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

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Message-ID: <3fc2574a-be4c-4273-82b5-317d822b3767@microchip.com>
Date: Wed, 26 Nov 2025 07:27:17 +0000
From: <Ludovic.Desroches@...rochip.com>
To: <dmitry.baryshkov@....qualcomm.com>
CC: <neil.armstrong@...aro.org>, <jesszhan0024@...il.com>,
	<maarten.lankhorst@...ux.intel.com>, <mripard@...nel.org>,
	<tzimmermann@...e.de>, <airlied@...il.com>, <simona@...ll.ch>,
	<asrivats@...hat.com>, <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 11/21/25 23:52, Dmitry Baryshkov wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> 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.

I don’t have a strong opinion on this point. I don’t know if there are 
any historical reasons behind all this.

Regards,
Ludovic

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