[PATCH 1/1] cpufreq: Set policy->min and max as real QoS constraints

Pierre Gondois
2026-04-23T08:48:23Z

cpufreq_set_policy() will ultimately override the policy min/max
values written in the .init() callback through:
cpufreq_policy_online()
\-cpufreq_init_policy()
\-cpufreq_set_policy()
\-/* Set policy->min/max */
Thus the policy min/max values provided are only temporary.

There is an exception if CPUFREQ_NEED_INITIAL_FREQ_CHECK is set and:
cpufreq_policy_online()
\-cpufreq_init_policy()
\-__cpufreq_driver_target()
\-cpufreq_driver->target()
is called. To avoid any regression, set policy->min/max in cpufreq.c
if the values were not initialized.

In this patch:
- Setting policy->min or max value in driver .init() cb is
interpreted as setting a QoS constraint.
- Remove policy->min/max initialization in drivers if the values
are similar to policy->cpuinfo.min_freq/max_freq.
The only drivers where these values are different are:
- gx-suspmod.c
- cppc-cpufreq.c
- longrun.c
- For the cppc-cpufreq driver, the lowest non-linear freq. is
used as a min QoS constraint as suggested at:
https://lore.kernel.org/lkml/20260213100633.15413-1-zhangpengjie2@huawei.com/

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
---
drivers/cpufreq/amd-pstate.c | 16 ++++++++--------
drivers/cpufreq/cppc_cpufreq.c | 11 +++++++----
drivers/cpufreq/cpufreq-nforce2.c | 4 ++--
drivers/cpufreq/cpufreq.c | 19 +++++++++++++++++--
drivers/cpufreq/freq_table.c | 7 +++----
drivers/cpufreq/gx-suspmod.c | 9 +++++----
drivers/cpufreq/intel_pstate.c | 3 ---
drivers/cpufreq/pcc-cpufreq.c | 8 ++++----
drivers/cpufreq/pxa3xx-cpufreq.c | 4 ++--
drivers/cpufreq/sh-cpufreq.c | 4 ++--
drivers/cpufreq/virtual-cpufreq.c | 5 +----
11 files changed, 51 insertions(+), 39 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 453084c67327f..1ed4bcdcc957f 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1090,10 +1090,10 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)

perf = READ_ONCE(cpudata->perf);

- policy->cpuinfo.min_freq = policy->min = perf_to_freq(perf,
- cpudata->nominal_freq,
- perf.lowest_perf);
- policy->cpuinfo.max_freq = policy->max = cpudata->max_freq;
+ policy->cpuinfo.min_freq = perf_to_freq(perf,
+ cpudata->nominal_freq,
+ perf.lowest_perf);
+ policy->cpuinfo.max_freq = cpudata->max_freq;

policy->driver_data = cpudata;
ret = amd_pstate_cppc_enable(policy);
@@ -1907,10 +1907,10 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)

perf = READ_ONCE(cpudata->perf);

- policy->cpuinfo.min_freq = policy->min = perf_to_freq(perf,
- cpudata->nominal_freq,
- perf.lowest_perf);
- policy->cpuinfo.max_freq = policy->max = cpudata->max_freq;
+ policy->cpuinfo.min_freq = perf_to_freq(perf,
+ cpudata->nominal_freq,
+ perf.lowest_perf);
+ policy->cpuinfo.max_freq = cpudata->max_freq;
policy->driver_data = cpudata;

ret = amd_pstate_cppc_enable(policy);
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 7e7f9dfb7a24c..c6fcecdbbab0c 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -645,6 +645,7 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
unsigned int cpu = policy->cpu;
struct cppc_cpudata *cpu_data;
struct cppc_perf_caps *caps;
+ unsigned int min, max;
int ret;

cpu_data = cppc_cpufreq_get_cpu_data(cpu);
@@ -655,13 +656,15 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
caps = &cpu_data->perf_caps;
policy->driver_data = cpu_data;

+ min = cppc_perf_to_khz(caps, caps->lowest_nonlinear_perf);
+ max = cppc_perf_to_khz(caps, policy->boost_enabled ?
+ caps->highest_perf : caps->nominal_perf);
+
/*
* Set min to lowest nonlinear perf to avoid any efficiency penalty (see
* Section 8.4.7.1.1.5 of ACPI 6.1 spec)
*/
- policy->min = cppc_perf_to_khz(caps, caps->lowest_nonlinear_perf);
- policy->max = cppc_perf_to_khz(caps, policy->boost_enabled ?
- caps->highest_perf : caps->nominal_perf);
+ policy->min = min;

/*
* Set cpuinfo.min_freq to Lowest to make the full range of performance
@@ -669,7 +672,7 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
* nonlinear perf
*/
policy->cpuinfo.min_freq = cppc_perf_to_khz(caps, caps->lowest_perf);
- policy->cpuinfo.max_freq = policy->max;
+ policy->cpuinfo.max_freq = max;

policy->transition_delay_us = cppc_cpufreq_get_transition_delay_us(cpu);
policy->shared_type = cpu_data->shared_type;
diff --git a/drivers/cpufreq/cpufreq-nforce2.c b/drivers/cpufreq/cpufreq-nforce2.c
index fbbbe501cf2dc..831102522ad64 100644
--- a/drivers/cpufreq/cpufreq-nforce2.c
+++ b/drivers/cpufreq/cpufreq-nforce2.c
@@ -355,8 +355,8 @@ static int nforce2_cpu_init(struct cpufreq_policy *policy)
min_fsb = NFORCE2_MIN_FSB;

/* cpuinfo and default policy values */
- policy->min = policy->cpuinfo.min_freq = min_fsb * fid * 100;
- policy->max = policy->cpuinfo.max_freq = max_fsb * fid * 100;
+ policy->cpuinfo.min_freq = min_fsb * fid * 100;
+ policy->cpuinfo.max_freq = max_fsb * fid * 100;

return 0;
}
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 44eb1b7e7fc1b..b30bfa3e27daa 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1453,6 +1453,14 @@ static int cpufreq_policy_online(struct cpufreq_policy *policy,
cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);

if (new_policy) {
+ unsigned int min, max;
+
+ /* Use policy->min/max set by the driver as QoS requests. */
+ min = max(FREQ_QOS_MIN_DEFAULT_VALUE, policy->min);
+ if (policy->max)
+ max = min(FREQ_QOS_MAX_DEFAULT_VALUE, policy->max);
+ else
+ max = FREQ_QOS_MAX_DEFAULT_VALUE;
for_each_cpu(j, policy->related_cpus) {
per_cpu(cpufreq_cpu_data, j) = policy;
add_cpu_dev_symlink(policy, j, get_cpu_device(j));
@@ -1469,18 +1477,25 @@ static int cpufreq_policy_online(struct cpufreq_policy *policy,

ret = freq_qos_add_request(&policy->constraints,
&policy->min_freq_req, FREQ_QOS_MIN,
- FREQ_QOS_MIN_DEFAULT_VALUE);
+ min);
if (ret < 0)
goto out_destroy_policy;

ret = freq_qos_add_request(&policy->constraints,
&policy->max_freq_req, FREQ_QOS_MAX,
- FREQ_QOS_MAX_DEFAULT_VALUE);
+ max);
if (ret < 0)
goto out_destroy_policy;

blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
CPUFREQ_CREATE_POLICY, policy);
+
+ /*
+ * If the driver didn't set QoS constraints, policy->min/max still
+ * need to be set as they are used to clamp frequency requests.
+ */
+ policy->min = policy->min ? policy->min : policy->cpuinfo.min_freq;
+ policy->max = policy->max ? policy->max : policy->cpuinfo.max_freq;
}

if (cpufreq_driver->get && has_target()) {
diff --git a/drivers/cpufreq/freq_table.c b/drivers/cpufreq/freq_table.c
index 5b364d8da4f92..ea994647abc88 100644
--- a/drivers/cpufreq/freq_table.c
+++ b/drivers/cpufreq/freq_table.c
@@ -49,16 +49,15 @@ int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy)
max_freq = freq;
}

- policy->min = policy->cpuinfo.min_freq = min_freq;
- policy->max = max_freq;
+ policy->cpuinfo.min_freq = min_freq;
/*
* If the driver has set its own cpuinfo.max_freq above max_freq, leave
* it as is.
*/
if (policy->cpuinfo.max_freq < max_freq)
- policy->max = policy->cpuinfo.max_freq = max_freq;
+ policy->cpuinfo.max_freq = max_freq;

- if (policy->min == ~0)
+ if (min_freq == ~0)
return -EINVAL;
else
return 0;
diff --git a/drivers/cpufreq/gx-suspmod.c b/drivers/cpufreq/gx-suspmod.c
index d269a4f26f98e..ebda2bbebf44b 100644
--- a/drivers/cpufreq/gx-suspmod.c
+++ b/drivers/cpufreq/gx-suspmod.c
@@ -397,7 +397,7 @@ static int cpufreq_gx_target(struct cpufreq_policy *policy,

static int cpufreq_gx_cpu_init(struct cpufreq_policy *policy)
{
- unsigned int maxfreq;
+ unsigned int minfreq, maxfreq;

if (!policy || policy->cpu != 0)
return -ENODEV;
@@ -418,10 +418,11 @@ static int cpufreq_gx_cpu_init(struct cpufreq_policy *policy)
policy->cpu = 0;

if (max_duration < POLICY_MIN_DIV)
- policy->min = maxfreq / max_duration;
+ minfreq = maxfreq / max_duration;
else
- policy->min = maxfreq / POLICY_MIN_DIV;
- policy->max = maxfreq;
+ minfreq = maxfreq / POLICY_MIN_DIV;
+
+ policy->min = minfreq;
policy->cpuinfo.min_freq = maxfreq / max_duration;
policy->cpuinfo.max_freq = maxfreq;

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 1292da53e5fcb..68ccc6eb1ef30 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -3049,9 +3049,6 @@ static int __intel_pstate_cpu_init(struct cpufreq_policy *policy)
policy->cpuinfo.max_freq = READ_ONCE(global.no_turbo) ?
cpu->pstate.max_freq : cpu->pstate.turbo_freq;

- policy->min = policy->cpuinfo.min_freq;
- policy->max = policy->cpuinfo.max_freq;
-
intel_pstate_init_acpi_perf_limits(policy);

policy->fast_switch_possible = true;
diff --git a/drivers/cpufreq/pcc-cpufreq.c b/drivers/cpufreq/pcc-cpufreq.c
index ac2e90a65f0c4..231edfe8cabaa 100644
--- a/drivers/cpufreq/pcc-cpufreq.c
+++ b/drivers/cpufreq/pcc-cpufreq.c
@@ -551,13 +551,13 @@ static int pcc_cpufreq_cpu_init(struct cpufreq_policy *policy)
goto out;
}

- policy->max = policy->cpuinfo.max_freq =
+ policy->cpuinfo.max_freq =
ioread32(&pcch_hdr->nominal) * 1000;
- policy->min = policy->cpuinfo.min_freq =
+ policy->cpuinfo.min_freq =
ioread32(&pcch_hdr->minimum_frequency) * 1000;

- pr_debug("init: policy->max is %d, policy->min is %d\n",
- policy->max, policy->min);
+ pr_debug("init: max_freq is %d, min_freq is %d\n",
+ policy->cpuinfo.max_freq, policy->cpuinfo.min_freq);
out:
return result;
}
diff --git a/drivers/cpufreq/pxa3xx-cpufreq.c b/drivers/cpufreq/pxa3xx-cpufreq.c
index 50ff3b6a69000..181962b0924e6 100644
--- a/drivers/cpufreq/pxa3xx-cpufreq.c
+++ b/drivers/cpufreq/pxa3xx-cpufreq.c
@@ -185,8 +185,8 @@ static int pxa3xx_cpufreq_init(struct cpufreq_policy *policy)
int ret = -EINVAL;

/* set default policy and cpuinfo */
- policy->min = policy->cpuinfo.min_freq = 104000;
- policy->max = policy->cpuinfo.max_freq =
+ policy->cpuinfo.min_freq = 104000;
+ policy->cpuinfo.max_freq =
(cpu_is_pxa320()) ? 806000 : 624000;
policy->cpuinfo.transition_latency = 1000; /* FIXME: 1 ms, assumed */

diff --git a/drivers/cpufreq/sh-cpufreq.c b/drivers/cpufreq/sh-cpufreq.c
index 642ddb9ea217e..244153a1cead2 100644
--- a/drivers/cpufreq/sh-cpufreq.c
+++ b/drivers/cpufreq/sh-cpufreq.c
@@ -124,9 +124,9 @@ static int sh_cpufreq_cpu_init(struct cpufreq_policy *policy)
dev_notice(dev, "no frequency table found, falling back "
"to rate rounding.\n");

- policy->min = policy->cpuinfo.min_freq =
+ policy->cpuinfo.min_freq =
(clk_round_rate(cpuclk, 1) + 500) / 1000;
- policy->max = policy->cpuinfo.max_freq =
+ policy->cpuinfo.max_freq =
(clk_round_rate(cpuclk, ~0UL) + 500) / 1000;
}

diff --git a/drivers/cpufreq/virtual-cpufreq.c b/drivers/cpufreq/virtual-cpufreq.c
index 4159f31349b16..dc78b74409af4 100644
--- a/drivers/cpufreq/virtual-cpufreq.c
+++ b/drivers/cpufreq/virtual-cpufreq.c
@@ -164,10 +164,7 @@ static int virt_cpufreq_get_freq_info(struct cpufreq_policy *policy)
policy->cpuinfo.min_freq = 1;
policy->cpuinfo.max_freq = virt_cpufreq_get_perftbl_entry(policy->cpu, 0);

- policy->min = policy->cpuinfo.min_freq;
- policy->max = policy->cpuinfo.max_freq;
-
- policy->cur = policy->max;
+ policy->cur = policy->cpuinfo.max_freq;
return 0;
}

--
2.43.0