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SubjectRe: [PATCH v1 1/1] cpufreq: fix the target freq not in the range of policy->min & max
On Fri, Jun 25, 2021 at 3:41 PM TungChen Shih
<tung-chen.shih@mediatek.com> wrote:
>
> In cpufreq_frequency_table_target(), this function will try to find
> an index for @target_freq in freq_table, and the frequency of selected
> index should be in the range [policy->min, policy->max], which means:
>
> policy->min <= policy->freq_table[idx].frequency <= policy->max
>
> Though "clamp_val(target_freq, policy->min, policy->max);" would
> have been called to check this condition, when policy->max or min is
> not exactly one of the frequency in the frequency table,
> policy->freq_table[idx].frequency may still go out of the range
>
> For example, if our sorted freq_table is [3000, 2000, 1000], and
> suppose we have:
>
> @target_freq = 2500
> @policy->min = 2000
> @policy->max = 2200
> @relation = CPUFREQ_RELATION_L
>
> 1. After clamp_val(target_freq, policy->min, policy->max); @target_freq
> becomes 2200
> 2. Since we use CPUFREQ_REALTION_L, final selected freq will be 3000 which
> beyonds policy->max

As you accurately observed, the policy limits affect the target, not
the frequency that will be used, and "RELATION_L" means "the closest
frequency equal to or above the target".

You are not fixing a bug here IMO, you're changing the documented behavior.

> Signed-off-by: TungChen Shih <tung-chen.shih@mediatek.com>
> ---
> include/linux/cpufreq.h | 25 ++++++++++++++++++++++---
> 1 file changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index 353969c7acd3..60cb15740fdf 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -975,21 +975,40 @@ static inline int cpufreq_frequency_table_target(struct cpufreq_policy *policy,
> unsigned int target_freq,
> unsigned int relation)
> {
> + int idx = 0;
> if (unlikely(policy->freq_table_sorted == CPUFREQ_TABLE_UNSORTED))
> return cpufreq_table_index_unsorted(policy, target_freq,
> relation);
>
> switch (relation) {
> case CPUFREQ_RELATION_L:
> - return cpufreq_table_find_index_l(policy, target_freq);
> + idx = cpufreq_table_find_index_l(policy, target_freq);
> + break;
> case CPUFREQ_RELATION_H:
> - return cpufreq_table_find_index_h(policy, target_freq);
> + idx = cpufreq_table_find_index_h(policy, target_freq);
> + break;
> case CPUFREQ_RELATION_C:
> - return cpufreq_table_find_index_c(policy, target_freq);
> + idx = cpufreq_table_find_index_c(policy, target_freq);
> + break;
> default:
> WARN_ON_ONCE(1);
> return 0;
> }
> +
> + /* target index verification */
> + if (policy->freq_table[idx].frequency > policy->max) {
> + if (policy->freq_table_sorted == CPUFREQ_TABLE_SORTED_ASCENDING)
> + idx--;
> + else
> + idx++;
> + } else if (policy->freq_table[idx].frequency < policy->min) {
> + if (policy->freq_table_sorted == CPUFREQ_TABLE_SORTED_ASCENDING)
> + idx++;
> + else
> + idx--;
> + }
> +
> + return idx;
> }
>
> static inline int cpufreq_table_count_valid_entries(const struct cpufreq_policy *policy)
> --
> 2.18.0
>

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