linux-kernel - Re: [PATCH] cpufreq: kyro: Reduce frame-size of qcom_cpufreq_kryo

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Date:   Thu, 21 Feb 2019 10:02:00 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>, Ilia Lin <ilia.lin@...nel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: kyro: Reduce frame-size of qcom_cpufreq_kryo_probe()

On Thu, Feb 21, 2019 at 9:15 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 20-02-19, 21:56, Amit Kucheria wrote:
> > On Wed, Feb 20, 2019 at 4:44 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > >
> > > With the introduction of commit 846a415bf440 ("arm64: default NR_CPUS to
> > > 256"), we have started getting following compilation warning:
> > >
> > > qcom-cpufreq-kryo.c:168:1: warning: the frame size of 2160 bytes is larger than 2048 bytes [-Wframe-larger-than=]
> > >
> > > Fix that by dynamically allocating opp_tables and freeing it later.
> > >
> > > Compile tested only.
> > >
> > > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > > ---
> > >  drivers/cpufreq/qcom-cpufreq-kryo.c | 9 ++++++++-
> > >  1 file changed, 8 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/cpufreq/qcom-cpufreq-kryo.c b/drivers/cpufreq/qcom-cpufreq-kryo.c
> > > index 1c8583cc06a2..6888cb6db2ef 100644
> > > --- a/drivers/cpufreq/qcom-cpufreq-kryo.c
> > > +++ b/drivers/cpufreq/qcom-cpufreq-kryo.c
> > > @@ -75,7 +75,7 @@ static enum _msm8996_version qcom_cpufreq_kryo_get_msm_id(void)
> > >
> > >  static int qcom_cpufreq_kryo_probe(struct platform_device *pdev)
> > >  {
> > > -       struct opp_table *opp_tables[NR_CPUS] = {0};
> > > +       struct opp_table **opp_tables;
> > >         enum _msm8996_version msm8996_version;
> > >         struct nvmem_cell *speedbin_nvmem;
> > >         struct device_node *np;
> > > @@ -133,6 +133,10 @@ static int qcom_cpufreq_kryo_probe(struct platform_device *pdev)
> > >         }
> > >         kfree(speedbin);
> > >
> > > +       opp_tables = kcalloc(num_possible_cpus(), sizeof(*opp_tables), GFP_KERNEL);
> > > +       if (!opp_tables)
> > > +               return -ENOMEM;
> > > +
> >
> > Perhaps add a comment above that that actual opp_table is allocated in
> > the loop below because of dev_pm_opp_set_supported_hw?
> >
> > I was staring at this for a few minutes wondering why you needed this
> > kcalloc before I realised that opp_tables (missed the 's') is a
> > temporary array of pointers. :-)
>
> I feel that you got confused because this patch didn't had the diff
> where the opp_tables thing is getting used. When we see the .c file
> itself, it is pretty much clear on what is going on and I believe the
> comment would be totally unnecessary and redundant.
>
> This is how it looks now, please lemme know if you still prefer the
> comment :)

Perhaps I was just unfamiliar with the dev_pm_opp_set_supported_hw()
API where the actual allocation happens 3 levels deep. Maybe the
comment should apply to dev_pm_opp_set_supported_hw(). I leave it to
you to decide.

>         opp_tables = kcalloc(num_possible_cpus(), sizeof(*opp_tables), GFP_KERNEL);
>         if (!opp_tables)
>                 return -ENOMEM;
>
>         for_each_possible_cpu(cpu) {
>                 cpu_dev = get_cpu_device(cpu);
>                 if (NULL == cpu_dev) {
>                         ret = -ENODEV;
>                         goto free_opp;
>                 }
>
>                 opp_tables[cpu] = dev_pm_opp_set_supported_hw(cpu_dev,
>                                                               &versions, 1);
>                 if (IS_ERR(opp_tables[cpu])) {
>                         ret = PTR_ERR(opp_tables[cpu]);
>                         dev_err(cpu_dev, "Failed to set supported hardware\n");
>                         goto free_opp;
>                 }
>         }
>
>         kfree(opp_tables);
>
>
> --
> viresh