
{
	struct vc4_dsi *dsi = ptr;

	drm_bridge_put(&dsi->bridge);
}

Because dsi->bridge outlives the component unbind, __drm_bridge_free() is
not executed, and the reference to next_bridge is not automatically released.

When the component is subsequently rebound, vc4_dsi_bind() overwrites
dsi->bridge.next_bridge here without freeing the previous pointer,
permanently leaking the bridge reference. Does next_bridge need to be
explicitly cleared in the teardown path?

>  	ret = drm_bridge_attach(encoder, &dsi->bridge, NULL, 0);
> -	if (ret)
> +	if (ret) {
> +		drm_bridge_clear_and_put(&dsi->bridge.next_bridge);
>  		return ret;
> +	}
>  
>  	return 0;
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261013-drm-fix-of_get_bridge-build-regression-v3-0-0b4c0b65be82@bootlin.com?part=2