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: 1b600da51073 ("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>

diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
index d9b7e2b..4160624 100644 (file)
--- a/kernel/power/energy_model.c
+++ b/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;