PM: EM: Fix potential division-by-zero error in em_compute_costs()

JIRA: https://issues.redhat.com/browse/RHEL-110833

commit 179c0c7
Author: Yaxiong Tian <tianyaxiong@kylinos.cn>
Date:   Fri Apr 18 09:06:13 2025 +0800

    PM: EM: Fix potential division-by-zero error in em_compute_costs()

    When the device is of a non-CPU type, table[i].performance won't be
    initialized in the previous em_init_performance(), resulting in division
    by zero when calculating costs in em_compute_costs().

    Since the 'cost' algorithm is only used for EAS energy efficiency
    calculations and is currently not utilized by other device drivers, we
    should add the _is_cpu_device(dev) check to prevent this division-by-zero
    issue.

    Fixes: 1b600da ("PM: EM: Optimize em_cpu_energy() and remove division")
    Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
    Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
    Link: https://patch.msgid.link/tencent_7F99ED4767C1AF7889D0D8AD50F34859CE06@qq.com
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Signed-off-by: Steve Best <sbest@redhat.com>

Author: sfbest

kernel/power/energy_model.c

@@ -233,6 +233,10 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
 	unsigned long prev_cost = ULONG_MAX;
 	int i, ret;
 
+	/* This is needed only for CPUs and EAS skip other devices */
+	if (!_is_cpu_device(dev))
+		return 0;
+
 	/* Compute the cost of each performance state. */
 	for (i = nr_states - 1; i >= 0; i--) {
 		unsigned long power_res, cost;