Re: [Intel-gfx] [PATCH 1/7] drm/i915/hwmon: Add HWMON infrastructure

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 23 Aug 2022, "Nilawar, Badal" <badal.nilawar@intel.com> wrote:
> On 23-08-2022 19:05, Jani Nikula wrote:
>> On Tue, 23 Aug 2022, Guenter Roeck <linux@roeck-us.net> wrote:
>>> On Tue, Aug 23, 2022 at 12:46:14PM +0300, Jani Nikula wrote:
>>> [ ... ]
>>>>>>
>>>>>> So why not do this in i915 Kconfig:
>>>>>>
>>>>>> config DRM_I915
>>>>>> 	...
>>>>>> 	depends on HWMON || HWMON=n
>>>>> With this change I am getting recursive dependancy error when I run make
>>>>> oldconfig
>>>>>
>>>>> badal@bnilawar-desk1:~/workspace/wp3/drm-tip$ make oldconfig
>>>>>     HOSTCC  scripts/basic/fixdep
>>>>>     HOSTCC  scripts/kconfig/conf.o
>>>>>     HOSTCC  scripts/kconfig/confdata.o
>>>>>     HOSTCC  scripts/kconfig/expr.o
>>>>>     LEX     scripts/kconfig/lexer.lex.c
>>>>>     YACC    scripts/kconfig/parser.tab.[ch]
>>>>>     HOSTCC  scripts/kconfig/lexer.lex.o
>>>>>     HOSTCC  scripts/kconfig/menu.o
>>>>>     HOSTCC  scripts/kconfig/parser.tab.o
>>>>>     HOSTCC  scripts/kconfig/preprocess.o
>>>>>     HOSTCC  scripts/kconfig/symbol.o
>>>>>     HOSTCC  scripts/kconfig/util.o
>>>>>     HOSTLD  scripts/kconfig/conf
>>>>> drivers/gpu/drm/i915/Kconfig:2:error: recursive dependency detected!
>>>>> drivers/gpu/drm/i915/Kconfig:2: symbol DRM_I915 depends on HWMON
>>>>> drivers/hwmon/Kconfig:6:        symbol HWMON is selected by EEEPC_LAPTOP
>>>>> drivers/platform/x86/Kconfig:332:       symbol EEEPC_LAPTOP depends on INPUT
>>>>> drivers/input/Kconfig:8:        symbol INPUT is selected by DRM_I915
>>>>> For a resolution refer to Documentation/kbuild/kconfig-language.rst
>>>>> subsection "Kconfig recursive dependency limitations"
>>>>
>>>> *sigh*
>>>>
>>>>    Note:
>>>> 	select should be used with care. select will force
>>>> 	a symbol to a value without visiting the dependencies.
>>>> 	By abusing select you are able to select a symbol FOO even
>>>> 	if FOO depends on BAR that is not set.
>>>> 	In general use select only for non-visible symbols
>>>> 	(no prompts anywhere) and for symbols with no dependencies.
>>>> 	That will limit the usefulness but on the other hand avoid
>>>> 	the illegal configurations all over.
>>>>
>>> Agreed. HWMON should not be selected anywhere. Unfortunately it is, and
>>> drm is no exception. It is selected by DRM_RADEON and DRM_AMDGPU.
>>> Maybe just select it in DRM_I915 as well after all; in practice it won't
>>> make a difference.
>> 
>> And I guess everyone just does what I'm about to do now, throw my hands
>> up in the air in disgust and resignation. :p
> How about sticking to existing approach only. In my previous response I 
> mentioned that for combo which we want to reject CONFIG_HWMON=m && 
> CONFIG_DRM_I915=y combo i915_hwmon.o is not getting build.
> It is only getting build for below combos
> CONFIG_HWMON=m && CONFIG_DRM_I915=y
> CONFIG_HWMON=m && CONFIG_DRM_I915=m
> CONFIG_HWMON=y && CONFIG_DRM_I915=m

Then please hide the IS_REACHABLE() within i915_hwmon.h and add stubs as
is customary. Let's not clutter high level driver code with some random
#if directives.

BR,
Jani.


> Regards,
> Badal
>> 
>> BR,
>> Jani.
>> 
>> 
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center