linux-kernel - Re: [PATCH 7/8] drm/bridge: fix dependency for lvds-encoder

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Date:   Mon, 28 May 2018 11:02:53 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        David Airlie <airlied@...ux.ie>, Eric Anholt <eric@...olt.net>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Maciej Purski <m.purski@...sung.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] drm/bridge: fix dependency for lvds-encoder

Hi Arnd,

Thank you for the patch.

On Friday, 25 May 2018 18:50:14 EEST Arnd Bergmann wrote:
> The DRM panel bridge code is built into the kms helpers module, so we
> get a link error when trying to use it from a built-in driver while the
> kms helper is a loadable module:
> 
> drivers/gpu/drm/bridge/lvds-encoder.o: In function `lvds_encoder_probe':
> lvds-encoder.c:(.text+0x124): undefined reference to
> `devm_drm_panel_bridge_add'
> 
> This adds a the same dependency in the lvds-encoder that we use for all
> the other users of the panel bridge. I did not bisect the problem, but
> from inspection it seems to date back to the patch that separated out
> the panel bridge from lvds encoder.
> 
> Fixes: 13dfc0540a57 ("drm/bridge: Refactor out the panel wrapper from the
> lvds-encoder bridge.") Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/gpu/drm/bridge/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index 6caa47834194..cf47bfa7a050 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -46,6 +46,7 @@ config DRM_DUMB_VGA_DAC
>  config DRM_LVDS_ENCODER
>  	tristate "Transparent parallel to LVDS encoder support"
>  	depends on OF
> +	select DRM_KMS_HELPER
>  	select DRM_PANEL_BRIDGE
>  	help
>  	  Support for transparent parallel to LVDS encoders that don't require

Wouldn't it be better to apply the following ?

config DRM_PANEL_BRIDGE
	def_bool y
	depends on DRM_BRIDGE
-	depends on DRM_KMS_HELPER
+	select DRM_KMS_HELPER
	select DRM_PANEL
	help
	   DRM bridge wrapper of DRM panels

Otherwise you'll potentially have to patch every user of DRM_PANEL_BRIDGE as 
done in this patch.

-- 
Regards,

Laurent Pinchart