simpledrm problem: Kconfig:error: recursive dependency detected!

[Jani Nikula]

On Thu, 04 Aug 2016, David Herrmann <dh.herrmann at gmail.com> wrote:
> 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, and sorry about derailing into a non-helpful rant about
kconfig. :/

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Technology Center