Re: [PATCH V6 02/15] cpufreq: Add cpufreq_table_len()

[Viresh Kumar]

On 07-01-25, 12:59, Greg KH wrote:
> On Tue, Jan 07, 2025 at 04:51:35PM +0530, Viresh Kumar wrote:
> > Add a function to calculate number of entries in the cpufreq table. This
> > will be used by the Rust implementation.
> 
> Again, why is Rust unique here?  Why wouldn't the C code also need this?

How about this:

    cpufreq: Add cpufreq_table_len()

    The last entry of a cpufreq table is marked by setting the frequency
    field to a special value: CPUFREQ_TABLE_END. The C code manages to
    traverse the table by checking the frequency field, until it reaches
    CPUFREQ_TABLE_END.

    The Rust cpufreq bindings though will need to know the length of the
    cpufreq table in advance, for example to check against an invalid index
    value.

    Provide a helper to calculate number of entries in the cpufreq table.
    will be used by the Rust implementation.

> > Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> > ---
> >  include/linux/cpufreq.h | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> > index 7fe0981a7e46..6b882ff4dc24 100644
> > --- a/include/linux/cpufreq.h
> > +++ b/include/linux/cpufreq.h
> > @@ -783,6 +783,17 @@ bool cpufreq_boost_enabled(void);
> >  int cpufreq_enable_boost_support(void);
> >  bool policy_has_boost_freq(struct cpufreq_policy *policy);
> >  
> > +static inline unsigned int cpufreq_table_len(struct cpufreq_frequency_table *freq_table)
> > +{
> > +	struct cpufreq_frequency_table *pos;
> > +	unsigned int count = 0;
> > +
> > +	cpufreq_for_each_entry(pos, freq_table)
> > +		count++;
> 
> No locking is needed?

No, the cpufreq table is implemented as an array and is never altered once
created.

-- 
viresh