Re: [RFC PATCH] powerpc: Add check to select PPC_RADIX_BROADCAST_TLBIE

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

Christophe Leroy <christophe.leroy@csgroup.eu> writes:

> Le 07/04/2025 à 21:10, Ritesh Harjani (IBM) a écrit :
>> Madhavan Srinivasan <maddy@linux.ibm.com> writes:
>> 
>>> Commit 3d45a3d0d2e6 ("powerpc: Define config option for processors with broadcast TLBIE")
>> 
>> We may need to add above to Fixes tag as well, no?
>> 
>>> added a config option PPC_RADIX_BROADCAST_TLBIE to support processors with
>>> broadcast TLBIE. Since this option is relevant only for RADIX_MMU, add
>>> a check as a dependency to enable PPC_RADIX_BROADCAST_TLBIE in both
>>> powernv and pseries configs. This fixes the unmet config dependency
>>> warning reported
>>>
>>>     WARNING: unmet direct dependencies detected for PPC_RADIX_BROADCAST_TLBIE
>>>       Depends on [n]: PPC_RADIX_MMU [=n]
>>>       Selected by [y]:
>>>       - PPC_PSERIES [=y] && PPC64 [=y] && PPC_BOOK3S [=y]
>>>
>>> Reported-by: kernel test robot <lkp@intel.com>
>>> Closes: https://lore.kernel.org/oe-kbuild-all/202504051857.jRqxM60c-lkp@intel.com/
>>> Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
>> 
>> It's a bit strange that even though PPC_RADIX_BROADCAST_TLBIE adds
>> PPC_RADIX_MMU as a dependency where is it defined, we still have to add
>> an extra check for the same dependency to enable this for any platform.
>
> That's expected, see 

Yes. I had figured that out. 

> https://docs.kernel.org/kbuild/kconfig-language.html#menu-attributes :

Ok! Good to see we have this properly documented as well. Thanks for
pointing out the documentation link.

>
> 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.
>
> Christophe
>

Make sense. Thanks! for adding the details.

-ritesh