Re: [V14 3/8] drivers: perf: arm_pmuv3: Enable branch stack sampling framework

[James Clark]

On 15/11/2023 05:44, Anshuman Khandual wrote:
> On 11/14/23 15:28, James Clark wrote:
>>
>>
>> On 14/11/2023 05:13, Anshuman Khandual wrote:
>>> Branch stack sampling support i.e capturing branch records during execution
>>> in core perf, rides along with normal HW events being scheduled on the PMU.
>>> This prepares ARMV8 PMU framework for branch stack support on relevant PMUs
>>> with required HW implementation.
>>>
>>
>> [...]
>>
>>> - All armv8pmu_branch_xxxx() stub definitions have been moved inside
>>>   include/linux/perf/arm_pmuv3.h for easy access from both arm32 and
>>>   arm64 platforms
>>>
>>
>> This causes lots of W=1 build errors because the prototypes are in
>> arm_pmuv3.h, but arm_brbe.c doesn't include it.
> 
> I guess these are the W=1 warnings you mentioned above.
> 
> drivers/perf/arm_brbe.c:11:6: warning: no previous prototype for ‘armv8pmu_branch_reset’ [-Wmissing-prototypes]
>    11 | void armv8pmu_branch_reset(void)                                                                                                                                                                   
>       |      ^~~~~~~~~~~~~~~~~~~~~                                                                                                                                                                         
> drivers/perf/arm_brbe.c:190:6: warning: no previous prototype for ‘armv8pmu_branch_save’ [-Wmissing-prototypes]      
>   190 | void armv8pmu_branch_save(struct arm_pmu *arm_pmu, void *ctx)                      
>       |      ^~~~~~~~~~~~~~~~~~~~                                                                                                                                                                          
> drivers/perf/arm_brbe.c:236:6: warning: no previous prototype for ‘armv8pmu_branch_attr_valid’ [-Wmissing-prototypes]
>   236 | bool armv8pmu_branch_attr_valid(struct perf_event *event)                                                                                                                                          
>       |      ^~~~~~~~~~~~~~~~~~~~~~~~~~                                                                                                                                                                    
> drivers/perf/arm_brbe.c:269:5: warning: no previous prototype for ‘armv8pmu_task_ctx_cache_alloc’ [-Wmissing-prototypes]
>   269 | int armv8pmu_task_ctx_cache_alloc(struct arm_pmu *arm_pmu)                            
>       |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~                                                            
> drivers/perf/arm_brbe.c:279:6: warning: no previous prototype for ‘armv8pmu_task_ctx_cache_free’ [-Wmissing-prototypes]
>   279 | void armv8pmu_task_ctx_cache_free(struct arm_pmu *arm_pmu)                       
>       |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~                                                            
> drivers/perf/arm_brbe.c:303:6: warning: no previous prototype for ‘armv8pmu_branch_probe’ [-Wmissing-prototypes]
>   303 | void armv8pmu_branch_probe(struct arm_pmu *armpmu)                                
>       |      ^~~~~~~~~~~~~~~~~~~~~                                                                   
> drivers/perf/arm_brbe.c:449:6: warning: no previous prototype for ‘armv8pmu_branch_enable’ [-Wmissing-prototypes]
>   449 | void armv8pmu_branch_enable(struct arm_pmu *arm_pmu)                             
>       |      ^~~~~~~~~~~~~~~~~~~~~~                                                                  
> drivers/perf/arm_brbe.c:474:6: warning: no previous prototype for ‘armv8pmu_branch_disable’ [-Wmissing-prototypes]
>   474 | void armv8pmu_branch_disable(void)                                                           
>       |      ^~~~~~~~~~~~~~~~~~~~~~~                                                                 
> drivers/perf/arm_brbe.c:717:6: warning: no previous prototype for ‘armv8pmu_branch_read’ [-Wmissing-prototypes]
>   717 | void armv8pmu_branch_read(struct pmu_hw_events *cpuc, struct perf_event *event)
> 
> Branch helpers are used in ARM PMU V3 driver i.e drivers/perf/arm_pmuv3.c.
> Whether the actual BRBE helper definitions, or their fallback stubs (when
> CONFIG_ARM64_BRBE is not enabled), need to be accessible from arm_pmuv3.c
> driver not from brbe.c implementations itself.
> 
>>
>> It seems like the main reason you can't include arm_brbe.h in arm32 code
>> is because there are a load of inline functions and references to
>> registers in there. But these are only used in arm_brbe.c, so they don't
> 
> Right, arm32 should not be exposed to BRBE internals via arm_brbe.h header.
> 
>> need to be in the header anyway.
> 
> Right, these are only used in arm_brbe.c
> 
>>
>> If you removed the code from the header and moved it to the source file
>> you could move the brbe prototypes to the brbe header and it would be a
>> bit cleaner and more idiomatic.
> 
> Alight, how about the following changes - build tested on arm32 and arm64.
> 
> - Move BRBE helpers from arm_brbe.h into arm_brbe.c
> - Move armv8_pmu_xxx() declaration inside arm_brbe.h for arm64 (CONFIG_ARM64_BRBE)
> - Move armv8_pmu_xxx() stub definitions inside arm_pmuv3.c for arm32 (!CONFIG_ARM64_BRBE)
> - Include arm_brbe.h header both in arm_pmuv3.c and arm_brbe.c

Agree to them all except:

  - Move armv8_pmu_xxx() stub definitions inside arm_pmuv3.c for arm32
(!CONFIG_ARM64_BRBE)

Normally you put the stubs right next to the prototypes with #else, so
in this case both would be in arm_brbe.h. Not sure what the reason for
splitting them here is? You already said "include arm_brbe.h in
arm_pmuv3.c", so that covers arm32 too.