arm_pmu: factor out PMU matching

A subsequent patch will rework the ACPI probing of PMUs, and we'll need
to match a CPU with a known cpuid in two separate paths.

Factor out the matching logic into a helper function so that it can be
reused.

There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Pierre Gondois <pierre.gondois@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-and-tested-by: Pierre Gondois <pierre.gondois@arm.com>
Link: https://lore.kernel.org/r/20220930111844.1522365-3-mark.rutland@arm.comSigned-off-by: Will Deacon <will@kernel.org>

drivers/perf/arm_pmu_acpi.c

@@ -187,7 +187,7 @@ static int arm_pmu_acpi_parse_irqs(void)
 	return err;
 }
 
-static struct arm_pmu *arm_pmu_acpi_find_alloc_pmu(void)
+static struct arm_pmu *arm_pmu_acpi_find_pmu(void)
 {
 	unsigned long cpuid = read_cpuid_id();
 	struct arm_pmu *pmu;
@@ -201,6 +201,17 @@ static struct arm_pmu *arm_pmu_acpi_find_alloc_pmu(void)
 		return pmu;
 	}
 
+	return NULL;
+}
+
+static struct arm_pmu *arm_pmu_acpi_find_alloc_pmu(void)
+{
+	struct arm_pmu *pmu;
+
+	pmu = arm_pmu_acpi_find_pmu();
+	if (pmu)
+		return pmu;
+
 	pmu = armpmu_alloc_atomic();
 	if (!pmu) {
 		pr_warn("Unable to allocate PMU for CPU%d\n",
@@ -208,7 +219,7 @@ static struct arm_pmu *arm_pmu_acpi_find_alloc_pmu(void)
 		return NULL;
 	}
 
-	pmu->acpi_cpuid = cpuid;
+	pmu->acpi_cpuid = read_cpuid_id();
 
 	return pmu;
 }