simpledrm problem: Kconfig:error: recursive dependency detected!

[David Herrmann]

Hey

On Thu, Aug 4, 2016 at 9:04 AM, Jani Nikula <jani.nikula at linux.intel.com> wrote:
> On Wed, 03 Aug 2016, Noralf Trønnes <noralf at tronnes.org> wrote:
>> Hi,
>>
>> I have changed simpledrm to use drm_simple_kms_helper and now I'm
>> facing this:
>>
>> drivers/video/fbdev/Kconfig:5:error: recursive dependency detected!
>> For a resolution refer to Documentation/kbuild/kconfig-language.txt
>>
>> drivers/video/fbdev/Kconfig:5:  symbol FB is selected by DRM_KMS_FB_HELPER
>>
>> drivers/gpu/drm/Kconfig:42:     symbol DRM_KMS_FB_HELPER depends on
>> DRM_KMS_HELPER
>>
>> drivers/gpu/drm/Kconfig:36:     symbol DRM_KMS_HELPER is selected by
>> DRM_SIMPLEDRM
>>
>> drivers/gpu/drm/simpledrm/Kconfig:1:    symbol DRM_SIMPLEDRM depends on
>> FB_SIMPLE
>>
>> drivers/video/fbdev/Kconfig:2428:       symbol FB_SIMPLE depends on FB
>>
>>
>> Using this Kconfig:
>>
>> config DRM_SIMPLEDRM
>>      tristate "Simple firmware framebuffer DRM driver"
>>      depends on DRM && (FB_SIMPLE = n)
>>      select DRM_KMS_HELPER
>>
>>
>> Is there a solution to this apart from depending on DRM_KMS_HELPER or
>> removing the FB_SIMPLE dependency?
>
> I think the underlying problem is the overuse of "select" all around. I
> think people use it for convenience because unsatisfied "depends" hides
> a menu option in menuconfig while "select" does not, and it's sometimes
> hard to find all the dependencies of an option just to *show* it in
> menuconfig.
>
> I don't know what the exact cause here is, but having hunted these down
> before, it's often a rabbit hole where you end up having to change a ton
> of config options to make it robust, and those changes get rejected
> because the menuconfig convenience is lost, and I've given up. :/
>
> Would be great to have a menuconfig feature to recursively enable and
> option and all dependencies. Perhaps we could then be more strict about
> using "select" for stuff with dependencies.

As a workaround, just drop the FB_SIMPLE dependency. It was really
just meant as a safety net in my original code. Nothing bad happens if
both are enabled. The first to be loaded wins, the other one will very
likely print a confusing error message and exit.

Thanks
David