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The platform treats performance above that level as boosted and below it as throttled. A lower value moves that boundary down, so more levels count as boost. Expose it as a per-policy cpufreq attribute in kHz, matching the unit convention of the other frequency attributes: /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq Writes are converted with cppc_khz_to_perf() and rejected unless they fall in [Lowest Performance, Nominal Performance]. The register cannot be read back, so a read returns the last value written, or "" before the first write. Also track the register in the OSPM-set save/restore table, so a requested value survives CPU hotplug and suspend/resume. The store handler records the request rather than init() capturing a firmware value, so the driver writes the register only once the OS has set it. CPU offline and driver unload write the platform-reported Nominal Performance to the register. Reviewed-by: Christian Loehle Signed-off-by: Sumit Gupta --- .../ABI/testing/sysfs-devices-system-cpu | 27 +++++ drivers/cpufreq/cppc_cpufreq.c | 101 ++++++++++++++++-- 2 files changed, 121 insertions(+), 7 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 545687ebadcc..6af7fa86e44c 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -350,6 +350,33 @@ Description: Performance Limited This file is only present if the cppc-cpufreq driver is in use. +What: /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq +Date: October 2026 +Contact: linux-pm@vger.kernel.org +Description: OSPM Nominal Performance (kHz) + + OSPM uses this attribute to request a nominal performance level + lower than the platform-reported nominal. The platform treats + performance above this level as boost and below as throttle. + + Write a value in kHz, between the frequencies corresponding to + Lowest Performance and Nominal Performance. + + The register cannot be read back, so a read returns the last + value written, rounded to a performance level. It returns + "" before the first write. Reads and writes fail with + -EOPNOTSUPP if the platform does not implement the register. + + Note that tasks may be migrated from one CPU to another by the + scheduler's load-balancing algorithm, and if different OSPM + Nominal Performance values are set for those CPUs (through + different cpufreq policies), that may lead to undesirable + outcomes. To avoid such issues it is better to set the same + value across all policies, or to pin every task potentially + sensitive to it to a specific CPU. + + This file is only present if the cppc-cpufreq driver is in use. + What: /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1} Date: August 2008 KernelVersion: 2.6.27 diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c index 76cb803617f5..662397526433 100644 --- a/drivers/cpufreq/cppc_cpufreq.c +++ b/drivers/cpufreq/cppc_cpufreq.c @@ -34,11 +34,13 @@ static struct cpufreq_driver cppc_cpufreq_driver; * reapplied from online() across CPU hotplug, and the firmware value is * restored from offline(). * - * Autonomous Selection (auto_sel) is kept first, as the registers after it - * only have meaning while it is enabled. + * Autonomous Selection (auto_sel) splits the list: the registers before it are + * independent of it, and those after it have meaning only while autonomous + * selection is enabled. Place a new register on the matching side. */ enum cppc_saved_reg_id { - CPPC_SAVED_AUTO_SEL, + CPPC_SAVED_OSPM_NOMINAL_PERF, + CPPC_SAVED_AUTO_SEL, /* Entries below need auto_sel enabled. */ CPPC_SAVED_EPP, CPPC_SAVED_AUTO_ACT_WINDOW, CPPC_NR_SAVED_REGS, @@ -51,6 +53,11 @@ struct cppc_saved_reg { }; static const struct cppc_saved_reg cppc_saved_regs[CPPC_NR_SAVED_REGS] = { + /* The register is write-only, so the driver tracks the requested value. */ + [CPPC_SAVED_OSPM_NOMINAL_PERF] = { + .name = "ospm_nominal_perf", + .set = cppc_set_ospm_nominal_perf, + }, [CPPC_SAVED_AUTO_SEL] = { .name = "auto_sel", .get = cppc_get_auto_sel, @@ -83,6 +90,9 @@ enum cppc_saved_type { * CPPC_SAVED_REQUESTED - value the OS asked for, reapplied at online(). * It starts as the firmware value and changes only * when a write from the OS succeeds. + * + * A write-only register cannot be read back. init() leaves both values unset, + * and its store handler sets them. */ struct cppc_policy_state { u64 regs[CPPC_NR_SAVED_REGS][CPPC_NR_SAVED_TYPES]; @@ -135,11 +145,19 @@ static int cppc_cpufreq_save_firmware_regs(struct cpufreq_policy *policy) int i, ret; for (i = 0; i < CPPC_NR_SAVED_REGS; i++) { - ret = cppc_saved_regs[i].get(cpu, &val); - if (ret == -EOPNOTSUPP) + const struct cppc_saved_reg *reg = &cppc_saved_regs[i]; + + if (!reg->get) { + /* A write-only register has no value to read. */ val = U64_MAX; - else if (ret) - return ret; + } else { + ret = reg->get(cpu, &val); + /* Leave a register the platform does not implement unset. */ + if (ret == -EOPNOTSUPP) + val = U64_MAX; + else if (ret) + return ret; + } st->regs[i][CPPC_SAVED_FIRMWARE] = val; st->regs[i][CPPC_SAVED_REQUESTED] = val; @@ -198,6 +216,12 @@ static void cppc_cpufreq_apply_saved_regs(struct cpufreq_policy *policy, u64 auto_sel, val; int i; + /* Registers before auto_sel do not depend on it. */ + for (i = 0; i < CPPC_SAVED_AUTO_SEL; i++) { + val = st->regs[i][saved_type]; + cppc_cpufreq_write_saved_reg(cpu, i, val, saved_type); + } + auto_sel = st->regs[CPPC_SAVED_AUTO_SEL][saved_type]; if (auto_sel) @@ -1470,11 +1494,73 @@ static int cppc_get_perf_limited_filtered(int cpu, u64 *perf_limited) CPPC_CPUFREQ_ATTR_RW_U64(perf_limited, cppc_get_perf_limited_filtered, cppc_set_perf_limited) +static ssize_t show_ospm_nominal_freq(struct cpufreq_policy *policy, char *buf) +{ + const struct cppc_policy_state *st = cppc_cpufreq_policy_state(policy); + struct cppc_cpudata *cpu_data = policy->driver_data; + u64 perf; + + if (!cppc_ospm_nominal_perf_supported(policy->cpu)) + return -EOPNOTSUPP; + + /* The register cannot be read back, so report the tracked request. */ + perf = st->regs[CPPC_SAVED_OSPM_NOMINAL_PERF][CPPC_SAVED_REQUESTED]; + if (perf == U64_MAX) + return sysfs_emit(buf, "\n"); + + return sysfs_emit(buf, "%u\n", + cppc_perf_to_khz(&cpu_data->perf_caps, perf)); +} + +static ssize_t store_ospm_nominal_freq(struct cpufreq_policy *policy, + const char *buf, size_t count) +{ + struct cppc_cpudata *cpu_data = policy->driver_data; + struct cppc_policy_state *st; + unsigned int freq_khz; + u32 perf; + int ret; + + ret = kstrtouint(buf, 0, &freq_khz); + if (ret) + return ret; + + perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz); + if (perf < cpu_data->perf_caps.lowest_perf || + perf > cpu_data->perf_caps.nominal_perf) + return -EINVAL; + + ret = cppc_set_ospm_nominal_perf(policy->cpu, perf); + if (ret) + return ret; + + /* + * The OS can write this register but cannot read it back. + * + * The register lets the OS ask for a nominal level below the platform + * Nominal Performance. offline() and driver unload write the platform + * Nominal in place of the requested value. This removes the lower + * level the OS asked for. The value from before the first OS write + * cannot be read, so the driver cannot restore it. online() writes + * the requested value again. + * + * Set both values here and not at init(). The driver then writes the + * register only after the OS has set it. + */ + st = cppc_cpufreq_policy_state(policy); + st->regs[CPPC_SAVED_OSPM_NOMINAL_PERF][CPPC_SAVED_REQUESTED] = perf; + st->regs[CPPC_SAVED_OSPM_NOMINAL_PERF][CPPC_SAVED_FIRMWARE] = + cpu_data->perf_caps.nominal_perf; + + return count; +} + cpufreq_freq_attr_ro(freqdomain_cpus); cpufreq_freq_attr_rw(auto_select); cpufreq_freq_attr_rw(auto_act_window); cpufreq_freq_attr_rw(energy_performance_preference_val); cpufreq_freq_attr_rw(perf_limited); +cpufreq_freq_attr_rw(ospm_nominal_freq); static struct freq_attr *cppc_cpufreq_attr[] = { &freqdomain_cpus, @@ -1482,6 +1568,7 @@ static struct freq_attr *cppc_cpufreq_attr[] = { &auto_act_window, &energy_performance_preference_val, &perf_limited, + &ospm_nominal_freq, NULL, }; -- 2.34.1