linux-kernel - [PATCH AUTOSEL 6.14 002/102] drm/bridge: select DRM_KMS_HELPER for AUX

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Message-Id: <20250601232937.3510379-2-sashal@kernel.org>
Date: Sun,  1 Jun 2025 19:27:54 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
	stable@...r.kernel.org
Cc: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Sasha Levin <sashal@...nel.org>,
	andrzej.hajda@...el.com,
	rfoss@...nel.org,
	maarten.lankhorst@...ux.intel.com,
	mripard@...nel.org,
	tzimmermann@...e.de,
	airlied@...il.com,
	simona@...ll.ch,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 6.14 002/102] drm/bridge: select DRM_KMS_HELPER for AUX_BRIDGE

From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>

[ Upstream commit b12fa5e76e1463fc5a196f2717040e4564e184b6 ]

The aux bridge uses devm_drm_of_get_bridge() from the panel bridge (and
correctly selects DRM_PANEL_BRIDGE). However panel bridge is not a
separate module, it is compiled into the drm_kms_helper.o. Select
DRM_KMS_HELPER too to express this dependency.

Reviewed-by: Neil Armstrong <neil.armstrong@...aro.org>
Link: https://lore.kernel.org/r/20250411-aux-select-kms-v1-1-c4276f905a56@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---

Based on my analysis, here is my determination: **YES** This commit
should be backported to stable kernel trees for the following reasons:
1. **It fixes a missing dependency issue**: The commit addresses a real
dependency problem where `DRM_AUX_BRIDGE` uses
`devm_drm_of_get_bridge()` which is implemented in `bridge/panel.c`. As
shown in the Makefile analysis, `panel.o` is built into
`drm_kms_helper.o` when `CONFIG_DRM_PANEL_BRIDGE` is selected (line 149
of drivers/gpu/drm/Makefile: `drm_kms_helper-$(CONFIG_DRM_PANEL_BRIDGE)
+= bridge/panel.o`). 2. **It prevents build failures**: Without
selecting `DRM_KMS_HELPER`, the aux bridge can fail to link properly
because the actual implementation of `devm_drm_of_get_bridge()` won't be
available. This can lead to undefined reference errors during linking,
similar to the issue described in Similar Commit #1 where
`devm_drm_of_get_bridge` was undefined. 3. **The fix is minimal and
safe**: The change is a simple one-line addition to select
`DRM_KMS_HELPER` in the Kconfig. This is a build configuration fix with
no runtime impact - it merely ensures the correct dependencies are
satisfied at build time. 4. **It follows established patterns**: Looking
at other bridge drivers in the same Kconfig file, we can see that
drivers using similar functionality already select `DRM_KMS_HELPER`
(e.g., lines 38, 53, 64, 88, 99 in the Kconfig show other drivers
selecting it). 5. **Similar to backported commit #2**: This fix is
conceptually similar to Similar Commit #2 which was backported and dealt
with circular dependencies and proper module organization for
`devm_drm_of_get_bridge()`. 6. **No architectural changes**: This commit
doesn't introduce new features or change any architecture - it simply
fixes a missing Kconfig dependency that should have been there from the
beginning when `DRM_AUX_BRIDGE` was introduced. The commit meets the
stable tree criteria as it: - Fixes a real bug (missing dependency
leading to potential build failures) - Is minimal and contained (single
line Kconfig change) - Has no risk of regression (only affects build
configuration) - Doesn't introduce new features or architectural changes

 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 6b4664d91faa8..631b8db08ecf7 100644
--- a/drivers/gpu/drm/bridge/Kconfig
+++ b/drivers/gpu/drm/bridge/Kconfig
@@ -16,6 +16,7 @@ config DRM_AUX_BRIDGE
 	tristate
 	depends on DRM_BRIDGE && OF
 	select AUXILIARY_BUS
+	select DRM_KMS_HELPER
 	select DRM_PANEL_BRIDGE
 	help
 	  Simple transparent bridge that is used by several non-DRM drivers to
-- 
2.39.5