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Message-ID: <7882184.EvYhyI6sBW@rafael.j.wysocki>
Date: Fri, 26 Sep 2025 12:29:50 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: Shawn Guo <shawnguo@...nel.org>, Qais Yousef <qyousef@...alina.io>,
LKML <linux-kernel@...r.kernel.org>, Viresh Kumar <viresh.kumar@...aro.org>,
Pierre Gondois <pierre.gondois@....com>,
Mario Limonciello <mario.limonciello@....com>,
Linux ACPI <linux-acpi@...r.kernel.org>, Jie Zhan <zhanjie9@...ilicon.com>
Subject:
[PATCH v3 3/4] ACPI: CPPC: Do not use CPUFREQ_ETERNAL as an error value
From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Instead of using CPUFREQ_ETERNAL for signaling an error condition
in cppc_get_transition_latency(), change the return value type of
that function to int and make it return a proper negative error
code on failures.
No intentional functional impact.
Reviewed-by: Mario Limonciello (AMD) <superm1@...nel.org>
Reviewed-by: Jie Zhan <zhanjie9@...ilicon.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
v2 -> v3:
* Combine two if () statements in cppc_get_transition_latency() (Jie Zhan)
* Add tags from Mario Limonciello and Jie Zhan
v1 -> v2:
* Change cppc_get_transition_latency() return value data type to int
* Make it return -ENODATA on errors (Mario)
* Update its callers accordingly
* Adjust the subject and changelog
* Add a missing empty code line to cppc_get_transition_latency()
---
drivers/acpi/cppc_acpi.c | 16 +++++++---------
drivers/cpufreq/amd-pstate.c | 8 ++++----
drivers/cpufreq/cppc_cpufreq.c | 4 ++--
include/acpi/cppc_acpi.h | 6 +++---
4 files changed, 16 insertions(+), 18 deletions(-)
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1876,7 +1876,7 @@ EXPORT_SYMBOL_GPL(cppc_set_perf);
* If desired_reg is in the SystemMemory or SystemIo ACPI address space,
* then assume there is no latency.
*/
-unsigned int cppc_get_transition_latency(int cpu_num)
+int cppc_get_transition_latency(int cpu_num)
{
/*
* Expected transition latency is based on the PCCT timing values
@@ -1889,31 +1889,29 @@ unsigned int cppc_get_transition_latency
* completion of a command before issuing the next command,
* in microseconds.
*/
- unsigned int latency_ns = 0;
struct cpc_desc *cpc_desc;
struct cpc_register_resource *desired_reg;
int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu_num);
struct cppc_pcc_data *pcc_ss_data;
+ int latency_ns = 0;
cpc_desc = per_cpu(cpc_desc_ptr, cpu_num);
if (!cpc_desc)
- return CPUFREQ_ETERNAL;
+ return -ENODATA;
desired_reg = &cpc_desc->cpc_regs[DESIRED_PERF];
if (CPC_IN_SYSTEM_MEMORY(desired_reg) || CPC_IN_SYSTEM_IO(desired_reg))
return 0;
- else if (!CPC_IN_PCC(desired_reg))
- return CPUFREQ_ETERNAL;
- if (pcc_ss_id < 0)
- return CPUFREQ_ETERNAL;
+ if (!CPC_IN_PCC(desired_reg) || pcc_ss_id < 0)
+ return -ENODATA;
pcc_ss_data = pcc_data[pcc_ss_id];
if (pcc_ss_data->pcc_mpar)
latency_ns = 60 * (1000 * 1000 * 1000 / pcc_ss_data->pcc_mpar);
- latency_ns = max(latency_ns, pcc_ss_data->pcc_nominal * 1000);
- latency_ns = max(latency_ns, pcc_ss_data->pcc_mrtt * 1000);
+ latency_ns = max_t(int, latency_ns, pcc_ss_data->pcc_nominal * 1000);
+ latency_ns = max_t(int, latency_ns, pcc_ss_data->pcc_mrtt * 1000);
return latency_ns;
}
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -872,10 +872,10 @@ static void amd_pstate_update_limits(str
*/
static u32 amd_pstate_get_transition_delay_us(unsigned int cpu)
{
- u32 transition_delay_ns;
+ int transition_delay_ns;
transition_delay_ns = cppc_get_transition_latency(cpu);
- if (transition_delay_ns == CPUFREQ_ETERNAL) {
+ if (transition_delay_ns < 0) {
if (cpu_feature_enabled(X86_FEATURE_AMD_FAST_CPPC))
return AMD_PSTATE_FAST_CPPC_TRANSITION_DELAY;
else
@@ -891,10 +891,10 @@ static u32 amd_pstate_get_transition_del
*/
static u32 amd_pstate_get_transition_latency(unsigned int cpu)
{
- u32 transition_latency;
+ int transition_latency;
transition_latency = cppc_get_transition_latency(cpu);
- if (transition_latency == CPUFREQ_ETERNAL)
+ if (transition_latency < 0)
return AMD_PSTATE_TRANSITION_LATENCY;
return transition_latency;
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -310,9 +310,9 @@ static int cppc_verify_policy(struct cpu
static unsigned int __cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
{
- unsigned int transition_latency_ns = cppc_get_transition_latency(cpu);
+ int transition_latency_ns = cppc_get_transition_latency(cpu);
- if (transition_latency_ns == CPUFREQ_ETERNAL)
+ if (transition_latency_ns < 0)
return CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS / NSEC_PER_USEC;
return transition_latency_ns / NSEC_PER_USEC;
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -160,7 +160,7 @@ extern unsigned int cppc_khz_to_perf(str
extern bool acpi_cpc_valid(void);
extern bool cppc_allow_fast_switch(void);
extern int acpi_get_psd_map(unsigned int cpu, struct cppc_cpudata *cpu_data);
-extern unsigned int cppc_get_transition_latency(int cpu);
+extern int cppc_get_transition_latency(int cpu);
extern bool cpc_ffh_supported(void);
extern bool cpc_supported_by_cpu(void);
extern int cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val);
@@ -216,9 +216,9 @@ static inline bool cppc_allow_fast_switc
{
return false;
}
-static inline unsigned int cppc_get_transition_latency(int cpu)
+static inline int cppc_get_transition_latency(int cpu)
{
- return CPUFREQ_ETERNAL;
+ return -ENODATA;
}
static inline bool cpc_ffh_supported(void)
{
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