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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Jan 2026 10:52:47.0480 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 878641b9-17cf-4940-64b0-08de5cc90abe 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: DB1PEPF000509F9.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB8945 On 1/24/26 21:32, Sumit Gupta wrote: > > On 22/01/26 17:06, Pierre Gondois wrote: >> External email: Use caution opening links or attachments >> >> >> On 1/20/26 15:56, Sumit Gupta wrote: >>> Add cppc_get/set_min_perf() and cppc_get/set_max_perf() APIs to read >>> and >>> write the MIN_PERF and MAX_PERF registers. >>> >>> Also add sysfs interfaces (min_perf, max_perf) in cppc_cpufreq driver >>> to expose these controls to userspace. The sysfs values are in >>> frequency >>> (kHz) for consistency with other cpufreq sysfs files. >>> >>> A mutex is used to serialize sysfs store operations to ensure hardware >>> register writes and perf_ctrls updates are atomic. >>> >>> Signed-off-by: Sumit Gupta >>> --- >>>   drivers/acpi/cppc_acpi.c       |  44 +++++++++ >>>   drivers/cpufreq/cppc_cpufreq.c | 157 >>> +++++++++++++++++++++++++++++++++ >>>   include/acpi/cppc_acpi.h       |  20 +++++ >>>   3 files changed, 221 insertions(+) >>> >>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c >>> index 45c6bd6ec24b..46bf45f8b0f3 100644 >>> --- a/drivers/acpi/cppc_acpi.c >>> +++ b/drivers/acpi/cppc_acpi.c >>> @@ -1743,6 +1743,50 @@ int cppc_set_auto_sel(int cpu, bool enable) >>>   } >>>   EXPORT_SYMBOL_GPL(cppc_set_auto_sel); >>> >>> +/** >>> + * cppc_get_min_perf - Read minimum performance register. >>> + * @cpu: CPU from which to read register. >>> + * @min_perf: Return address. >>> + */ >>> +int cppc_get_min_perf(int cpu, u64 *min_perf) >>> +{ >>> +     return cppc_get_reg_val(cpu, MIN_PERF, min_perf); >>> +} >>> +EXPORT_SYMBOL_GPL(cppc_get_min_perf); >>> + >>> +/** >>> + * cppc_set_min_perf - Write minimum performance register. >>> + * @cpu: CPU to which to write register. >>> + * @min_perf: the desired minimum performance value to be updated. >>> + */ >>> +int cppc_set_min_perf(int cpu, u32 min_perf) >>> +{ >>> +     return cppc_set_reg_val(cpu, MIN_PERF, min_perf); >>> +} >>> +EXPORT_SYMBOL_GPL(cppc_set_min_perf); >>> + >>> +/** >>> + * cppc_get_max_perf - Read maximum performance register. >>> + * @cpu: CPU from which to read register. >>> + * @max_perf: Return address. >>> + */ >>> +int cppc_get_max_perf(int cpu, u64 *max_perf) >>> +{ >>> +     return cppc_get_reg_val(cpu, MAX_PERF, max_perf); >>> +} >>> +EXPORT_SYMBOL_GPL(cppc_get_max_perf); >>> + >>> +/** >>> + * cppc_set_max_perf - Write maximum performance register. >>> + * @cpu: CPU to which to write register. >>> + * @max_perf: the desired maximum performance value to be updated. >>> + */ >>> +int cppc_set_max_perf(int cpu, u32 max_perf) >>> +{ >>> +     return cppc_set_reg_val(cpu, MAX_PERF, max_perf); >>> +} >>> +EXPORT_SYMBOL_GPL(cppc_set_max_perf); >>> + >>>   /** >>>    * cppc_set_enable - Set to enable CPPC on the processor by >>> writing the >>>    * Continuous Performance Control package EnableRegister field. >>> diff --git a/drivers/cpufreq/cppc_cpufreq.c >>> b/drivers/cpufreq/cppc_cpufreq.c >>> index 229880c4eedb..66e183b45fb0 100644 >>> --- a/drivers/cpufreq/cppc_cpufreq.c >>> +++ b/drivers/cpufreq/cppc_cpufreq.c >>> @@ -28,6 +28,8 @@ >>> >>>   static struct cpufreq_driver cppc_cpufreq_driver; >>> >>> +static DEFINE_MUTEX(cppc_cpufreq_autonomous_lock); >>> + >> >> Shouldn't concurrent access be handled by the policy->rwsem ? >> >> I think this can be checked using either: >> - lockdep_assert_held_write(&policy->rwsem) >> - lockdep_assert_held_read(&policy->rwsem) >> >> in store/show_max_perf() for instance. >> > > You're right. The cpufreq sysfs already holds policy->rwsem for > show/store callbacks. I'll remove the mutex and add lockdep > assertions for the expected locking. I think it's ok not to have lockde assertions. It seems that it is a common assumption sysfs files cannot be modified concurrently. None of the cpufreq driver seems to use lockdep assertion. > -------- > File: drivers/cpufreq/cpufreq.c >   static ssize_t store(struct kobject *kobj, struct attribute *attr, >                      const char *buf, size_t count) >   { >       struct cpufreq_policy *policy = to_policy(kobj); >       .... >       guard(cpufreq_policy_write)(policy); > -------- > > Thank you, > Sumit Gupta >