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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: YgmYjRrLP2fxpox6DcaOpH+IElmdEpbA2r8I9700jC5rLn/Cs5BlL0oqHHgxu2ucujWz6vLBIJwGmgjp4QfLwTIcqbjeAXT4s765NjQzBI5GXnV9+JgrJl0du5GjZxipwOiIIEt89RP/jC+4lGzD6EHq9mUz8tDS6GAEJgUeHE/uFykMvindRfBa/Kn360J5UxEuDll0WLG0LlEqeexUnKhdgUc7aj5w0HucnJTnCJ3R4zz5Fg+ZFz9vJwKJ4sIQCx/YxZiZmJvCrTiuP7lu8kIRMZnR65Whnja4UMie55Jn28zzncj18AsyDccEAYmsE7NuQkyX8tqE49mfsFUTc2EITOkoAZb3Q/kRph6cM9HfU+xyB9f5cF6iPsXpi9gOViQ2bDByhLjm1b4W+LMMo8bvNMRzrY9NNsDrykwdTICqOWhfHPL3zPBQDozasi+n X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 May 2026 12:13:54.0009 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 6b5ff80f-fa5d-4e7c-6eb6-08debcb29611 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AMS0EPF00000191.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DU0PR08MB9824 Hello Sumit, On 5/27/26 21:46, Sumit Gupta wrote: > Expose the OSPM Nominal Performance register (ACPI 6.6, Section > 8.4.6.1.2.6), which conveys the desired nominal performance level > at which the platform may run. Unlike the existing read-only > Nominal Performance register, it is writable and lets OSPM > request a lower nominal level than the platform-reported nominal. > The platform classifies performance above this level as boosted > and below as throttled for its power/thermal decisions. > > It is exposed as a per-policy cpufreq sysfs attribute in kHz, to > match the cpufreq sysfs unit convention: > > /sys/devices/system/cpu/cpufreq/policyN/ospm_nominal_freq > > The attribute is documented in > Documentation/ABI/testing/sysfs-devices-system-cpu. > > Writes are converted to perf via cppc_khz_to_perf(), validated > against [Lowest Performance, Nominal Performance], and applied to > every CPU in policy->cpus. > > The register is write-only; the kernel caches the last written > value in struct cppc_cpudata for sysfs readback (returns 0 until > userspace writes a value). > > Signed-off-by: Sumit Gupta > --- > .../ABI/testing/sysfs-devices-system-cpu | 17 ++++++ > drivers/acpi/cppc_acpi.c | 35 +++++++++++ > drivers/cpufreq/cppc_cpufreq.c | 60 +++++++++++++++++++ > include/acpi/cppc_acpi.h | 12 ++++ > 4 files changed, 124 insertions(+) > > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu > index 82d10d556cc8..ac1bf1b89ac4 100644 > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu > @@ -346,6 +346,23 @@ 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: May 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 for power and thermal decisions. > + > + Read returns the last written value in kHz, or 0 if no > + value has been written. Write a kHz value in the range > + [lowest_freq, nominal_freq]. > + > + 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/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c > index c76cfafa3589..ad6ece16c30d 100644 > --- a/drivers/acpi/cppc_acpi.c > +++ b/drivers/acpi/cppc_acpi.c > @@ -1682,6 +1682,41 @@ int cppc_set_epp(int cpu, u64 epp_val) > } > EXPORT_SYMBOL_GPL(cppc_set_epp); > > +/** > + * cppc_set_ospm_nominal_perf() - Write OSPM Nominal Performance register. > + * @cpu: CPU on which to write register. > + * @ospm_nominal_perf: Value to write to the OSPM Nominal Performance register. > + * > + * OSPM Nominal Performance conveys the desired nominal performance level > + * at which the platform may run. Per ACPI 6.6, s8.4.6.1.2.6, the value > + * must lie within [Lowest Performance, Nominal Performance] and may be > + * set independently of Minimum, Maximum and Desired performance. > + * > + * Return: 0 on success or negative error code. > + */ > +int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf) > +{ > + struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu); > + struct cppc_perf_caps caps; > + int ret; > + > + if (!cpc_desc) { > + pr_debug("No CPC descriptor for CPU:%d\n", cpu); > + return -ENODEV; > + } > + > + ret = cppc_get_perf_caps(cpu, &caps); > + if (ret) > + return ret; > + > + if (ospm_nominal_perf < caps.lowest_perf || > + ospm_nominal_perf > caps.nominal_perf) > + return -EINVAL; > + > + return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf); > +} > +EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf); > + > /** > * cppc_get_auto_act_window() - Read autonomous activity window register. > * @cpu: CPU from which to read register. > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c > index 15a728dea911..5c54af1655b5 100644 > --- a/drivers/cpufreq/cppc_cpufreq.c > +++ b/drivers/cpufreq/cppc_cpufreq.c > @@ -1139,11 +1139,70 @@ 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) > +{ > + struct cppc_cpudata *cpu_data = policy->driver_data; > + unsigned int freq_khz; > + > + if (!cpu_data->ospm_nominal_perf_set) > + return sysfs_emit(buf, "0\n"); The questions on v3 might be more relevant, but for instance here, the ospm_nominal_perf value is not 0, the hardware register might contain any value. So reading the register might be more meaningful than returning 0.