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 14:29:03 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     Hsin-Yi Wang <hsinyi@...gle.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, 2022-04-15 at 14:14 +0800, Hsin-Yi Wang wrote:
> 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?
> 

Hello Hsin-Yi,

Thanks for your reviwew.
I will do this in next version.

BRs,
Rex

> > 
> >         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
> >