linux-kernel - Re: [PATCH v5 20/25] drm/tilcdc: Use devm_drm_of_get

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Message-Id: <DG269FV5MZ8I.2VFNJXA0N2Y26@bootlin.com>
Date: Fri, 30 Jan 2026 20:31:11 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Kory Maincent (TI.com)" <kory.maincent@...tlin.com>, "Jyri Sarha"
 <jyri.sarha@....fi>, "Tomi Valkeinen" <tomi.valkeinen@...asonboard.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>, "Rob
 Herring" <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>,
 "Conor Dooley" <conor+dt@...nel.org>, "Russell King"
 <linux@...linux.org.uk>, "Bartosz Golaszewski" <brgl@...ev.pl>, "Tony
 Lindgren" <tony@...mide.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>
Cc: "Markus Schneider-Pargmann" <msp@...libre.com>, "Bajjuri Praneeth"
 <praneeth@...com>, "Louis Chauvet" <louis.chauvet@...tlin.com>, "Thomas
 Petazzoni" <thomas.petazzoni@...tlin.com>, "Miguel Gazquez"
 <miguel.gazquez@...tlin.com>, "Herve Codina" <herve.codina@...tlin.com>,
 <dri-devel@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
 <linux-omap@...r.kernel.org>
Subject: Re: [PATCH v5 20/25] drm/tilcdc: Use devm_drm_of_get_bridge()
 helper

Hi Kory,

On Fri Jan 23, 2026 at 5:12 PM CET, Kory Maincent (TI.com) wrote:
> Replace drm_of_find_panel_or_bridge() with the newer
> devm_drm_of_get_bridge() helper which simplifies the code by:
> - Automatically handling both panel and bridge cases internally
> - Managing the panel-to-bridge conversion when needed
> - Using devres for resource management, eliminating manual cleanup
>
> This removes the need for explicit panel-to-bridge conversion via
> devm_drm_panel_bridge_add_typed() and the associated error handling path.
>
> Signed-off-by: Kory Maincent (TI.com) <kory.maincent@...tlin.com>

I'm OK with this patch, based on the v4 discussion. I have a question
however, see below.

> --- a/drivers/gpu/drm/tilcdc/tilcdc_encoder.c
> +++ b/drivers/gpu/drm/tilcdc/tilcdc_encoder.c
> @@ -55,15 +55,12 @@ int tilcdc_encoder_create(struct drm_device *ddev)
>  	struct tilcdc_drm_private *priv = ddev_to_tilcdc_priv(ddev);
>  	struct tilcdc_encoder *encoder;
>  	struct drm_bridge *bridge;
> -	struct drm_panel *panel;
> -	int ret;
>
> -	ret = drm_of_find_panel_or_bridge(ddev->dev->of_node, 0, 0,
> -					  &panel, &bridge);
> -	if (ret == -ENODEV)
> +	bridge = devm_drm_of_get_bridge(ddev->dev, ddev->dev->of_node, 0, 0);
> +	if (PTR_ERR(bridge) == -ENODEV)
>  		return 0;
> -	else if (ret)
> -		return ret;
> +	else if (IS_ERR(bridge))
> +		return PTR_ERR(bridge);
>
>  	encoder = drmm_simple_encoder_alloc(ddev, struct tilcdc_encoder,
>  					    base, DRM_MODE_ENCODER_NONE);
> @@ -73,12 +70,5 @@ int tilcdc_encoder_create(struct drm_device *ddev)
>  	}
>  	priv->encoder = encoder;
>
> -	if (panel) {
> -		bridge = devm_drm_panel_bridge_add_typed(ddev->dev, panel,
> -							 DRM_MODE_CONNECTOR_DPI);

You are introducing a subtle difference here: while you pass the connector
type to devm_drm_panel_bridge_add_typed(), devm_drm_of_get_bridge() does
not take it and expects it to ahve been set previously and errors out if it
hasn't.

Can you ensure the connector type is alway set before this
devm_drm_of_get_bridge() call?

All the changes to the driver in the previous patches of this series make
it hard to find that out from here.

Luca

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