On 10/27/21 14:55, Jani Nikula wrote:
[snip]
Why the dependency has to be in a user-visible symbol? What could be the problem with having something like:
diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index cea777ae7fb9..f80b404946ca 100644 --- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -82,6 +82,7 @@ config DRM_DEBUG_SELFTEST config DRM_KMS_HELPER tristate depends on DRM
depends on (DRM_FBDEV_EMULATION && FB) || !DRM_FBDEV_EMULATIONTo me, this seems like the right solution. Depend on FB if DRM_FBDEV_EMULATION is enabled. That's exactly what the relationship is.
The problem as Arnd explained is that then this relationship will have to be expressed in all the Kconfig symbols that select DRM_KMS_HELPER.
Otherwise the symbol will happily select the wrong state and even when a warning is printed by Kconfig, it will just set an invalid configuration.
For example with CONFIG_FB=m (that led to the linker errors if the symbol is also not CONFIG_DRM_KMS_HELPER=m) and CONFIG_SIMPLEDRM=y (that selects CONFIG_DRM_KMS_HELPER), this would cause the following unmet dependencies:
$ make prepare modules_prepare WARNING: unmet direct dependencies detected for DRM_KMS_HELPER Depends on [m]: HAS_IOMEM [=y] && DRM [=y] && (DRM_FBDEV_EMULATION [=y] && FB [=m] || !DRM_FBDEV_EMULATION [=y]) Selected by [y]: - DRM_SIMPLEDRM [=y] && HAS_IOMEM [=y] && DRM [=y] Selected by [m]: - DRM_I915 [=m] && HAS_IOMEM [=y] && DRM [=y] && X86 [=y] && PCI [=y] - DRM_VIRTIO_GPU [=m] && HAS_IOMEM [=y] && DRM [=y] && VIRTIO_MENU [=y] && MMU [=y]
so CONFIG_DRM_KMS_HELPER will wrongly set to =y which will cause the issue.
Best regards,