powercap: intel_rapl: Expose all package CPUs in PMU cpumask

Currently, the RAPL PMU cpumask only includes one CPU per package
(typically the lead_cpu) for both MSR and TPMI interfaces. This
forces tools to pin their operations to that specific CPU, even
though package-scoped registers are readable from any CPU within
the package.

Change the cpumask to include all online CPUs in each package. This
allows tools like perf and turbostat to read RAPL events from any
CPU in the package without requiring special handling to find and
use the designated lead_cpu.

The change refactors get_pmu_cpu() into set_pmu_cpumask() which
populates the cpumask with all CPUs belonging to each RAPL package
instead of returning a single CPU.

This improves flexibility for userspace tools while maintaining
correctness since package-scoped RAPL MSRs are architecturally
accessible from any CPU in the package.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Tested-by: Furquim Ulisses <ulisses.furquim@intel.com>
Reviewed-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20260209234310.1440722-3-sathyanarayanan.kuppuswamy@linux.intel.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: Kuppuswamy Sathyanarayanan

drivers/powercap/intel_rapl_common.c

@@ -1590,23 +1590,21 @@ static struct rapl_pmu rapl_pmu;
 
 /* PMU helpers */
 
-static int get_pmu_cpu(struct rapl_package *rp)
+static void set_pmu_cpumask(struct rapl_package *rp, cpumask_var_t mask)
 {
 	int cpu;
 
 	if (!rp->has_pmu)
-		return nr_cpu_ids;
+		return;
 
 	/* Only TPMI & MSR RAPL are supported for now */
 	if (rp->priv->type != RAPL_IF_TPMI && rp->priv->type != RAPL_IF_MSR)
-		return nr_cpu_ids;
+		return;
 
 	/* TPMI/MSR RAPL uses any CPU in the package for PMU */
 	for_each_online_cpu(cpu)
 		if (topology_physical_package_id(cpu) == rp->id)
-			return cpu;
-
-	return nr_cpu_ids;
+			cpumask_set_cpu(cpu, mask);
 }
 
 static bool is_rp_pmu_cpu(struct rapl_package *rp, int cpu)
@@ -1883,7 +1881,6 @@ static ssize_t cpumask_show(struct device *dev,
 {
 	struct rapl_package *rp;
 	cpumask_var_t cpu_mask;
-	int cpu;
 	int ret;
 
 	if (!alloc_cpumask_var(&cpu_mask, GFP_KERNEL))
@@ -1895,9 +1892,7 @@ static ssize_t cpumask_show(struct device *dev,
 
 	/* Choose a cpu for each RAPL Package */
 	list_for_each_entry(rp, &rapl_packages, plist) {
-		cpu = get_pmu_cpu(rp);
-		if (cpu < nr_cpu_ids)
-			cpumask_set_cpu(cpu, cpu_mask);
+		set_pmu_cpumask(rp, cpu_mask);
 	}
 	cpus_read_unlock();