linux-kernel - Re: [PATCH REGRESSION v3] drm/panel: simple: restore connector

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Message-Id: <DF1F9S3FL5XG.1D9IAMJ5FHV4Z@bootlin.com>
Date: Thu, 18 Dec 2025 15:46:09 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Ludovic Desroches" <ludovic.desroches@...rochip.com>, "Neil Armstrong"
 <neil.armstrong@...aro.org>, "Jessica Zhang" <jesszhan0024@...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>, "Anusha
 Srivatsa" <asrivats@...hat.com>, "Jessica Zhang"
 <jessica.zhang@....qualcomm.com>
Cc: <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
 <stable@...r.kernel.org>
Subject: Re: [PATCH REGRESSION v3] drm/panel: simple: restore connector_type
 fallback

On Thu Dec 18, 2025 at 2:34 PM CET, Ludovic Desroches wrote:
> The switch from devm_kzalloc() + drm_panel_init() to
> devm_drm_panel_alloc() introduced a regression.
>
> Several panel descriptors do not set connector_type. For those panels,
> panel_simple_probe() used to compute a connector type (currently DPI as a
> fallback) and pass that value to drm_panel_init(). After the conversion
> to devm_drm_panel_alloc(), the call unconditionally used
> desc->connector_type instead, ignoring the computed fallback and
> potentially passing DRM_MODE_CONNECTOR_Unknown, which
> drm_panel_bridge_add() does not allow.
>
> Move the connector_type validation / fallback logic before the
> devm_drm_panel_alloc() call and pass the computed connector_type to
> devm_drm_panel_alloc(), so panels without an explicit connector_type
> once again get the DPI default.
>
> Signed-off-by: Ludovic Desroches <ludovic.desroches@...rochip.com>
> Fixes: de04bb0089a9 ("drm/panel/panel-simple: Use the new allocation in place of devm_kzalloc()")
> Cc: stable@...r.kernel.org

Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

Side note: this function is very long, it would be nice e.g. to move the
big mistake-checking switch (connector_type) to a function. Of course that
would be a separate series, after this fix is done.

Luca

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