Re: [PATCH] drm/bridge: Select DRM_KMS_HELPER for DRM_PANEL_BRIDGE

From: Neil Armstrong <neil.armstrong@linaro.org>
To: Luca Weiss <luca.weiss@fairphone.com>,
	Andrzej Hajda <andrzej.hajda@intel.com>,
	Robert Foss <rfoss@kernel.org>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>
Cc: ~postmarketos/upstreaming@lists.sr.ht,
	phone-devel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/bridge: Select DRM_KMS_HELPER for DRM_PANEL_BRIDGE
Date: Mon, 15 Jan 2024 09:43:32 +0100	[thread overview]
Message-ID: <b1da07f9-7e15-4d83-bef3-d0ce157654bc@linaro.org> (raw)
In-Reply-To: <20240111-drm-panel-bridge-fixup-v1-1-e06292f6f500@fairphone.com>

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@fairphone.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,