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

[Dan Williams <dan.j.williams@intel.com>]

On Tue, Mar 22, 2022 at 7:30 AM kajoljain <kjain@linux.ibm.com> wrote:
>
>
>
> On 3/22/22 03:09, Dan Williams wrote:
> > On Fri, Mar 18, 2022 at 4:42 AM Kajol Jain <kjain@linux.ibm.com> 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 <kjain@linux.ibm.com>
> >> ---
> >>  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.