Re: [PATCH 04/11] drm/panel: merge the drm_kms_helper module into the drm module

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Low] The use of `:=` instead of `+=` for `drm-$(CONFIG_DRM_KMS_HELPER)` overwrites the previously defined `drm-y` list, causing all core DRM objects to be excluded from the build.
- [Low] Merging `drm_kms_helper` into the `drm` module breaks the build or module loading when `CONFIG_DRM=y` and `CONFIG_DRM_KMS_HELPER=m` because Kbuild ignores `drm-m` for built-in objects.
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--- Patch [4]: [PATCH 04/11] drm/panel: merge the drm_kms_helper module into the drm module ---
commit d831428a6450fb748ee21e10b4e68b33d57ee2c3
Author: Luca Ceresoli <[email protected]>

drm/panel: merge the drm_kms_helper module into the drm module

Work is in progress to make every drm_panel automatically create a panel_bridge,
which requires calling drm_panel_bridge APIs. This would create a circular
dependency loop on modular builds. This commit attempts to move the entire
drm_kms_helper into the drm module to resolve the dependency loop.

Link: https://lore.kernel.org/all/emuj2innmp6zmzd7pyakqzjqpdzhly6qfhakya3ydwmd63pl26@5jwxaidpikjw/
Link: https://lore.kernel.org/lkml/[email protected]/

> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -139,7 +139,7 @@ obj-$(CONFIG_DRM_TTM_HELPER) += drm_ttm_helper.o
>  # Modesetting helpers
>  #
>  
> -drm_kms_helper-y := \
> +drm-$(CONFIG_DRM_KMS_HELPER) := \

[Severity: Low]
Does this `:=` assignment overwrite the core DRM objects defined earlier in
the Makefile? If `CONFIG_DRM_KMS_HELPER=y`, this evaluates to `drm-y :=`,
replacing the previously built list for `drm-y`. This would cause the core
DRM files to be dropped from the build.

[Severity: Low]
What happens to the build if `CONFIG_DRM=y` and `CONFIG_DRM_KMS_HELPER=m`?

In this configuration, the objects are appended to `drm-m`. Since the
parent object is built-in (`obj-y += drm.o`), Kbuild ignores the `drm-m`
list entirely. Could this cause the KMS helpers to be silently omitted
from compilation, leading to unresolved symbols in modular drivers that
depend on them?

>  	drm_atomic_helper.o \
>  	drm_atomic_state_helper.o \

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Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=4