From: Pierre Gondois <Pierre.Gondois@arm.com> mainline inclusion from mainline-v5.18-rc1 commit ec1c7ad47664f964c1101fe555b6fde0cb124b38 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8WAED Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- CPUfreq governors request CPU frequencies using information on current CPU usage. The CPPC driver converts them to performance requests. Frequency targets are computed as: target_freq = (util / cpu_capacity) * max_freq target_freq is then clamped between [policy->min, policy->max]. The CPPC driver converts performance values to frequencies (and vice-versa) using cppc_cpufreq_perf_to_khz() and cppc_cpufreq_khz_to_perf(). These functions both use two different factors depending on the range of the input value. For cppc_cpufreq_khz_to_perf(): - (NOMINAL_PERF / NOMINAL_FREQ) or - (LOWEST_PERF / LOWEST_FREQ) and for cppc_cpufreq_perf_to_khz(): - (NOMINAL_FREQ / NOMINAL_PERF) or - ((NOMINAL_PERF - LOWEST_FREQ) / (NOMINAL_PERF - LOWEST_PERF)) This means: 1- the functions are not inverse for some values: (perf_to_khz(khz_to_perf(x)) != x) 2- cppc_cpufreq_perf_to_khz(LOWEST_PERF) can sometimes give a different value from LOWEST_FREQ due to integer approximation 3- it is implied that performance and frequency are proportional (NOMINAL_FREQ / NOMINAL_PERF) == (LOWEST_PERF / LOWEST_FREQ) This patch changes the conversion functions to an affine function. This fixes the 3 points above. Suggested-by: Lukasz Luba <lukasz.luba@arm.com> Suggested-by: Morten Rasmussen <morten.rasmussen@arm.com> Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Zeng Heng <zengheng4@huawei.com> --- drivers/cpufreq/cppc_cpufreq.c | 43 +++++++++++++++++----------------- 1 file changed, 21 insertions(+), 22 deletions(-) diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c index f7f3632dcf31..bb955318c024 100644 --- a/drivers/cpufreq/cppc_cpufreq.c +++ b/drivers/cpufreq/cppc_cpufreq.c @@ -89,35 +89,34 @@ static u64 cppc_get_dmi_max_khz(void) /* * If CPPC lowest_freq and nominal_freq registers are exposed then we can - * use them to convert perf to freq and vice versa - * - * If the perf/freq point lies between Nominal and Lowest, we can treat - * (Low perf, Low freq) and (Nom Perf, Nom freq) as 2D co-ordinates of a line - * and extrapolate the rest - * For perf/freq > Nominal, we use the ratio perf:freq at Nominal for conversion + * use them to convert perf to freq and vice versa. The conversion is + * extrapolated as an affine function passing by the 2 points: + * - (Low perf, Low freq) + * - (Nominal perf, Nominal perf) */ static unsigned int cppc_cpufreq_perf_to_khz(struct cppc_cpudata *cpu, unsigned int perf) { static u64 max_khz; struct cppc_perf_caps *caps = &cpu->perf_caps; + s64 retval, offset = 0; u64 mul, div; if (caps->lowest_freq && caps->nominal_freq) { - if (perf >= caps->nominal_perf) { - mul = caps->nominal_freq; - div = caps->nominal_perf; - } else { - mul = caps->nominal_freq - caps->lowest_freq; - div = caps->nominal_perf - caps->lowest_perf; - } + mul = caps->nominal_freq - caps->lowest_freq; + div = caps->nominal_perf - caps->lowest_perf; + offset = caps->nominal_freq - div64_u64(caps->nominal_perf * mul, div); } else { if (!max_khz) max_khz = cppc_get_dmi_max_khz(); mul = max_khz; div = caps->highest_perf; } - return (u64)perf * mul / div; + + retval = offset + div64_u64(perf * mul, div); + if (retval >= 0) + return retval; + return 0; } static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu, @@ -125,16 +124,13 @@ static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu, { static u64 max_khz; struct cppc_perf_caps *caps = &cpu->perf_caps; + s64 retval, offset = 0; u64 mul, div; if (caps->lowest_freq && caps->nominal_freq) { - if (freq >= caps->nominal_freq) { - mul = caps->nominal_perf; - div = caps->nominal_freq; - } else { - mul = caps->lowest_perf; - div = caps->lowest_freq; - } + mul = caps->nominal_perf - caps->lowest_perf; + div = caps->nominal_freq - caps->lowest_freq; + offset = caps->nominal_perf - div64_u64(caps->nominal_freq * mul, div); } else { if (!max_khz) max_khz = cppc_get_dmi_max_khz(); @@ -142,7 +138,10 @@ static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu, div = max_khz; } - return (u64)freq * mul / div; + retval = offset + div64_u64(freq * mul, div); + if (retval >= 0) + return retval; + return 0; } static int cppc_cpufreq_set_target(struct cpufreq_policy *policy, -- 2.25.1