linux-kernel - Re: [PATCH] drm/bridge: Select DRM_KMS_HELPER for DRM_PANEL

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Date: Mon, 15 Jan 2024 09:43:32 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Luca Weiss <luca.weiss@...rphone.com>,
 Andrzej Hajda <andrzej.hajda@...el.com>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>
Cc: ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: Select DRM_KMS_HELPER for DRM_PANEL_BRIDGE

Hi Luca,

On 11/01/2024 13:38, Luca Weiss wrote:
> Since the kconfig symbol of DRM_PANEL_BRIDGE is only adding
> bridge/panel.o to drm_kms_helper object, we need to select
> DRM_KMS_HELPER to make sure the file is actually getting built.
> 
> Otherwise with certain defconfigs e.g. devm_drm_of_get_bridge will not
> be properly available:
> 
>    aarch64-linux-gnu-ld: drivers/phy/qualcomm/phy-qcom-qmp-combo.o: in function `qmp_combo_bridge_attach':
>    drivers/phy/qualcomm/phy-qcom-qmp-combo.c:3204:(.text+0x8f4): undefined reference to `devm_drm_of_get_bridge'
> 
> Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
> ---
> I can see "depends on DRM_KMS_HELPER" was removed with commit
> 3c3384050d68 ("drm: Don't make DRM_PANEL_BRIDGE dependent on DRM_KMS_HELPERS")
> 
> I'm not too familiar with Kconfig but it feels more correct if
> PHY_QCOM_QMP_COMBO selects DRM_PANEL_BRIDGE that that's enough; and it
> doesn't also has to explicitly select DRM_KMS_HELPER because of how the
> objects are built in the Makefile.
> 
> Alternatively solution to this patch could be adjusting this line in
> include/drm/drm_bridge.h:
> 
>    -#if defined(CONFIG_OF) && defined(CONFIG_DRM_PANEL_BRIDGE)
>    +#if defined(CONFIG_OF) && defined(CONFIG_DRM_PANEL_BRIDGE) && defined(CONFIG_DRM_KMS_HELPER)
>     struct drm_bridge *devm_drm_of_get_bridge(struct device *dev, struct device_node *node,
>                                              u32 port, u32 endpoint);
> 
> .. and then selecting DRM_KMS_HELPER for PHY_QCOM_QMP_COMBO.
> 
> But I think the solution in this patch is better. Let me know what you
> think.

I think this is no more the case after on linux-next:
35921910bbd0 phy: qcom: qmp-combo: switch to DRM_AUX_BRIDGE

But could you still check ?

Neil

> ---
>   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 ac9ec5073619..ae782b427829 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -8,6 +8,7 @@ config DRM_BRIDGE
>   config DRM_PANEL_BRIDGE
>   	def_bool y
>   	depends on DRM_BRIDGE
> +	select DRM_KMS_HELPER
>   	select DRM_PANEL
>   	help
>   	  DRM bridge wrapper of DRM panels
> 
> ---
> base-commit: b9c3a1fa6fb324e691a03cf124b79f4842e65d76
> change-id: 20240111-drm-panel-bridge-fixup-5c2977fb969f
> 
> Best regards,