linux-kernel - Re: [PATCH V3 10/15] cpufreq: mediatek: Add counter to prevent infinite loop when tracking voltage

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Date:   Fri, 15 Apr 2022 14:14:34 +0800
From:   Hsin-Yi Wang <hsinyi@...gle.com>
To:     Rex-BC Chen <rex-bc.chen@...iatek.com>
Cc:     rafael@...nel.org, Viresh Kumar <viresh.kumar@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, krzk+dt@...nel.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        Tim Chang <jia-wei.chang@...iatek.com>, roger.lu@...iatek.com,
        Kevin Hilman <khilman@...libre.com>,
        angelogioacchino.delregno@...labora.com, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH V3 10/15] cpufreq: mediatek: Add counter to prevent
 infinite loop when tracking voltage

On Fri, Apr 15, 2022 at 1:59 PM Rex-BC Chen <rex-bc.chen@...iatek.com> wrote:
>
> To prevent infinite loop when tracking voltage, we calculate the maximum
> value for each platform data.
> We assume min voltage is 0 and tracking target voltage using
> min_volt_shift for each iteration.
> The retry_max is 3 times of expeted iteration count.
>
> Signed-off-by: Rex-BC Chen <rex-bc.chen@...iatek.com>
> ---
>  drivers/cpufreq/mediatek-cpufreq.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/drivers/cpufreq/mediatek-cpufreq.c b/drivers/cpufreq/mediatek-cpufreq.c
> index cc44a7a9427a..d4c00237e862 100644
> --- a/drivers/cpufreq/mediatek-cpufreq.c
> +++ b/drivers/cpufreq/mediatek-cpufreq.c
> @@ -86,6 +86,16 @@ static int mtk_cpufreq_voltage_tracking(struct mtk_cpu_dvfs_info *info,
>         struct regulator *proc_reg = info->proc_reg;
>         struct regulator *sram_reg = info->sram_reg;
>         int pre_vproc, pre_vsram, new_vsram, vsram, vproc, ret;
> +       int retry_max;
> +
> +       /*
> +        * We assume min voltage is 0 and tracking target voltage using
> +        * min_volt_shift for each iteration.
> +        * The retry_max is 3 times of expeted iteration count.
> +        */
> +       retry_max = 3 * DIV_ROUND_UP(max(info->soc_data->sram_max_volt,
> +                                        info->soc_data->proc_max_volt),
> +                                    info->soc_data->min_volt_shift);

mtk_cpufreq_voltage_tracking() will be called very frequently.
retry_max is the same every time mtk_cpufreq_voltage_tracking() is
called. Is it better to calculate before and store in
mtk_cpu_dvfs_info?

>
>         pre_vproc = regulator_get_voltage(proc_reg);
>         if (pre_vproc < 0) {
> @@ -151,6 +161,12 @@ static int mtk_cpufreq_voltage_tracking(struct mtk_cpu_dvfs_info *info,
>
>                 pre_vproc = vproc;
>                 pre_vsram = vsram;
> +
> +               if (--retry_max < 0) {
> +                       dev_err(info->cpu_dev,
> +                               "over loop count, failed to set voltage\n");
> +                       return -EINVAL;
> +               }
>         } while (vproc != new_vproc || vsram != new_vsram);
>
>         return 0;
> --
> 2.18.0
>