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

["Luca Ceresoli" <luca.ceresoli@bootlin.com>]

On Tue Oct 13, 2026 at 5:35 PM CEST, sashiko-bot wrote:
> 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?

Ah, right. I'm fixing this in v4 by calling
drm_bridge_clear_and_put(&dsi->bridge.next_bridge).

Not sure adding it to vc4_dsi_release_action() would be correct in case of
unbind/rebind, so I'm probably adding a new vc4_dsi_unbind() for that.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com