Re: [PATCH v3 2/2] ACPI: CPPC: Add ospm_nominal_perf support

Hello Sumit,

I copy-pasted and attached a complementary patch just to show
what I meant by caching the ospm_nominal_perf value at driver
init/exit.

This should also allow to handle the cases where a user tries
to store a new value for a policy with multiple CPUs,
one of the CPUs and we need to rollback.

I think another issue that should be solved is that:

- we don't the value of ospm_nominal_perf when loading the driver

- we leave the register in an unknown state if we unload/reload
the driver.

Note:
IMO caching values like in the patch would also benefit to the
auto_sel register.

------

If you think the patch helps, feel free to take it. Otherwise
please let me know the issues it would raise.

Regards,

Pierre


On 5/14/26 21:48, 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 <[email protected]>
> ---
>   .../ABI/testing/sysfs-devices-system-cpu      | 17 ++++++++
>   drivers/acpi/cppc_acpi.c                      | 35 ++++++++++++++++
>   drivers/cpufreq/cppc_cpufreq.c                | 40 +++++++++++++++++++
>   include/acpi/cppc_acpi.h                      |  7 ++++
>   4 files changed, 99 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:	[email protected]
> +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 7e7f9dfb7a24..6379b7ceee34 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -985,11 +985,50 @@ store_energy_performance_preference_val(struct cpufreq_policy *policy,
>   CPPC_CPUFREQ_ATTR_RW_U64(perf_limited, cppc_get_perf_limited,
>   			 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)
> +		return sysfs_emit(buf, "0\n");
> +
> +	freq_khz = cppc_perf_to_khz(&cpu_data->perf_caps,
> +				    cpu_data->ospm_nominal_perf);
> +	return sysfs_emit(buf, "%u\n", freq_khz);
> +}
> +
> +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;
> +	unsigned int sib;
> +	u64 freq_khz;
> +	u32 perf;
> +	int ret;
> +
> +	ret = kstrtou64(buf, 0, &freq_khz);
> +	if (ret)
> +		return ret;
> +
> +	perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
> +
> +	for_each_cpu(sib, policy->cpus) {
> +		ret = cppc_set_ospm_nominal_perf(sib, perf);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	cpu_data->ospm_nominal_perf = 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,
> @@ -997,6 +1036,7 @@ static struct freq_attr *cppc_cpufreq_attr[] = {
>   	&auto_act_window,
>   	&energy_performance_preference_val,
>   	&perf_limited,
> +	&ospm_nominal_freq,
>   	NULL,
>   };
>   
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index 8693890a7275..0b1dcdbea10a 100644
> --- a/include/acpi/cppc_acpi.h
> +++ b/include/acpi/cppc_acpi.h
> @@ -153,6 +153,8 @@ struct cppc_cpudata {
>   	struct cppc_perf_fb_ctrs perf_fb_ctrs;
>   	unsigned int shared_type;
>   	cpumask_var_t shared_cpu_map;
> +	/* Cached OSPM Nominal Performance value (write-only register). */
> +	u32 ospm_nominal_perf;
>   };
>   
>   #ifdef CONFIG_ACPI_CPPC_LIB
> @@ -180,6 +182,7 @@ extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val);
>   extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf);
>   extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable);
>   extern int cppc_set_epp(int cpu, u64 epp_val);
> +extern int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf);
>   extern int cppc_get_auto_act_window(int cpu, u64 *auto_act_window);
>   extern int cppc_set_auto_act_window(int cpu, u64 auto_act_window);
>   extern int cppc_get_auto_sel(int cpu, bool *enable);
> @@ -266,6 +269,10 @@ static inline int cppc_set_epp(int cpu, u64 epp_val)
>   {
>   	return -EOPNOTSUPP;
>   }
> +static inline int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
> +{
> +	return -EOPNOTSUPP;
> +}
>   static inline int cppc_get_auto_act_window(int cpu, u64 *auto_act_window)
>   {
>   	return -EOPNOTSUPP;


diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu 
b/Documentation/ABI/testing/sysfs-devices-system-cpu
index ac1bf1b89ac4d..f3d357917242a 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -356,9 +356,7 @@Description:        OSPM Nominal Performance (kHz)
                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].
+Values are in kHz and in the range [lowest_freq, nominal_freq].

                This file is only present if the cppc-cpufreq driver is
                in use.
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 97218c4ac162b..01542184e69b2 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1717,6 +1717,19 @@int cppc_set_ospm_nominal_perf(int cpu, u64 
ospm_nominal_perf)
}
EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);

+/**
+ * cppc_get_ospm_nominal_perf() - Read OSPM Nominal Performance register.
+ * @cpu: CPU from which to read register.
+ * @ospm_nominal_perf: Pointer to store the OSPM Nominal Performance value.
+ *
+ * Return: 0 on success or negative error code.
+ */
+int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
+{
+return cppc_get_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
+}
+EXPORT_SYMBOL_GPL(cppc_get_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 6379b7ceee347..1a51017a81630 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -28,6 +28,9 @@

static struct cpufreq_driver cppc_cpufreq_driver;

+/* Values at driver init. */
+static u64 scratch_ospm_nominal_perf[NR_CPUS];
+
#ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
static enum {
        FIE_UNSET = -1,
@@ -642,7 +645,7 @@static void cppc_cpufreq_put_cpu_data(struct 
cpufreq_policy *policy)

static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
{
-       unsigned int cpu = policy->cpu;
+unsigned int sib, cpu = policy->cpu;
        struct cppc_cpudata *cpu_data;
        struct cppc_perf_caps *caps;
        int ret;
@@ -704,6 +707,34 @@static int cppc_cpufreq_cpu_init(struct 
cpufreq_policy *policy)
        if (caps->highest_perf > caps->nominal_perf)
                policy->boost_supported = true;

+/*
+ * CPUs are expected to have:
+ *   ospm_nominal_perf = nominal_perf
+ * at policy init.
+ */
+cpu_data->ospm_nominal_perf = caps->nominal_perf;
+
+for_each_cpu(sib, policy->cpus) {
+u64 ospm_nominal_perf;
+
+ret = cppc_get_ospm_nominal_perf(sib, &ospm_nominal_perf);
+if (ret == -EOPNOTSUPP) {
+continue;
+} else if (ret) {
+pr_err("CPU%d: Could not read ospm_nominal_perf value\n",
+sib);
+goto out;
+}
+
+if (ospm_nominal_perf != caps->nominal_perf) {
+pr_err("Incoherent ospm_nominal_perf values: "
+"scratch_value=%llu expected_value=%u\n",
+scratch_ospm_nominal_perf[sib],
+caps->nominal_perf);
+goto out;
+}
+}
+
        /* Set policy->cur to max now. The governors will adjust later. */
        policy->cur = cppc_perf_to_khz(caps, caps->highest_perf);
        cpu_data->perf_ctrls.desired_perf =  caps->highest_perf;
@@ -727,9 +758,17 @@static void cppc_cpufreq_cpu_exit(struct 
cpufreq_policy *policy)
{
        struct cppc_cpudata *cpu_data = policy->driver_data;
        struct cppc_perf_caps *caps = &cpu_data->perf_caps;
-       unsigned int cpu = policy->cpu;
+unsigned int sib, cpu = policy->cpu;
        int ret;

+/*
+ * CPUs are expected to have:
+ *   ospm_nominal_perf = nominal_perf
+ * at policy init, so come back to that state.
+ */
+for_each_cpu(sib, policy->cpus)
+cppc_set_ospm_nominal_perf(sib, caps->nominal_perf);
+
        cppc_cpufreq_cpu_fie_exit(policy);

        cpu_data->perf_ctrls.desired_perf = caps->lowest_perf;
@@ -989,9 +1028,20 @@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;
+u64 perf;
+int ret;
+
+ret = cppc_get_ospm_nominal_perf(policy->cpu, &perf);
+if (ret == -EOPNOTSUPP)
+return sysfs_emit(buf, "<unsupported>\n");
+if (ret)
+return ret;

-       if (!cpu_data->ospm_nominal_perf)
-               return sysfs_emit(buf, "0\n");
+if (perf != cpu_data->ospm_nominal_perf) {
+pr_warn("ospm_nominal_freq value is not coherent: "
+"register=%llu scratch_value=%u\n",
+perf, cpu_data->ospm_nominal_perf);
+}

        freq_khz = cppc_perf_to_khz(&cpu_data->perf_caps,
                                    cpu_data->ospm_nominal_perf);
@@ -1002,7 +1052,7 @@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;
-       unsigned int sib;
+unsigned int sib, failing_cpu;
        u64 freq_khz;
        u32 perf;
        int ret;
@@ -1015,12 +1065,23 @@static ssize_t store_ospm_nominal_freq(struct 
cpufreq_policy *policy,

        for_each_cpu(sib, policy->cpus) {
                ret = cppc_set_ospm_nominal_perf(sib, perf);
-               if (ret)
-                       return ret;
+if (ret) {
+failing_cpu = sib;
+goto error;
+}
        }

        cpu_data->ospm_nominal_perf = perf;
        return count;
+
+error:
+for_each_cpu(sib, policy->cpus) {
+if (sib == failing_cpu)
+break;
+cppc_set_ospm_nominal_perf(sib, cpu_data->ospm_nominal_perf);
+}
+
+return ret;
}

cpufreq_freq_attr_ro(freqdomain_cpus);
@@ -1053,6 +1114,64 @@static struct cpufreq_driver cppc_cpufreq_driver = {
        .name = "cppc_cpufreq",
};

+static void __exit cppc_cpufreq_ospm_nominal_perf_exit(void)
+{
+int cpu;
+
+for_each_present_cpu(cpu) {
+if (scratch_ospm_nominal_perf[cpu] == U64_MAX)
+continue;
+
+/* Reset ospm_nominal_perf to the value present at init. */
+cppc_set_ospm_nominal_perf(cpu, scratch_ospm_nominal_perf[cpu]);
+}
+}
+
+static int __init cppc_cpufreq_ospm_nominal_perf_init(void)
+{
+int ret, cpu;
+
+ret = 0;
+
+for_each_present_cpu(cpu) {
+u64 nominal_perf;
+
+/*
+ * If one CPU failed, scratch_ospm_nominal_perf still needs
+ * to be initialized.
+ */
+if (ret) {
+scratch_ospm_nominal_perf[cpu] = U64_MAX;
+continue;
+}
+
+ret = cppc_get_ospm_nominal_perf(cpu, &scratch_ospm_nominal_perf[cpu]);
+if (ret) {
+if (ret == -EOPNOTSUPP) {
+/* Valid reason to fail. Continue to iterate. */
+ret = 0;
+}
+
+scratch_ospm_nominal_perf[cpu] = U64_MAX;
+continue;
+}
+
+/* Set ospm_nominal_perf to nominal_perf before policy init. */
+ret = cppc_get_nominal_perf(cpu, &nominal_perf);
+if (ret)
+continue;
+
+ret = cppc_set_ospm_nominal_perf(cpu, nominal_perf);
+if (ret)
+continue;
+}
+
+if (ret)
+cppc_cpufreq_ospm_nominal_perf_exit();
+
+return ret;
+}
+
static int __init cppc_cpufreq_init(void)
{
        int ret;
@@ -1063,9 +1182,17 @@static int __init cppc_cpufreq_init(void)
        cppc_freq_invariance_init();
        populate_efficiency_class();

+ret = cppc_cpufreq_ospm_nominal_perf_init();
+if (ret) {
+cppc_freq_invariance_exit();
+return ret;
+}
+
        ret = cpufreq_register_driver(&cppc_cpufreq_driver);
-       if (ret)
+if (ret) {
+cppc_cpufreq_ospm_nominal_perf_exit();
                cppc_freq_invariance_exit();
+}

        return ret;
}
@@ -1074,6 +1201,7 @@static void __exit cppc_cpufreq_exit(void)
{
        cpufreq_unregister_driver(&cppc_cpufreq_driver);
        cppc_freq_invariance_exit();
+cppc_cpufreq_ospm_nominal_perf_exit();
}

module_exit(cppc_cpufreq_exit);
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index 0b1dcdbea10a2..07e6598fa837a 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -183,6 +183,7 @@extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf);
extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls 
*perf_ctrls, bool enable);
extern int cppc_set_epp(int cpu, u64 epp_val);
extern int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf);
+extern int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf);
extern int cppc_get_auto_act_window(int cpu, u64 *auto_act_window);
extern int cppc_set_auto_act_window(int cpu, u64 auto_act_window);
extern int cppc_get_auto_sel(int cpu, bool *enable);
@@ -273,6 +274,10 @@static inline int cppc_set_ospm_nominal_perf(int 
cpu, u64 ospm_nominal_perf)
{
        return -EOPNOTSUPP;
}
+static inline int cppc_get_ospm_nominal_perf(int cpu, u64 
*ospm_nominal_perf)
+{
+return -EOPNOTSUPP;
+}
static inline int cppc_get_auto_act_window(int cpu, u64 *auto_act_window)
{
        return -EOPNOTSUPP;

From 28a1fd8e94f860a3bbf135779fa399621e9355ad Mon Sep 17 00:00:00 2001
From: Pierre Gondois <[email protected]>
Date: Thu, 21 May 2026 14:53:46 +0200
Subject: [PATCH] ACPI: CPPC: Add ospm_nominal_perf support additional changes

Complementary modifications to:
- "ACPI: CPPC: Add ospm_nominal_perf support"

Signed-off-by: Pierre Gondois <[email protected]>
---
 .../ABI/testing/sysfs-devices-system-cpu      |   4 +-
 drivers/acpi/cppc_acpi.c                      |  13 ++
 drivers/cpufreq/cppc_cpufreq.c                | 144 +++++++++++++++++-
 include/acpi/cppc_acpi.h                      |   5 +
 4 files changed, 155 insertions(+), 11 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index ac1bf1b89ac4d..f3d357917242a 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -356,9 +356,7 @@ Description:	OSPM Nominal Performance (kHz)
 		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].
+		Values are in kHz and in the range [lowest_freq, nominal_freq].
 
 		This file is only present if the cppc-cpufreq driver is
 		in use.
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 97218c4ac162b..01542184e69b2 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1717,6 +1717,19 @@ int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
 }
 EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);
 
+/**
+ * cppc_get_ospm_nominal_perf() - Read OSPM Nominal Performance register.
+ * @cpu: CPU from which to read register.
+ * @ospm_nominal_perf: Pointer to store the OSPM Nominal Performance value.
+ *
+ * Return: 0 on success or negative error code.
+ */
+int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
+{
+	return cppc_get_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
+}
+EXPORT_SYMBOL_GPL(cppc_get_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 6379b7ceee347..1a51017a81630 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -28,6 +28,9 @@
 
 static struct cpufreq_driver cppc_cpufreq_driver;
 
+/* Values at driver init. */
+static u64 scratch_ospm_nominal_perf[NR_CPUS];
+
 #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
 static enum {
 	FIE_UNSET = -1,
@@ -642,7 +645,7 @@ static void cppc_cpufreq_put_cpu_data(struct cpufreq_policy *policy)
 
 static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 {
-	unsigned int cpu = policy->cpu;
+	unsigned int sib, cpu = policy->cpu;
 	struct cppc_cpudata *cpu_data;
 	struct cppc_perf_caps *caps;
 	int ret;
@@ -704,6 +707,34 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	if (caps->highest_perf > caps->nominal_perf)
 		policy->boost_supported = true;
 
+	/*
+	 * CPUs are expected to have:
+	 *   ospm_nominal_perf = nominal_perf
+	 * at policy init.
+	 */
+	cpu_data->ospm_nominal_perf = caps->nominal_perf;
+
+	for_each_cpu(sib, policy->cpus) {
+		u64 ospm_nominal_perf;
+
+		ret = cppc_get_ospm_nominal_perf(sib, &ospm_nominal_perf);
+		if (ret == -EOPNOTSUPP) {
+			continue;
+		} else if (ret) {
+			pr_err("CPU%d: Could not read ospm_nominal_perf value\n",
+				sib);
+			goto out;
+		}
+
+		if (ospm_nominal_perf != caps->nominal_perf) {
+			pr_err("Incoherent ospm_nominal_perf values: "
+				"scratch_value=%llu expected_value=%u\n",
+				scratch_ospm_nominal_perf[sib],
+				caps->nominal_perf);
+			goto out;
+		}
+	}
+
 	/* Set policy->cur to max now. The governors will adjust later. */
 	policy->cur = cppc_perf_to_khz(caps, caps->highest_perf);
 	cpu_data->perf_ctrls.desired_perf =  caps->highest_perf;
@@ -727,9 +758,17 @@ static void cppc_cpufreq_cpu_exit(struct cpufreq_policy *policy)
 {
 	struct cppc_cpudata *cpu_data = policy->driver_data;
 	struct cppc_perf_caps *caps = &cpu_data->perf_caps;
-	unsigned int cpu = policy->cpu;
+	unsigned int sib, cpu = policy->cpu;
 	int ret;
 
+	/*
+	 * CPUs are expected to have:
+	 *   ospm_nominal_perf = nominal_perf
+	 * at policy init, so come back to that state.
+	 */
+	for_each_cpu(sib, policy->cpus)
+		cppc_set_ospm_nominal_perf(sib, caps->nominal_perf);
+
 	cppc_cpufreq_cpu_fie_exit(policy);
 
 	cpu_data->perf_ctrls.desired_perf = caps->lowest_perf;
@@ -989,9 +1028,20 @@ 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;
+	u64 perf;
+	int ret;
+
+	ret = cppc_get_ospm_nominal_perf(policy->cpu, &perf);
+	if (ret == -EOPNOTSUPP)
+		return sysfs_emit(buf, "<unsupported>\n");
+	if (ret)
+		return ret;
 
-	if (!cpu_data->ospm_nominal_perf)
-		return sysfs_emit(buf, "0\n");
+	if (perf != cpu_data->ospm_nominal_perf) {
+		pr_warn("ospm_nominal_freq value is not coherent: "
+			"register=%llu scratch_value=%u\n",
+			perf, cpu_data->ospm_nominal_perf);
+	}
 
 	freq_khz = cppc_perf_to_khz(&cpu_data->perf_caps,
 				    cpu_data->ospm_nominal_perf);
@@ -1002,7 +1052,7 @@ 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;
-	unsigned int sib;
+	unsigned int sib, failing_cpu;
 	u64 freq_khz;
 	u32 perf;
 	int ret;
@@ -1015,12 +1065,23 @@ static ssize_t store_ospm_nominal_freq(struct cpufreq_policy *policy,
 
 	for_each_cpu(sib, policy->cpus) {
 		ret = cppc_set_ospm_nominal_perf(sib, perf);
-		if (ret)
-			return ret;
+		if (ret) {
+			failing_cpu = sib;
+			goto error;
+		}
 	}
 
 	cpu_data->ospm_nominal_perf = perf;
 	return count;
+
+error:
+	for_each_cpu(sib, policy->cpus) {
+		if (sib == failing_cpu)
+			break;
+		cppc_set_ospm_nominal_perf(sib, cpu_data->ospm_nominal_perf);
+	}
+
+	return ret;
 }
 
 cpufreq_freq_attr_ro(freqdomain_cpus);
@@ -1053,6 +1114,64 @@ static struct cpufreq_driver cppc_cpufreq_driver = {
 	.name = "cppc_cpufreq",
 };
 
+static void __exit cppc_cpufreq_ospm_nominal_perf_exit(void)
+{
+	int cpu;
+
+	for_each_present_cpu(cpu) {
+		if (scratch_ospm_nominal_perf[cpu] == U64_MAX)
+			continue;
+
+		/* Reset ospm_nominal_perf to the value present at init. */
+		cppc_set_ospm_nominal_perf(cpu, scratch_ospm_nominal_perf[cpu]);
+	}
+}
+
+static int __init cppc_cpufreq_ospm_nominal_perf_init(void)
+{
+	int ret, cpu;
+
+	ret = 0;
+
+	for_each_present_cpu(cpu) {
+		u64 nominal_perf;
+
+		/*
+		 * If one CPU failed, scratch_ospm_nominal_perf still needs
+		 * to be initialized.
+		 */
+		if (ret) {
+			scratch_ospm_nominal_perf[cpu] = U64_MAX;
+			continue;
+		}
+
+		ret = cppc_get_ospm_nominal_perf(cpu, &scratch_ospm_nominal_perf[cpu]);
+		if (ret) {
+			if (ret == -EOPNOTSUPP) {
+				/* Valid reason to fail. Continue to iterate. */
+				ret = 0;
+			}
+
+			scratch_ospm_nominal_perf[cpu] = U64_MAX;
+			continue;
+		}
+
+		/* Set ospm_nominal_perf to nominal_perf before policy init. */
+		ret = cppc_get_nominal_perf(cpu, &nominal_perf);
+		if (ret)
+			continue;
+
+		ret = cppc_set_ospm_nominal_perf(cpu, nominal_perf);
+		if (ret)
+			continue;
+	}
+
+	if (ret)
+		cppc_cpufreq_ospm_nominal_perf_exit();
+
+	return ret;
+}
+
 static int __init cppc_cpufreq_init(void)
 {
 	int ret;
@@ -1063,9 +1182,17 @@ static int __init cppc_cpufreq_init(void)
 	cppc_freq_invariance_init();
 	populate_efficiency_class();
 
+	ret = cppc_cpufreq_ospm_nominal_perf_init();
+	if (ret) {
+		cppc_freq_invariance_exit();
+		return ret;
+	}
+
 	ret = cpufreq_register_driver(&cppc_cpufreq_driver);
-	if (ret)
+	if (ret) {
+		cppc_cpufreq_ospm_nominal_perf_exit();
 		cppc_freq_invariance_exit();
+	}
 
 	return ret;
 }
@@ -1074,6 +1201,7 @@ static void __exit cppc_cpufreq_exit(void)
 {
 	cpufreq_unregister_driver(&cppc_cpufreq_driver);
 	cppc_freq_invariance_exit();
+	cppc_cpufreq_ospm_nominal_perf_exit();
 }
 
 module_exit(cppc_cpufreq_exit);
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index 0b1dcdbea10a2..07e6598fa837a 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -183,6 +183,7 @@ extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf);
 extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable);
 extern int cppc_set_epp(int cpu, u64 epp_val);
 extern int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf);
+extern int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf);
 extern int cppc_get_auto_act_window(int cpu, u64 *auto_act_window);
 extern int cppc_set_auto_act_window(int cpu, u64 auto_act_window);
 extern int cppc_get_auto_sel(int cpu, bool *enable);
@@ -273,6 +274,10 @@ static inline int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
 {
 	return -EOPNOTSUPP;
 }
+static inline int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
+{
+	return -EOPNOTSUPP;
+}
 static inline int cppc_get_auto_act_window(int cpu, u64 *auto_act_window)
 {
 	return -EOPNOTSUPP;
-- 
2.43.0