linux-kernel - Re: [PATCH] drm/bridge-connector: select DRM_DISPLAY_HELPER from DRM_BRIDGE

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Message-Id: <19944f9b-e7d7-45da-bf1c-0c3eeda27c12@app.fastmail.com>
Date: Fri, 18 Oct 2024 16:01:17 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Dmitry Baryshkov" <dmitry.baryshkov@...aro.org>,
 "Arnd Bergmann" <arnd@...nel.org>
Cc: "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
 "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "Dave Airlie" <airlied@...il.com>,
 "Simona Vetter" <simona@...ll.ch>, "Philipp Zabel" <p.zabel@...gutronix.de>,
 "Jani Nikula" <jani.nikula@...el.com>,
 "Geert Uytterhoeven" <geert+renesas@...der.be>,
 "Imre Deak" <imre.deak@...el.com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge-connector: select DRM_DISPLAY_HELPER from
 DRM_BRIDGE_CONNECTOR

On Fri, Oct 18, 2024, at 15:42, Dmitry Baryshkov wrote:
> On Fri, Oct 18, 2024 at 03:08:45PM +0000, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@...db.de>
>> 
>> The imx display drivers use the new bridge connector helpers but don't
>> explicitly select CONFIG_DRM_DISPLAY_HELPER, leading to a link failure
>> in rare configurations:
>> 
>> ld.lld-20: error: undefined symbol: drm_bridge_connector_init
>> >>> referenced by imx-ldb.c
>> >>>               drivers/gpu/drm/imx/ipuv3/imx-ldb.o:(imx_ldb_bind) in archive vmlinux.a
>> >>> referenced by parallel-display.c
>> >>>               drivers/gpu/drm/imx/ipuv3/parallel-display.o:(imx_pd_bind) in archive vmlinux.a
>> 
>> Move DRM_BRIDGE_CONNECTOR out of the DRM_DISPLAY_HELPER block and
>> instead select that symbol indirectly.
>> 
>> Fixes: f94b9707a1c9 ("drm/imx: parallel-display: switch to imx_legacy_bridge / drm_bridge_connector")
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>
> I think a correct fix is to select DRM_DISPLAY_HELPER instead.

I think I just didn't express that clearly enough, selecting
DRM_DISPLAY_HELPER is what I did and what I tried to explain:

>>  config DRM_BRIDGE_CONNECTOR
>>  	bool
>>  	select DRM_DISPLAY_HDMI_STATE_HELPER
>> +	select DRM_DISPLAY_HELPER
>>  	help
>>  	  DRM connector implementation terminating DRM bridge chains.

I had to move the 'if' block just to avoid a circular
dependency.

Or did you mean the imx driver is the one that should
'select DRM_DISPLAY_HELPER'? That would also work, but
adds a bit more complexity.

      Arnd