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

[Viresh Kumar]

On 09-01-25, 08:35, Greg KH wrote:
> Then why not make the C code use this function as well, to keep all
> cpufreq drivers from having to manually walk the list and that way both
> C and Rust drivers all do the same thing?  That makes more sense to me,
> there's no reason you can't change C code today first to make things
> more unified, in fact, that's usually a better idea overall anyway.

I investigated a bit on this..

- The cpufreq core normally gets (from cpufreq governor's for example)
  a frequency value to be matched against in the freq-table, and the
  loop which run over the freq-table is already optimized enough (it
  checks for CPUFREQ_TABLE_END) for this. Using length in this loop
  won't improve it anymore.

- The cpufreq core then calls cpufreq driver's callbacks and passes an
  index to the freq-table, which the drivers don't need to verify
  against table length, since the index came from the core itself.

- The same happens on the Rust side, where the cpufreq core calls the
  target_index() callback of the driver. While writing the Rust code,
  I thought maybe I should validate that the index is within limits
  (before I do pointer manipulation in Rust code). And so required
  this extra function (which C code never uses).

- Now I can either keep doing this verification in the Rust code (and
  so keep the new API, only used by Rust code). Or I can just remove
  the verification and trust that the index passed by the
  cpufreq-drivers is correct (since they have received them from the
  cpufreq C code).

What should I do ?

-- 
viresh