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

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Message-ID: <4am5nvb4ldzvvaavkdu2o36viltoxxyxwybrmj3h35wtdhfcpa@53t4zahc3y6c>
Date: Sat, 22 Nov 2025 00:52:46 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Ludovic Desroches <ludovic.desroches@...rochip.com>
Cc: 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>,
        Luca Ceresoli <luca.ceresoli@...tlin.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH REGRESSION] drm/panel: simple: restore connector_type
 fallback

On Fri, Nov 21, 2025 at 02:20:48PM +0100, 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()")
> ---
> Hi,
> 
> I am not sure whether this regression has already been reported or
> addressed. If it has, please feel free to drop this patch.

Would it be better to fix those panels instead? In the end, the panel
usually has only one bus.

> ---
>  drivers/gpu/drm/panel/panel-simple.c | 86 ++++++++++++++++++------------------
>  1 file changed, 43 insertions(+), 43 deletions(-)

-- 
With best wishes
Dmitry