From: Shawn Guo shawnguo@kernel.org
A regression is seen with 6.6 -> 6.12 kernel upgrade on platforms where cpufreq-dt driver sets cpuinfo.transition_latency as CPUFREQ_ETERNAL (-1), due to that platform's DT doesn't provide the optional property 'clock-latency-ns'. The dbs sampling_rate was 10000 us on 6.6 and suddently becomes 6442450 us (4294967295 / 1000 * 1.5) on 6.12 for these platforms, because the default transition delay was dropped by the commits below.
commit 37c6dccd6837 ("cpufreq: Remove LATENCY_MULTIPLIER") commit a755d0e2d41b ("cpufreq: Honour transition_latency over transition_delay_us") commit e13aa799c2a6 ("cpufreq: Change default transition delay to 2ms")
It slows down dbs governor's reacting to CPU loading change dramatically. Also, as transition_delay_us is used by schedutil governor as rate_limit_us, it shows a negative impact on device idle power consumption, because the device gets slightly less time in the lowest OPP.
Fix the regressions by defining a default transition latency for handling the case of CPUFREQ_ETERNAL.
Cc: stable@vger.kernel.org Fixes: 37c6dccd6837 ("cpufreq: Remove LATENCY_MULTIPLIER") Signed-off-by: Shawn Guo shawnguo@kernel.org --- Changes for v2: - Follow Rafael's suggestion to define a default transition latency for handling CPUFREQ_ETERNAL, and pave the way to get rid of CPUFREQ_ETERNAL completely later.
v1: https://lkml.org/lkml/2025/9/10/294
drivers/cpufreq/cpufreq.c | 3 +++ include/linux/cpufreq.h | 2 ++ 2 files changed, 5 insertions(+)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index fc7eace8b65b..c69d10f0e8ec 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -549,6 +549,9 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy) if (policy->transition_delay_us) return policy->transition_delay_us;
+ if (policy->cpuinfo.transition_latency == CPUFREQ_ETERNAL) + policy->cpuinfo.transition_latency = CPUFREQ_DEFAULT_TANSITION_LATENCY_NS; + latency = policy->cpuinfo.transition_latency / NSEC_PER_USEC; if (latency) /* Give a 50% breathing room between updates */ diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 95f3807c8c55..935e9a660039 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -36,6 +36,8 @@ /* Print length for names. Extra 1 space for accommodating '\n' in prints */ #define CPUFREQ_NAME_PLEN (CPUFREQ_NAME_LEN + 1)
+#define CPUFREQ_DEFAULT_TANSITION_LATENCY_NS NSEC_PER_MSEC + struct cpufreq_governor;
enum cpufreq_table_sorting {
On 9/22/2025 8:59 PM, Shawn Guo wrote:
From: Shawn Guo shawnguo@kernel.org
A regression is seen with 6.6 -> 6.12 kernel upgrade on platforms where cpufreq-dt driver sets cpuinfo.transition_latency as CPUFREQ_ETERNAL (-1), due to that platform's DT doesn't provide the optional property 'clock-latency-ns'. The dbs sampling_rate was 10000 us on 6.6 and suddently becomes 6442450 us (4294967295 / 1000 * 1.5) on 6.12 for these platforms, because the default transition delay was dropped by the commits below.
commit 37c6dccd6837 ("cpufreq: Remove LATENCY_MULTIPLIER") commit a755d0e2d41b ("cpufreq: Honour transition_latency over transition_delay_us")
Hello Shawn,
Reported by checkpatch.pl: WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit description?) #12: commit a755d0e2d41b ("cpufreq: Honour transition_latency over transition_delay_us")
commit e13aa799c2a6 ("cpufreq: Change default transition delay to 2ms")
It slows down dbs governor's reacting to CPU loading change dramatically. Also, as transition_delay_us is used by schedutil governor as rate_limit_us, it shows a negative impact on device idle power consumption, because the device gets slightly less time in the lowest OPP.
Fix the regressions by defining a default transition latency for handling the case of CPUFREQ_ETERNAL.
Cc: stable@vger.kernel.org Fixes: 37c6dccd6837 ("cpufreq: Remove LATENCY_MULTIPLIER") Signed-off-by: Shawn Guo shawnguo@kernel.org
Changes for v2:
- Follow Rafael's suggestion to define a default transition latency for handling CPUFREQ_ETERNAL, and pave the way to get rid of CPUFREQ_ETERNAL completely later.
v1: https://lkml.org/lkml/2025/9/10/294
drivers/cpufreq/cpufreq.c | 3 +++ include/linux/cpufreq.h | 2 ++ 2 files changed, 5 insertions(+)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index fc7eace8b65b..c69d10f0e8ec 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -549,6 +549,9 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy) if (policy->transition_delay_us) return policy->transition_delay_us;
- if (policy->cpuinfo.transition_latency == CPUFREQ_ETERNAL)
policy->cpuinfo.transition_latency = CPUFREQ_DEFAULT_TANSITION_LATENCY_NS;
For the fallback case, May we print a dbg info in dmesg to inform developers that the device tree is missing the clock-latency-ns property? (Rafael can help comment~)
- latency = policy->cpuinfo.transition_latency / NSEC_PER_USEC; if (latency) /* Give a 50% breathing room between updates */
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 95f3807c8c55..935e9a660039 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -36,6 +36,8 @@ /* Print length for names. Extra 1 space for accommodating '\n' in prints */ #define CPUFREQ_NAME_PLEN (CPUFREQ_NAME_LEN + 1) +#define CPUFREQ_DEFAULT_TANSITION_LATENCY_NS NSEC_PER_MSEC
TANSITION --> TRANSITION ?
struct cpufreq_governor; enum cpufreq_table_sorting {
On Monday, September 22, 2025 2:59:21 PM CEST Shawn Guo wrote:
From: Shawn Guo shawnguo@kernel.org
A regression is seen with 6.6 -> 6.12 kernel upgrade on platforms where cpufreq-dt driver sets cpuinfo.transition_latency as CPUFREQ_ETERNAL (-1), due to that platform's DT doesn't provide the optional property 'clock-latency-ns'. The dbs sampling_rate was 10000 us on 6.6 and suddently becomes 6442450 us (4294967295 / 1000 * 1.5) on 6.12 for these platforms, because the default transition delay was dropped by the commits below.
commit 37c6dccd6837 ("cpufreq: Remove LATENCY_MULTIPLIER") commit a755d0e2d41b ("cpufreq: Honour transition_latency over transition_delay_us") commit e13aa799c2a6 ("cpufreq: Change default transition delay to 2ms")
It slows down dbs governor's reacting to CPU loading change dramatically. Also, as transition_delay_us is used by schedutil governor as rate_limit_us, it shows a negative impact on device idle power consumption, because the device gets slightly less time in the lowest OPP.
Fix the regressions by defining a default transition latency for handling the case of CPUFREQ_ETERNAL.
Cc: stable@vger.kernel.org Fixes: 37c6dccd6837 ("cpufreq: Remove LATENCY_MULTIPLIER") Signed-off-by: Shawn Guo shawnguo@kernel.org
Changes for v2:
- Follow Rafael's suggestion to define a default transition latency for handling CPUFREQ_ETERNAL, and pave the way to get rid of CPUFREQ_ETERNAL completely later.
v1: https://lkml.org/lkml/2025/9/10/294
drivers/cpufreq/cpufreq.c | 3 +++ include/linux/cpufreq.h | 2 ++ 2 files changed, 5 insertions(+)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index fc7eace8b65b..c69d10f0e8ec 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -549,6 +549,9 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy) if (policy->transition_delay_us) return policy->transition_delay_us;
- if (policy->cpuinfo.transition_latency == CPUFREQ_ETERNAL)
policy->cpuinfo.transition_latency = CPUFREQ_DEFAULT_TANSITION_LATENCY_NS;- latency = policy->cpuinfo.transition_latency / NSEC_PER_USEC; if (latency) /* Give a 50% breathing room between updates */
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 95f3807c8c55..935e9a660039 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -36,6 +36,8 @@ /* Print length for names. Extra 1 space for accommodating '\n' in prints */ #define CPUFREQ_NAME_PLEN (CPUFREQ_NAME_LEN + 1) +#define CPUFREQ_DEFAULT_TANSITION_LATENCY_NS NSEC_PER_MSEC
struct cpufreq_governor; enum cpufreq_table_sorting {
What about the appended (untested) change instead?
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)
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)
On Thu, Sep 25, 2025 at 10:15 AM Shawn Guo shawnguo2@yeah.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 notwork 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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