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Message-ID: <aNT3k9OK82USu4n8@dragon>
Date: Thu, 25 Sep 2025 16:04:35 +0800
From: Shawn Guo <shawnguo2@...h.net>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Shawn Guo <shawnguo@...nel.org>, Qais Yousef <qyousef@...alina.io>,
Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] cpufreq: Handle CPUFREQ_ETERNAL with a default
transition latency
On Mon, Sep 22, 2025 at 08:31:56PM +0200, Rafael J. Wysocki wrote:
> What about the appended (untested) change instead?
I'm trying to address a regression with a fix to be ported for stable
kernel. Not really sure it's a good idea to mix up with cleanup
changes.
Shawn
>
> With a follow-up one to replace CPUFREQ_ETERNAL with something internal
> to CPPC.
>
> ---
> Documentation/admin-guide/pm/cpufreq.rst | 4 ----
> Documentation/cpu-freq/cpu-drivers.rst | 3 +--
> Documentation/translations/zh_CN/cpu-freq/cpu-drivers.rst | 3 +--
> Documentation/translations/zh_TW/cpu-freq/cpu-drivers.rst | 3 +--
> drivers/cpufreq/cppc_cpufreq.c | 14 ++++++++++++--
> drivers/cpufreq/cpufreq-dt.c | 2 +-
> drivers/cpufreq/imx6q-cpufreq.c | 2 +-
> drivers/cpufreq/mediatek-cpufreq-hw.c | 2 +-
> drivers/cpufreq/scmi-cpufreq.c | 2 +-
> drivers/cpufreq/scpi-cpufreq.c | 2 +-
> drivers/cpufreq/spear-cpufreq.c | 2 +-
> include/linux/cpufreq.h | 7 ++++---
> 12 files changed, 25 insertions(+), 21 deletions(-)
>
> --- a/Documentation/admin-guide/pm/cpufreq.rst
> +++ b/Documentation/admin-guide/pm/cpufreq.rst
> @@ -274,10 +274,6 @@ are the following:
> The time it takes to switch the CPUs belonging to this policy from one
> P-state to another, in nanoseconds.
>
> - If unknown or if known to be so high that the scaling driver does not
> - work with the `ondemand`_ governor, -1 (:c:macro:`CPUFREQ_ETERNAL`)
> - will be returned by reads from this attribute.
> -
> ``related_cpus``
> List of all (online and offline) CPUs belonging to this policy.
>
> --- a/Documentation/cpu-freq/cpu-drivers.rst
> +++ b/Documentation/cpu-freq/cpu-drivers.rst
> @@ -109,8 +109,7 @@ Then, the driver must fill in the follow
> +-----------------------------------+--------------------------------------+
> |policy->cpuinfo.transition_latency | the time it takes on this CPU to |
> | | switch between two frequencies in |
> -| | nanoseconds (if appropriate, else |
> -| | specify CPUFREQ_ETERNAL) |
> +| | nanoseconds |
> +-----------------------------------+--------------------------------------+
> |policy->cur | The current operating frequency of |
> | | this CPU (if appropriate) |
> --- a/Documentation/translations/zh_CN/cpu-freq/cpu-drivers.rst
> +++ b/Documentation/translations/zh_CN/cpu-freq/cpu-drivers.rst
> @@ -112,8 +112,7 @@ CPUfreq核心层注册一个cpufreq_driv
> | | |
> +-----------------------------------+--------------------------------------+
> |policy->cpuinfo.transition_latency | CPU在两个频率之间切换所需的时间，以 |
> -| | 纳秒为单位（如不适用，设定为 |
> -| | CPUFREQ_ETERNAL） |
> +| | 纳秒为单位 |
> | | |
> +-----------------------------------+--------------------------------------+
> |policy->cur | 该CPU当前的工作频率(如适用) |
> --- a/Documentation/translations/zh_TW/cpu-freq/cpu-drivers.rst
> +++ b/Documentation/translations/zh_TW/cpu-freq/cpu-drivers.rst
> @@ -112,8 +112,7 @@ CPUfreq核心層註冊一個cpufreq_driv
> | | |
> +-----------------------------------+--------------------------------------+
> |policy->cpuinfo.transition_latency | CPU在兩個頻率之間切換所需的時間，以 |
> -| | 納秒爲單位（如不適用，設定爲 |
> -| | CPUFREQ_ETERNAL） |
> +| | 納秒爲單位 |
> | | |
> +-----------------------------------+--------------------------------------+
> |policy->cur | 該CPU當前的工作頻率(如適用) |
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -308,6 +308,16 @@ static int cppc_verify_policy(struct cpu
> return 0;
> }
>
> +static unsigned int get_transition_latency(unsigned int cpu)
> +{
> + unsigned int transition_latency_ns = cppc_get_transition_latency(cpu);
> +
> + if (transition_latency_ns == CPUFREQ_ETERNAL)
> + return CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS / NSEC_PER_USEC;
> +
> + return transition_latency_ns / NSEC_PER_USEC;
> +}
> +
> /*
> * The PCC subspace describes the rate at which platform can accept commands
> * on the shared PCC channel (including READs which do not count towards freq
> @@ -330,12 +340,12 @@ static unsigned int cppc_cpufreq_get_tra
> return 10000;
> }
> }
> - return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
> + return get_transition_latency(cpu);
> }
> #else
> static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
> {
> - return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
> + return get_transition_latency(cpu);
> }
> #endif
>
> --- a/drivers/cpufreq/cpufreq-dt.c
> +++ b/drivers/cpufreq/cpufreq-dt.c
> @@ -104,7 +104,7 @@ static int cpufreq_init(struct cpufreq_p
>
> transition_latency = dev_pm_opp_get_max_transition_latency(cpu_dev);
> if (!transition_latency)
> - transition_latency = CPUFREQ_ETERNAL;
> + transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> cpumask_copy(policy->cpus, priv->cpus);
> policy->driver_data = priv;
> --- a/drivers/cpufreq/imx6q-cpufreq.c
> +++ b/drivers/cpufreq/imx6q-cpufreq.c
> @@ -442,7 +442,7 @@ soc_opp_out:
> }
>
> if (of_property_read_u32(np, "clock-latency", &transition_latency))
> - transition_latency = CPUFREQ_ETERNAL;
> + transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> /*
> * Calculate the ramp time for max voltage change in the
> --- a/drivers/cpufreq/mediatek-cpufreq-hw.c
> +++ b/drivers/cpufreq/mediatek-cpufreq-hw.c
> @@ -309,7 +309,7 @@ static int mtk_cpufreq_hw_cpu_init(struc
>
> latency = readl_relaxed(data->reg_bases[REG_FREQ_LATENCY]) * 1000;
> if (!latency)
> - latency = CPUFREQ_ETERNAL;
> + latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> policy->cpuinfo.transition_latency = latency;
> policy->fast_switch_possible = true;
> --- a/drivers/cpufreq/scmi-cpufreq.c
> +++ b/drivers/cpufreq/scmi-cpufreq.c
> @@ -294,7 +294,7 @@ static int scmi_cpufreq_init(struct cpuf
>
> latency = perf_ops->transition_latency_get(ph, domain);
> if (!latency)
> - latency = CPUFREQ_ETERNAL;
> + latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> policy->cpuinfo.transition_latency = latency;
>
> --- a/drivers/cpufreq/scpi-cpufreq.c
> +++ b/drivers/cpufreq/scpi-cpufreq.c
> @@ -157,7 +157,7 @@ static int scpi_cpufreq_init(struct cpuf
>
> latency = scpi_ops->get_transition_latency(cpu_dev);
> if (!latency)
> - latency = CPUFREQ_ETERNAL;
> + latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> policy->cpuinfo.transition_latency = latency;
>
> --- a/drivers/cpufreq/spear-cpufreq.c
> +++ b/drivers/cpufreq/spear-cpufreq.c
> @@ -182,7 +182,7 @@ static int spear_cpufreq_probe(struct pl
>
> if (of_property_read_u32(np, "clock-latency",
> &spear_cpufreq.transition_latency))
> - spear_cpufreq.transition_latency = CPUFREQ_ETERNAL;
> + spear_cpufreq.transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> cnt = of_property_count_u32_elems(np, "cpufreq_tbl");
> if (cnt <= 0) {
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -26,12 +26,13 @@
> *********************************************************************/
> /*
> * Frequency values here are CPU kHz
> - *
> - * Maximum transition latency is in nanoseconds - if it's unknown,
> - * CPUFREQ_ETERNAL shall be used.
> */
>
> +/* Represents unknown transition latency */
> #define CPUFREQ_ETERNAL (-1)
> +
> +#define CPUFREQ_DEFAULT_TANSITION_LATENCY_NS NSEC_PER_MSEC
> +
> #define CPUFREQ_NAME_LEN 16
> /* Print length for names. Extra 1 space for accommodating '\n' in prints */
> #define CPUFREQ_NAME_PLEN (CPUFREQ_NAME_LEN + 1)
>
>
>
>
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