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

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Message-Id: <20240111-drm-panel-bridge-fixup-v1-1-e06292f6f500@fairphone.com>
Date: Thu, 11 Jan 2024 13:38:04 +0100
From: Luca Weiss <luca.weiss@...rphone.com>
To: Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, 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, 
 Luca Weiss <luca.weiss@...rphone.com>
Subject: [PATCH] drm/bridge: Select DRM_KMS_HELPER for DRM_PANEL_BRIDGE

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.
---
 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,
-- 
Luca Weiss <luca.weiss@...rphone.com>