[PATCH -next] perf: arm_pmu: Fix build on arm if !CONFIG_GENERIC_ARCH_TOPOLOGY

[Yicong Yang]

On 2025/11/5 00:33, Will Deacon wrote:
> On Tue, Nov 04, 2025 at 09:40:04PM +0800, Yicong Yang wrote:
>> The SMT implementation is retrieved by topology_core_has_smt() which
>> depends on CONFIG_GENERIC_ARCH_TOPOLOGY. The config is optional on
>> arm platforms so protect the usage with CONFIG_GENERIC_ARCH_TOPOLOGY.
>>
>> Fixes: c3d78c34ad00 ("perf: arm_pmuv3: Don't use PMCCNTR_EL0 on SMT cores")
>> Reported-by: kernel test robot <lkp at intel.com>
>> Closes: https://lore.kernel.org/oe-kbuild-all/202511041757.vuCGOmFc-lkp@intel.com/
>> Signed-off-by: Yicong Yang <yangyccccc at gmail.com>
>> ---
>>  drivers/perf/arm_pmu.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
>> index ae437791b5f8..f38bdeb906f0 100644
>> --- a/drivers/perf/arm_pmu.c
>> +++ b/drivers/perf/arm_pmu.c
>> @@ -925,11 +925,13 @@ int armpmu_register(struct arm_pmu *pmu)
>>  	if (ret)
>>  		return ret;
>>  
>> +#ifdef CONFIG_GENERIC_ARCH_TOPOLOGY
>>  	/*
>>  	 * By this stage we know our supported CPUs on either DT/ACPI platforms,
>>  	 * detect the SMT implementation.
>>  	 */
>>  	pmu->has_smt = topology_core_has_smt(cpumask_first(&pmu->supported_cpus));
>> +#endif
>>  
>>  	if (!pmu->set_event_filter)
>>  		pmu->pmu.capabilities |= PERF_PMU_CAP_NO_EXCLUDE;
>> -- 
>> 2.50.1 (Apple Git-155)
> Wouldn't we be better off adding something like:
>
> #else
> static inline bool topology_core_has_smt(int cpu) { return false; }
> #endif /* CONFIG_GENERIC_ARCH_TOPOLOGY */
>
> to the bottom of include/linux/arch_topology.h?

I was thinking so but found there's no !CONFIG_GENERIC_ARCH_TOPOLOGY
stubs for other functions. So I checked how this is handled in other places and follow in
the same way [1]

but a stub will be neater here. will respin a version using the stub.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/kernel/smp.c?h=v6.18-rc4#n261

thanks.