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Message-ID: <3b982e8d-4ce7-4186-b5f0-f7495be3a3ed@kernel.org>
Date: Thu, 25 Sep 2025 13:33:14 -0500
From: "Mario Limonciello (AMD) (kernel.org)" <superm1@...nel.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
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>,
Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] ACPI: CPPC: Do not use CPUFREQ_ETERNAL as an error
value
On 9/25/2025 12:23 PM, Rafael J. Wysocki wrote:
> 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.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@...nel.org>
> ---
>
> 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()
>
> The modifications of this patch don't affect any other patches in the series:
>
> https://lore.kernel.org/linux-pm/8605612.T7Z3S40VBb@rafael.j.wysocki/
>
> ---
> drivers/acpi/cppc_acpi.c | 15 ++++++++-------
> drivers/cpufreq/amd-pstate.c | 8 ++++----
> drivers/cpufreq/cppc_cpufreq.c | 4 ++--
> include/acpi/cppc_acpi.h | 6 +++---
> 4 files changed, 17 insertions(+), 16 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 +1889,32 @@ 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;
> + return -ENODATA;
>
> if (pcc_ss_id < 0)
> - return CPUFREQ_ETERNAL;
> + 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 get_transition_latency_from_cppc(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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