From: Dmitry Baryshkov dmitry.baryshkov@oss.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@linaro.org Link: https://lore.kernel.org/r/20250411-aux-select-kms-v1-1-c4276f905a56@oss.qual... Signed-off-by: Dmitry Baryshkov dmitry.baryshkov@oss.qualcomm.com Signed-off-by: Sasha Levin sashal@kernel.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 3eb955333c809..0385dd8e16283 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