Subject: Re: [PATCH 2/2] powerpc/papr_scm: Fix build failure when CONFIG_PERF_EVENTS is not set

From: Vaibhav Jain <[email-masked]>
Date: Wed, 23 Mar 2022 13:18:33 +0530

Dan Williams <[email-masked]> writes:

> On Tue, Mar 22, 2022 at 7:30 AM kajoljain <[email-masked]> wrote:
>>
>>
>>
>> On 3/22/22 03:09, Dan Williams wrote:
>> > On Fri, Mar 18, 2022 at 4:42 AM Kajol Jain <[email-masked]> wrote:
>> >>
>> >> The following build failure occures when CONFIG_PERF_EVENTS is not set
>> >> as generic pmu functions are not visible in that scenario.
>> >>
>> >> arch/powerpc/platforms/pseries/papr_scm.c:372:35: error: ‘struct perf_event’ has no member named ‘attr’
>> >>          p->nvdimm_events_map[event->attr.config],
>> >>                                    ^~
>> >> In file included from ./include/linux/list.h:5,
>> >>                  from ./include/linux/kobject.h:19,
>> >>                  from ./include/linux/of.h:17,
>> >>                  from arch/powerpc/platforms/pseries/papr_scm.c:5:
>> >> arch/powerpc/platforms/pseries/papr_scm.c: In function ‘papr_scm_pmu_event_init’:
>> >> arch/powerpc/platforms/pseries/papr_scm.c:389:49: error: ‘struct perf_event’ has no member named ‘pmu’
>> >>   struct nvdimm_pmu *nd_pmu = to_nvdimm_pmu(event->pmu);
>> >>                                                  ^~
>> >> ./include/linux/container_of.h:18:26: note: in definition of macro ‘container_of’
>> >>   void *__mptr = (void *)(ptr);     \
>> >>                           ^~~
>> >> arch/powerpc/platforms/pseries/papr_scm.c:389:30: note: in expansion of macro ‘to_nvdimm_pmu’
>> >>   struct nvdimm_pmu *nd_pmu = to_nvdimm_pmu(event->pmu);
>> >>                               ^~~~~~~~~~~~~
>> >> In file included from ./include/linux/bits.h:22,
>> >>                  from ./include/linux/bitops.h:6,
>> >>                  from ./include/linux/of.h:15,
>> >>                  from arch/powerpc/platforms/pseries/papr_scm.c:5:
>> >>
>> >> Fix the build issue by adding check for CONFIG_PERF_EVENTS config option
>> >> and disabling the papr_scm perf interface support incase this config
>> >> is not set
>> >>
>> >> Fixes: 4c08d4bbc089 ("powerpc/papr_scm: Add perf interface support") (Commit id
>> >> based on linux-next tree)
>> >> Signed-off-by: Kajol Jain <[email-masked]>
>> >> ---
>> >>  arch/powerpc/platforms/pseries/papr_scm.c | 15 +++++++++++++++
>> >
>> > This is a bit messier than I would have liked mainly because it dumps
>> > a bunch of ifdefery into a C file contrary to coding style, "Wherever
>> > possible, don't use preprocessor conditionals (#if, #ifdef) in .c
>> > files". I would expect this all to move to an organization like:
>>
>> Hi Dan,
>>       Thanks for reviewing the patches. Inorder to avoid the multiple
>> ifdefs checks, we can also add stub function for papr_scm_pmu_register.
>> With that change we will just have one ifdef check for
>> CONFIG_PERF_EVENTS config in both papr_scm.c and nd.h file. Hence we can
>> avoid adding new files specific for papr_scm perf interface.
>>
>> Below is the code snippet for that change, let me know if looks fine to
>> you. I tested it
>> with set/unset PAPR_SCM config value and set/unset PERF_EVENTS config
>> value combinations.
>>
>> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c
>> b/arch/powerpc/platforms/pseries/papr_scm.c
>> index 4dd513d7c029..38fabb44d3c3 100644
>> --- a/arch/powerpc/platforms/pseries/papr_scm.c
>> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
>> @@ -69,8 +69,6 @@
>>  #define PAPR_SCM_PERF_STATS_EYECATCHER __stringify(SCMSTATS)
>>  #define PAPR_SCM_PERF_STATS_VERSION 0x1
>>
>> -#define to_nvdimm_pmu(_pmu)    container_of(_pmu, struct nvdimm_pmu, pmu)
>> -
>>  /* Struct holding a single performance metric */
>>  struct papr_scm_perf_stat {
>>         u8 stat_id[8];
>> @@ -346,6 +344,9 @@ static ssize_t drc_pmem_query_stats(struct
>> papr_scm_priv *p,
>>         return 0;
>>  }
>>
>> +#ifdef CONFIG_PERF_EVENTS
>> +#define to_nvdimm_pmu(_pmu)    container_of(_pmu, struct nvdimm_pmu, pmu)
>> +
>>  static int papr_scm_pmu_get_value(struct perf_event *event, struct
>> device *dev, u64 *count)
>>  {
>>         struct papr_scm_perf_stat *stat;
>> @@ -558,6 +559,10 @@ static void papr_scm_pmu_register(struct
>> papr_scm_priv *p)
>>         dev_info(&p->pdev->dev, "nvdimm pmu didn't register rc=%d\n", rc);
>>  }
>>
>> +#else
>> +static inline void papr_scm_pmu_register(struct papr_scm_priv *p) { }
>
> Since this isn't in a header file, it does not need to be marked
> "inline" the compiler will figure it out.
>
>> +#endif
>
> It might be time to create:
>
> arch/powerpc/platforms/pseries/papr_scm.h
>
> ...there is quite a bit of header material accrued in papr_scm.c and
> once the ifdefs start landing in it then it becomes a nominal coding
> style issue. That said, this is certainly more palatable than the
> previous version. So if you don't want to create papr_scm.h yet for
> this, at least make a note in the changelog that the first portion of
> arch/powerpc/platforms/pseries/papr_scm.c is effectively papr_scm.h
> content and may move there in the future, or something like that.

Great suggestion Dan and incidently we are already working on a patchset
to reconcile this by moving a bunch of these defines from papr_scm.c to a
header. That work is primarily done to towards remove the redundancy
between papr_scm and generic ndtest module that we have today. We will
post the patches in next few days.

-- 
Cheers
~ Vaibhav