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

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Date:   Mon, 18 Apr 2022 09:40:51 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        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>,
        <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 14:24 +0200, AngeloGioacchino Del Regno wrote:
> Il 15/04/22 08:14, Hsin-Yi Wang ha scritto:
> > 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>
> 
> I'm sorry Rex, but this commit has to be squashed with 09/15, as the
> logic is
> that each commit has to be acceptable, and 09/15 is not, without this
> fix.
> 
> Besides, as Hsin-Yi suggested, calculating this every time may hit
> performance,
> but at the same time I don't want to lose this explicit
> calculation...
> 

Hello Angelo,

I will squash thius patch into 9/15 and will use info->vtrack_max to
record the value in probe function.

Thanks!

BRs,
Rex

> > > ---
> > >   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?
> > 
> 
> ...so I agree with this solution: perhaps you can add a "vtrack_max"
> variable to
> mtk_cpu_dvfs_info as suggested, and fill in that one in function
> mtk_cpu_dvfs_info_init(), where we effectively initialize all-the-
> things.
> 
> Cheers,
> Angelo