Re: [PATCH v2 1/2] cpufreq: tegra194: get consistent cpuinfo_cur_freq

[Sumit Gupta]

> > Frequency returned by 'cpuinfo_cur_freq' using counters is not fixed
> > and keeps changing slightly. This change returns a consistent value
> > from freq_table. If the reconstructed frequency has acceptable delta
> > from the last written value, then return the frequency corresponding
> > to the last written ndiv value from freq_table. Otherwise, print a
> > warning and return the reconstructed freq.
> >
> > Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
> > ---
> >   drivers/cpufreq/tegra194-cpufreq.c | 71 +++++++++++++++++++++++++++++++++-----
> >   1 file changed, 62 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/cpufreq/tegra194-cpufreq.c b/drivers/cpufreq/tegra194-cpufreq.c
> > index e1d931c..d250e49 100644
> > --- a/drivers/cpufreq/tegra194-cpufreq.c
> > +++ b/drivers/cpufreq/tegra194-cpufreq.c
> > @@ -180,9 +180,70 @@ static unsigned int tegra194_get_speed_common(u32 cpu, u32 delay)
> >        return (rate_mhz * KHZ); /* in KHz */
> >   }
> >
> > +static void get_cpu_ndiv(void *ndiv)
> > +{
> > +     u64 ndiv_val;
> > +
> > +     asm volatile("mrs %0, s3_0_c15_c0_4" : "=r" (ndiv_val) : );
> > +
> > +     *(u64 *)ndiv = ndiv_val;
> > +}
> > +
> > +static void set_cpu_ndiv(void *data)
>
> You weren't required to do this unnecessary change.
ya, moved the function up to keep both {get_|set_} calls together.

> > +{
> > +     struct cpufreq_frequency_table *tbl = data;
> > +     u64 ndiv_val = (u64)tbl->driver_data;
> > +
> > +     asm volatile("msr s3_0_c15_c0_4, %0" : : "r" (ndiv_val));
> > +}
> > +
> >   static unsigned int tegra194_get_speed(u32 cpu)
> >   {
> > -     return tegra194_get_speed_common(cpu, US_DELAY);
> > +     struct tegra194_cpufreq_data *data = cpufreq_get_driver_data();
> > +     struct cpufreq_frequency_table *pos;
> > +     unsigned int rate;
> > +     u64 ndiv;
> > +     int ret;
> > +     u32 cl;
> > +
> > +     if (!cpu_online(cpu))
>
> This isn't required. The CPU is guaranteed to be online here.
OK, will remove this in next version.

> > +             return -EINVAL;
> > +
> > +     smp_call_function_single(cpu, get_cpu_cluster, &cl, true);
> > +
> > +     if (cl >= data->num_clusters)
>
> Is it really possible here ? I meant you must have already checked
> this at cpufreq-init level already. Else mark it unlikely at least.
Ya, will remove the check here.

> > +             return -EINVAL;
> > +
> > +     /* reconstruct actual cpu freq using counters */
> > +     rate = tegra194_get_speed_common(cpu, US_DELAY);
> > +
> > +     /* get last written ndiv value */
> > +     ret = smp_call_function_single(cpu, get_cpu_ndiv, &ndiv, true);
> > +     if (ret) {
>
> What exactly can fail here ? get_cpu_ndiv() can't fail. Do we really
> need this check ? What about WARN_ON_ONCE() ?
OK.

> > +             pr_err("cpufreq: Failed to get ndiv for CPU%d, ret:%d\n",
> > +                    cpu, ret);
> > +             return rate;
> > +     }
> > +
> > +     /*
> > +      * If the reconstructed frequency has acceptable delta from
> > +      * the last written value, then return freq corresponding
> > +      * to the last written ndiv value from freq_table. This is
> > +      * done to return consistent value.
> > +      */
> > +     cpufreq_for_each_valid_entry(pos, data->tables[cl]) {
> > +             if (pos->driver_data != ndiv)
> > +                     continue;
> > +
> > +             if (abs(pos->frequency - rate) > 115200) {
>
> where does this 115200 comes from ? Strange that it matches tty's baud
> rate :)
> The value is equal to one freq step size.

> This is 115 MHz, right ? Isn't that too big of a delta ?
The is the acceptable delta used during our testing keeping some margin.

> > +                     pr_warn("cpufreq: cpu%d,cur:%u,set:%u,set ndiv:%llu\n",
> > +                             cpu, rate, pos->frequency, ndiv);
> > +             } else {
> > +                     rate = pos->frequency;
> > +             }
> > +             break;
> > +     }
> > +     return rate;
> >   }
>
> --
> viresh