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Message-ID: <CAJZ5v0jd+Th7cdbf7arto+spSbdvd37gk0YZEL5mh=0HK2id=Q@mail.gmail.com>
Date: Thu, 25 Sep 2025 13:16:02 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Shawn Guo <shawnguo2@...h.net>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, 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 Thu, Sep 25, 2025 at 10:15 AM Shawn Guo <shawnguo2@...h.net> wrote:
>
> 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.
These are not cleanup changes, just a different way to address the given issue.
Instead of pretending that it still works as documented even though
that's not the case strictly speaking, let's just get rid of it and
let the code be simpler at the same time.
> >
> > 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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