Re: [PATCH v4] PM: EM: Fix potential division-by-zero error in em_compute_costs()

[Lukasz Luba <lukasz.luba@arm.com>]

On 4/17/25 02:07, Yaxiong Tian wrote:
> From: Yaxiong Tian <tianyaxiong@kylinos.cn>
> 
> 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>
> ---
>   kernel/power/energy_model.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index d9b7e2b38c7a..41606247c277 100644
> --- 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;


Please stop for a while. I have to check what happened that you
faced the issue in the first place. I have been testing the GPU
EMs and there was no issues...

Let me debug that today.