linux-kernel - Re: [PATCH v2 3/3] drm/display: bridge_connector: get/put the panel

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Message-ID: <8725fc5b-4d29-4fa5-9227-6755fdd9a2e0@bootlin.com>
Date: Thu, 30 Oct 2025 15:54:38 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 Naresh Kamboju <naresh.kamboju@...aro.org>,
 Andrzej Hajda <andrzej.hajda@...el.com>,
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] drm/display: bridge_connector: get/put the
 panel_bridge



Le 17/10/2025 à 18:15, Luca Ceresoli a écrit :
> The panel_bridge pointer is taken inside the loop and used after the
> loop. Being a local variable, use a cleanup action to ensure it is put on
> return.
> 
> Based on the code structure the panel_bridge pointer might be assigned
> during multiple loop iterations. Even though this is probably not possible
> in the practice, ensure there is no reference leak by putting the reference
> to the old value before overwriting with the new value.
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

Reviewed-by: Louis Chauvet <louis.chauvet@...tlin.com>

> ---
> 
> This patch was added in v2:
> - taking the panel_bridge specific code from the original (buggy) patch,
>    and split it for clarity from the larger patch covering stored bridge
>    pointers
> - comapred to the original code, added drm_bridge_put() for extra safety
>    even though likely not necessary
> ---
>   drivers/gpu/drm/display/drm_bridge_connector.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c b/drivers/gpu/drm/display/drm_bridge_connector.c
> index 95ccf86527129edaa6fcc75c6202985e73c46da8..a2d30cf9e06df44b89456b5aba8198ee1e5d5601 100644
> --- a/drivers/gpu/drm/display/drm_bridge_connector.c
> +++ b/drivers/gpu/drm/display/drm_bridge_connector.c
> @@ -652,7 +652,7 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
>   	struct drm_bridge_connector *bridge_connector;
>   	struct drm_connector *connector;
>   	struct i2c_adapter *ddc = NULL;
> -	struct drm_bridge *panel_bridge = NULL;
> +	struct drm_bridge *panel_bridge __free(drm_bridge_put) = NULL;
>   	unsigned int supported_formats = BIT(HDMI_COLORSPACE_RGB);
>   	unsigned int max_bpc = 8;
>   	bool support_hdcp = false;
> @@ -787,8 +787,10 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
>   		if (bridge->ddc)
>   			ddc = bridge->ddc;
>   
> -		if (drm_bridge_is_panel(bridge))
> -			panel_bridge = bridge;
> +		if (drm_bridge_is_panel(bridge)) {
> +			drm_bridge_put(panel_bridge);
> +			panel_bridge = drm_bridge_get(bridge);
> +		}
>   
>   		if (bridge->support_hdcp)
>   			support_hdcp = true;
> 

-- 
--
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com