linux-kernel - Re: [PATCH v5] drm/bridge: imx8qxp-pixel-link: get/put the next bridge

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Message-ID: <8d8e678b-bd3f-441e-9496-e1461a1289ea@nxp.com>
Date: Wed, 4 Feb 2026 14:27:31 +0800
From: Liu Ying <victor.liu@....com>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>,
 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>,
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>, Ian Ray <ian.ray@...ealthcare.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 dri-devel@...ts.freedesktop.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] drm/bridge: imx8qxp-pixel-link: get/put the next
 bridge

Hi Luca,

On Tue, Feb 03, 2026 at 11:35:25AM +0100, Luca Ceresoli wrote:
> This driver obtains a bridge pointer from of_drm_find_bridge() in the probe
> function and stores it until driver removal. of_drm_find_bridge() is
> deprecated. Move to of_drm_find_and_get_bridge() for the bridge to be
> refcounted and use bridge->next_bridge to put the reference on
> deallocation.
> 
> To keep the code as simple and reliable as possible, get a reference for
> each pointer that stores a drm_bridge address when it is stored and release
> it when the pointer is overwritten or goes out of scope. Also remove the
> intermediate selected_bridge variable to reduce the refcounted variables in
> the function. The involved pointers are:
> 
>  * next_bridge loop-local variable:
>    - get reference by of_drm_find_and_get_bridge()
>    - put reference at the end of the loop iteration (__free)
> 
>  * pl->bridge.next_bridge, tied to struct imx8qxp_pixel_link lifetime:
>    - get reference when assigned (by copy from next_bridge)
>    - put reference before reassignment if reassignment happens
>    - put reference when the struct imx8qxp_pixel_link embedding the
>      struct drm_bridge is destroyed (struct drm_bridge::next_bridge)
> 
> Additionally, split the somewhat complex if() for readability.
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> 
> ---
> 
> Changes in v5:
> - rewrite commit message after Liu's review to clarify the per-pointer
>   get/put idea
> - split the if()s involved in selcting the bridge
> - remove intermediate selected_bridge pointer
> - removed Maxime's R-by, patch changed
> ---
>  drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c b/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
> index 91e4f4d55469..e29e099b893a 100644
> --- a/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
> +++ b/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
> @@ -23,7 +23,6 @@
>  
>  struct imx8qxp_pixel_link {
>  	struct drm_bridge bridge;
> -	struct drm_bridge *next_bridge;
>  	struct device *dev;
>  	struct imx_sc_ipc *ipc_handle;
>  	u8 stream_id;
> @@ -140,7 +139,7 @@ static int imx8qxp_pixel_link_bridge_attach(struct drm_bridge *bridge,
>  	}
>  
>  	return drm_bridge_attach(encoder,
> -				 pl->next_bridge, bridge,
> +				 pl->bridge.next_bridge, bridge,
>  				 DRM_BRIDGE_ATTACH_NO_CONNECTOR);
>  }
>  
> @@ -260,7 +259,6 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
>  {
>  	struct device_node *np = pl->dev->of_node;
>  	struct device_node *port;
> -	struct drm_bridge *selected_bridge = NULL;
>  	u32 port_id;
>  	bool found_port = false;
>  	int reg;
> @@ -297,7 +295,8 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
>  			continue;
>  		}
>  
> -		struct drm_bridge *next_bridge = of_drm_find_bridge(remote);
> +		struct drm_bridge *next_bridge __free(drm_bridge_put) =
> +			of_drm_find_and_get_bridge(remote);
>  		if (!next_bridge)
>  			return -EPROBE_DEFER;
>  
> @@ -305,12 +304,16 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
>  		 * Select the next bridge with companion PXL2DPI if
>  		 * present, otherwise default to the first bridge
>  		 */
> -		if (!selected_bridge || of_property_present(remote, "fsl,companion-pxl2dpi"))
> -			selected_bridge = next_bridge;
> +		if (!pl->bridge.next_bridge)
> +			pl->bridge.next_bridge = drm_bridge_get(next_bridge);
> +
> +		if (of_property_present(remote, "fsl,companion-pxl2dpi")) {
> +			drm_bridge_put(pl->bridge.next_bridge);
> +			pl->bridge.next_bridge = drm_bridge_get(next_bridge);
> +		}

Can you drop the intermediate next_bridge variable to simplify the code?

-8<-
if (!pl->bridge.next_bridge) {
        pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
        if (!pl->bridge.next_bridge)
                return -EPROBE_DEFER;
}

if (of_property_present(remote, "fsl,companion-pxl2dpi")) {
        drm_bridge_put(pl->bridge.next_bridge);
        pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
        if (!pl->bridge.next_bridge)
                return -EPROBE_DEFER;
}
-8<-

>  	}
>  
>  	pl->mst_addr = port_id - 1;
> -	pl->next_bridge = selected_bridge;
>  
>  	return 0;
>  }
> 

-- 
Regards,
Liu Ying