[PATCH 5.15 240/917] cpufreq: Make policy min/max hard requirements

Greg Kroah-Hartman
2021-11-16T00:59:00Z

From: Vincent Donnefort <vincent.donnefort@arm.com>

[ Upstream commit 15171769069408789a72f9aa9a52cc931b839b56 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/cpufreq/cpufreq.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 5782b15a8caad..284e940084c61 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -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;
--
2.33.0