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cpufreq: Make policy min/max hard requirements

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When applying the policy min/max limits, the requested frequency is
simply clamped to not be out of range. It means, however, if one of the
boundaries isn't an available frequency, the frequency resolution can
return a value out of those limits, depending on the relation used.

e.g. freq{0,1,2} being available frequencies.

          freq0  policy->min  freq1  policy->max   freq2
            |        |          |        |           |
          17kHz     18kHz     19kHz     20kHz      21kHz

     __resolve_freq(21kHz, CPUFREQ_RELATION_L) -> 21kHz (out of bounds)
     __resolve_freq(17kHz, CPUFREQ_RELATION_H) -> 17kHz (out of bounds)

If, during the policy init, we resolve the requested min/max to existing
frequencies, we ensure that any CPUFREQ_RELATION_* would resolve to a
frequency which is inside the policy min/max range.

Making the policy limits rigid helps to introduce the inefficient
frequencies support. Resolving an inefficient frequency to an efficient
one should not transgress policy->max (which can be set for thermal
reason) and having a value we can trust simplify this comparison.

Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Vincent Donnefort 2021-09-08 15:05:26 +01:00 committed by Rafael J. Wysocki
parent 8354eb9eb3
commit 1517176906
1 changed files with 7 additions and 0 deletions
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7
drivers/cpufreq/cpufreq.c
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@ -2523,8 +2523,15 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
if (ret)
return ret;
/*
* Resolve policy min/max to available frequencies. It ensures
* no frequency resolution will neither overshoot the requested maximum
* nor undershoot the requested minimum.
*/
policy->min = new_data.min;
policy->max = new_data.max;
policy->min = __resolve_freq(policy, policy->min, CPUFREQ_RELATION_L);
policy->max = __resolve_freq(policy, policy->max, CPUFREQ_RELATION_H);
trace_cpu_frequency_limits(policy);
policy->cached_target_freq = UINT_MAX;