PM: EM: Expose the ID of a performance domain via debugfs

For ease of debugging, let's expose the assigned ID of a performance
domain through debugfs (e.g., /sys/kernel/debug/energy_model/cpu0/id).

Signed-off-by: Changwoo Min <changwoo@igalia.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/20251020220914.320832-3-changwoo@igalia.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: multics69

kernel/power/energy_model.c

@@ -126,6 +126,16 @@ static int em_debug_flags_show(struct seq_file *s, void *unused)
 }
 DEFINE_SHOW_ATTRIBUTE(em_debug_flags);
 
+static int em_debug_id_show(struct seq_file *s, void *unused)
+{
+	struct em_perf_domain *pd = s->private;
+
+	seq_printf(s, "%d\n", pd->id);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(em_debug_id);
+
 static void em_debug_create_pd(struct device *dev)
 {
 	struct em_dbg_info *em_dbg;
@@ -142,6 +152,8 @@ static void em_debug_create_pd(struct device *dev)
 	debugfs_create_file("flags", 0444, d, dev->em_pd,
 			    &em_debug_flags_fops);
 
+	debugfs_create_file("id", 0444, d, dev->em_pd, &em_debug_id_fops);
+
 	em_dbg = devm_kcalloc(dev, dev->em_pd->nr_perf_states,
 			      sizeof(*em_dbg), GFP_KERNEL);
 	if (!em_dbg)